General Transmission

Mainline pressure should be checked in all gear ranges and at the three basic engine speeds.

1) If the pressures in all operating gears are within specifications at slow idle, the pump and pressure regulators are working fine. 2) If all pressures are low at slow idle but within spec at fast idle it is likely that there is a problem in the pump, pressure regulator, filter, or fluid level, or there is an internal pressure leak. 3) A gradual drop pressure change when the engine is operating at idle to wide-open throttle (WOT) in each gear range indicates a restricted fluid filter because the fluid cannot pass through the filter fast enough to meet the needs of the transmission and faster turning pump. 4) If the fluid pressure did not change with the increase in engine speed, a stuck pressure regulator may still allow the pressure to build with an increase in engine speed, but it will not provide the necessary boost pressures. 5) If the pressures are high at slow idle, the cause may be a faulty pressure regulator or throttle valve problem, or the transmission may be in fail safe mode. 6) If all of the pressures are low at WOT, pull on the throttle valve (TV) cable or disconnect the vacuum hose leading to the vacuum modulator to see if pressure returns to spec. 7) If they are high at slow idle and WOT, a faulty pressure regulator or throttle system is indicated. 8) If the pressures are normal at slow idle and high at WOT, the throttle system is faulty.

A common means of testing the control system and the ability of the transmission to generate pressure.

1) Take a pressure reading when the throttle is at minimum opening this should be the lowest pressure reading obtained. 2) Disconnecting the pressure control solenoid or using a bi-directional scanner to command the solenoid off should generate the highest pressure.

Inspect, adjust, and replace cables or linkages for the throttle valve (TV) and accelerator pedal.

A misadjusted TV linkage may also result in a throttle pressure that is too low in relation to the amount the throttle plates are open, causing early upshifts. Throttle pressure that is too high can cause harsh and delayed upshifts, and part throttle and WOT downshifts will occur earlier than normal. Very small changes in throttle cable adjustment can make a big difference in shift timing and feel.

Low fluid levels problems.

Aerated fluid can cause slow-pressure buildup and low-pressures. Air in the pressure regulator valve will cause a buzzing noise when the valve tries to regulate pump pressure.

Disassembly and Assembly Inspect valve body mating surfaces, bores, valves, solenoids, springs, sleeves, retainers, brackets, checkballs, screens, spacer plates, and gaskets; replace as necessary.

After all of the valves and springs have been removed from the valve body, soak the valve body and spacer plates in mineral spirits for a few minutes. Thoroughly clean all parts and make sure all passages within the valve body are clear and free of debris. Carefully blow-dry each part individually with dry compressed air. If the valve cannot be cleaned well enough to move freely in its bore, the valve body should be replaced. If the valve body has been severely contaminated with metal particles, it should be replaced, especially if it is aluminum. Replacement is necessary for several reasons: 1) Although some parts are available separately for valve bodies, spool valves usually are not. 2) Aluminum valve body bore-to-spool clearances are much tighter than older cast-iron bodies, making it easy to create an oversized or out-of-round bore using conventional techniques for bore repair. 3) Also, techniques used in the past to correct a scratched valve spool land do not work well with aluminum or "anodized" aluminum valve spools. Individual valves are lapped to a particular valve body, and, therefore, if any parts need to be replaced, the entire valve body must be replaced. With a straightedge and feeler gauge, check the flatness of the valve body's sealing surface.

Air test the operation of clutch and servo assemblies.

After the clearance of the clutch pack is set, perform an air test on each clutch. This test will verify that all of the seals and check balls in the hydraulic components are able to hold and release pressure. Air checks can also be made with the transmission assembled. This is the absolute best way to check the condition of the circuit because there are very few components missing from the circuit. The manufacturers of different transmissions have designed test plates that are available to test different hydraulic circuits. Testing with the transmission assembled also allows for testing of the servos. Many transmissions' clutch assemblies can be air tested by installing the fluid pump assembly with its reaction shaft support over the input shaft and sliding it in place on the front clutch drum. When the clutch drums are mounted on the fluid pump, all components in the circuit can be checked. If the clutch cannot be checked in this manner, blocking off apply ports with your finger and applying air pressure through the other clutch apply port will work. Invert the entire assembly and place it in an open vise or transmission support tool. Then air test the circuit using the test hole designated for that clutch. Be sure to use low-pressure compressed air (25 to 35 psi (85 to 119 kpa) to avoid damage to the seals. High-pressure air may blow the rubber seals out of the bore or roll them on the piston. While applying air pressure, you may notice some air escaping at the metal of the Teflon seal areas. This is normal, as these seals have a controlled amount of leakage designed into them. This is also true with some piston-applied clutch packs; what is most important is that a "thud" is heard, indicating the piston has moved, applying the clutch pack. Experience will dictate what is a normal amount of air bypassing (hissing) at these apply pressures with these clutch assemblies. It should release quickly without any delay or binding. If no evidence of piston movement is heard, examine the check ball seat for evidence of air leakage.

Perform torque converter clutch (lock-up converter) electronic system tests; determine necessary action.

All testing of TCC components should begin with a basic inspection of wires. The electronic control unit has a tight and clean connection. Also check the source voltage at the battery if not between 12 and 14.3 volts, the electronic system may not function properly. Hydraulically TCC-equipped vehicles, lock-up was controlled by a switch valve which is controlled by two other valves. The lock-up valve responds to governor pressure and prevents lock-up at speeds below 40 mph (64 km/h). The second, the fail safe valve responds to throttle pressure and permits lock-up in high gear only. Before the lock-up clutch is applied these key sensors the VSS, ECTS, TPS, and brake switch should be inspected as part of your diagnosis. The transmission range (TR) sensor is capable of causing more issues with several systems of the vehicle at one time than any other input. The TR sensor can be digital or analog. The digital type is easy to diagnose with a scan tool looking for each input as the shifter is moved. The analog type is looking for a specific voltage at each position throughout shifter travel. Many vehicles use pressure switches to confirm the hydraulic action needed to engage that gear occurred. Pressure switches either open or close an electrical circuit and are used to tell the PCM digitally that the transmission has indeed completed a shift and which gear. The throttle position sensor (TPS) is a potentiometer. A potentiometer is a three-wire sensor that consists of a voltage reference wire (typically 5 volts), a signal wire, and a signal return (ground) wire. The TPS signal of 0.5-1.0V DC when throttle is closed and increases the voltage to around 4-5V DC as the throttle is opened. The TPS signal can affect mainline pressure and shift schedule more than any other input. The vehicle speed sensor (VSS) creates a digital pulse or AC sine wave depending on type used. Two types of temperature sensors are mainly of two varieties. One designs infer temperature of the transmission from the engine's temperature sensor. Some ETC's have temperature sensors located in the reservoir or outlet cooler line of the transmission. Most sensor resistance will decrease as the temperature of the fluid increases. Since these are slow-moving signals, it is safe to perform preliminary testing by comparing actual temperature to the information provided by the scan tool. Turbine speed and output shaft speed sensors are used to monitor the shaft speeds within the transmission, compare them to engine rpm, and, in some cases, replace the vehicle speed sensor input. They allow for complex shift schedules that allow the engine to operate at the appropriate torque output for almost any driving condition. They are also used for comparative diagnostic operations within the PCM to determine torque converter and gear train slippage. Their signals are very similar to the VSS signal and can best be monitored with a labscope in a real time driving situation. The scan tool is also an excellent way to determine the PCM's perceived inputs from each. A DVOM and a schematic of the system are needed when trying to diagnose any wiring problem. Grounds and resistance problems can generally be tested by performing voltage drop tests which are typically be less than 0.2 volts.

Disassembly and Assembly Inspect bushings; replace as necessary.

Always check the depth to which bushings are installed and the direction of the fluid groove, if so equipped, before you remove them. Many bushings that are used in the planetary gearing and output shaft area have lubricating holes in them. Be sure to line these up correctly during installation to prevent blocking off fluid delivery holes, which could destroy the gear train. If any damage is evident on the bushing, it should be replaced. Bushing wear can be checked a wire-type feeler gauge as well as checked by observing the lateral movement of the shaft that fits into the bushing. Any noticeable lateral movement indicates wear, and the bushing should be replaced. You can check this fit by measuring the inside diameter of the bushing and the outside diameter of the shaft with a vernier caliper or micrometer. This is a critical fit throughout the transmission and especially at the converter drive hub. Whenever possible, all new bushings should be installed with the proper bushing driver, but an arbor press is the tool of choice for bushing installation, especially if the bushing has a large amount of press (interference) fit into its bore. If the bushing must be driven in, a bearing knife can be used to chamfer the edge of the bushing to remove any material raised by installation.

Inspect, test, flush or replace transmission fluid cooler.

Any time that the transmission is replaced, the cooler should be flushed with an approved solvent. Back-flushing is usually suggested. If a clogged cooler is suspected check for pressure drop and flow. Install an oil pressure gauge before and after the ATF cooler, start the vehicle and observe the gauges. A blockage in the cooler will result in a large pressure difference. To check for fluid flow, remove the cooler outlet hose, start the vehicle and observe the amount of fluid that enters the can in 30 seconds and compare with manufactures spec. The pump should generally flow at least a quart in 20 seconds.

Inspect components of one-way clutch assemblies; replace as necessary.

Because they are purely mechanical in nature, one-way clutches are relatively simple to inspect and test. The durability of these clutches relies on constant fluid flow during operation. If a one-way clutch has failed, a thorough inspection of the hydraulic feed circuit to the clutch must be made to determine if the failure was due to fluid starvation. The rollers and sprags ride on an overrunning state, and any loss of fluid can cause a rapid failure of the components. Sprags, by design, produce the fluid wave effect as they slide across the inner and outer races, making them somewhat less prone to damage. Rollers, due to their spinning action, tend to throw off fluid, which allows more chance for damage during fluid starvation. During the check of the hydraulic circuit, take a look at the feed holes in the races of the clutch. Use a small-diameter wire and spray carburetor cleaner or brake cleaner to be certain the feed holes are clear. Push the wire through the feed holes and spray the cleaner into them. Blowing through them with compressed air after cleaning is recommended. Roller clutches should be disassembled to inspect the individual pieces. The surface of the rollers should have a smooth finish with no evidence of any flatness. Likewise, the race should be smooth and show no sign of brinelling, as this indicates severe impact loading. This condition may also cause the roller clutch to buzz as it overruns. All rollers and races that show any type of damage or surface irregularities should be replaced. Check the folded springs for cracks, broken ends, or flattening out. All of the springs from a clutch assembly should have approximately the same shape. Replace all distorted or otherwise damaged springs. The cam surface, like the smooth race, must be free of all irregularities. Sprag clutches cannot easily be disassembled, so a complete and thorough inspection of the assembly is necessary. Pay particular attention to the faces of the sprags. If the faces are damaged, the clutch unit should be replaced. Sprags and races with scored or torn faces are an indication of dry running and require the replacement of the complete unit. Once the one-way clutch is ready for installation, verify that it overruns in the proper direction. In some cases, it is possible to install the clutch backwards, which would cause it to overrun and lock in the wrong direction. One-way clutches are often used to provide additional holding power for clutches and bands, or to allow seamless transfer of power source between engine and vehicle (preventing planetary freewheeling for engine braking in lower ranges), and to allow freewheeling of planetary members and attached gear train (overdrive range during deceleration) to prevent engine braking, which helps fuel economy. Improper installation (backwards) can cause some strange drivability problems; therefore, a good understanding of power flow through the one-way clutch is needed for accurate diagnosis and correct transmission assembly. Improper installation would result in some definite drivability problems. To make sure you have installed the clutch in the correct direction, determine the direction of lock-up before installing the clutch. One-way clutch assemblies are sometimes the source of a noise from the transmission in a particular range or mode of operation (decelerating, etc.). This noise is usually a "buzzing" noise. Knowing the power flow of the transmission in each range will help diagnose the one-way clutch as the noise source as to whether it's in a holding (no movement between its races) or overrunning mode (suspect as noise source) of operation.

Stall test

Before performing a stall test, ensure that the transmission is warmed up and the fluid level is normal. Do not perform the stall test for more than 15 to 20 seconds to prevent overheating When performing a stall test, place the transmission in gear, hold the brake, and raise the engine's rpm. The stall speed is the highest engine speed achieved without turning the wheels. If the stall speed is below specifications, poor engine performance or slipping stator clutch is indicated. The vehicle will exhibit poor acceleration, either because of lack of power from the engine or because there is no torque multiplication occurring in the converter. If the stall speed is above specification, the bands or clutches in the transmission may be slipping and not holding properly. If the vehicle has poor acceleration but had good results from the stall tests, suspect a seized one-way clutch. Excessively hot ATF in the transmission is a good indication that the clutch is seized. If a converter makes noise, in gear, during the stall test, but not in neutral converter should be bench tested.

Torque valve body fasteners to specification.

Before reassembling a valve body, check the new valve body gasket by laying it over the spacer plate and holding it up to the light. No fluid holes should be blocked. Torque assembly to specifications to prevent warpage and possible leaks. Overtorquing can also cause the bores to distort.

Most electrical circuits are designed to operate the solenoid at 60 percent duty cycle or less most of the time.

By varying the hydraulic mainline pressure the TCM can control shift and converter clutch timing and parasitic drag of fluid pump.

Disassembly and Assembly (5 questions) Inspect shafts; replace as necessary.

Carefully examine the areas on all shafts that ride in a bushing, bearing, or seal. Also inspect the splines for wear, cracks, or other damage. A quick way to determine spline wear is to fit the mating splines and check for lateral or rotational movement. Lubricating fluid is carried through most shafts, and an internal cleaning for debris is necessary. Washing the shaft passage out with a solvent and possibly running a piece of small-diameter wire through the passage will dislodge most particles. If the shaft is so equipped, be sure to check that the ball closes off the end of the shaft is securely in place. Input and output shafts can be solid, drilled, or tubular. Small scratches can be removed with 300-grit emery paper. The splines should not show any sign of waviness along their length. If the shaft has a check ball, be certain the ball seats in the correct direction. The output shaft uses the rear of the input shaft to center and support itself. The small bushing found in the front end of the output shaft should always be replaced on these transmissions during rebuilding.

Disassembly and Assembly Check end play; inspect, measure, and replace thrust washers and bearings as needed

Check end play before disassembly for a reference measure and also to see total wear of all thrust washers. The thrust washer is to support a thrust load or axial movement and prevent of the planetary gear sets. Flat washers should also be checked for broken or worn tabs which are are critical for holding the washer in place. Plastic thrust washers will not show wear and must be measured to detect wear. If the plastic thrust washer has any metal embedded in it, the thrust washer should be replaced. Use a petroleum jelly type lubricant to hold thrust washers in place during assembly. There are special greases designed just for automatic transmission assembly that will also work. Slowly rotating the shaft, if possible, while applying side or end pressure in the caged needle bearing will find this type of wear. Needle bluing indicates lack of lubrication or overloading. Cage scuffing (shiny areas between rollers) indicates needle wear requiring replacement.

Disassemble, clean, and inspect transmission case, sub-assemblies, mating surfaces, and thread condition.

Clean outside of the trans before you disassemble. Clean parts with approved solvents. Blow dry parts and don't use rags. The lint from a rag can easily destroy a transmission after it has been rebuilt. If any play is found between the converter and the input shaft both must be replaced. Measure the transmission end play to determine the thickness of the thrust washers needed during reassembly. Excessive end play allows clutch drums to move back and forth too much, causing the transmission case to wear.

Electronic mainline pressure control will generate maximum pressure when electricity is removed. A solenoid operating at 0 percent duty cycle would cause highest transmission pressure.

Electronic mainline pressure control will generate minimum pressure when electric on time or frequency rate is highest. A pressure control solenoid operating at 100 percent duty cycle would cause low transmission pressure.

Replace fluid and filter(s); verify proper fluid level and type (for transmissions with, or without, a dipstick).

Excessive metal should be cause for alarm, and the customer should be informed. Large metal pieces usually indicate a serious problem. A black film in the bottom of the pan typically comes from the clutches. An excessive amount of clutch material indicates a worn transmission.

Disassembly and Assembly Inspect and measure transaxle final drive components; repair, replace and/or adjust as necessary.

Final drive units may be hypoid gear, helical gear, or planetary gear units. The hypoid and helical gear type should be checked for worn or chipped teeth, overloaded tapered roller bearings, and excessive differential side gear and differential pinion gear wear. Excessive play in the differential is a cause of engagement clunk. Be sure to measure the clearance between the side gears and the differential case and to check the fit of the differential pinion gears on their shaft. Proper clearances can be found in the appropriate shop manual. It is possible that the side bearings of some final drive units are preloaded with shims. Select the correct size shim to bring the unit into specifications. With a torque wrench, measure the amount of rotating torque. Compare your readings against specifications. If the ring gear carrier bearing preload and case gears' end play are within spec and the bearings are in good condition, the parts can be reused. However, always install new seals during assembly. It should be noted that these tapered roller bearings function the same as RWD rear axle side bearings and the preload of reused bearings should not be set to the preload specifications for a new bearing. Used bearings should be set to the amount found during teardown or about one-half the preload of a new bearing. Planetary-type final drives are also checked for the same differential case problems that the helical type would encounter. The planetary pinion gears need to be checked for looseness or roughness on their shafts and for end play. Any problems found normally result in the replacement of the carrier as a unit, since most pinion bearings and shafts are sold as separate parts. Again, specifications for these parts are found in the shop manual. Planetary-type final drives, like helical final drives, are available in more than one possible ratio for a given type of transaxle, so care should be taken to assure that the same gear ratios are used during assembly. This is not normally a problem when overhauling a single unit; however, in a shop where many transmissions are being repaired, it is possible to mix up parts, causing problems during the rebuild.

High fluid levels or a overheated transmission can also cause aeration.

Foaming may be evidenced by fluid leakage from the transmission's vent.

Inspect and measure fluid pump components; replace as necessary.

Inspect the pump bore for scoring on both its bottom and sides. A converter that has had a tight fit at the pilot hub could hold the converter drive hub and inner gear too far into the pump, causing cover scoring. A front pump bushing that has too much clearance may allow the gears to run off center, causing them to wear into the crescent and/or the sides of the pump body. This kind of pump wear investigation should always be followed up by a measurement of converter hub-to-bushing clearance check. If it is found to be excessive, the causes can be many. Some transmissions are fitted with "finish-in-place pump bushings," which means the final bore centerline of the bushing places the inner pump gear in the best location in the pump pocket for pressure development. This means the original factory bronze alloy bushing inside diameter and pump pocket can be offset from its outside diameter. If a remanufactured torque converter with a slightly different hub diameter (smaller) and steel alloy (softer) content is installed, problems can result from rapid wear of the converter hub due to increased clearance, allowing the pump inner gear to wander out of its original position, creating noise or low output among other problems stated in Task 1. If the OE bushing is replaced as a standard procedure, problems can now stem from relocating the inner pump gear centerline from the original pump pocket bore centerline. The stator support should be inspected for looseness in the pump cover. This can be done while you check for interference inside a torque converter. The shaft's splines and bushing should also be looked at carefully. If the splines are distorted, the shaft and the pump cover should be replaced. The bushings mounted in the hollow stator shaft supporting the turbine shaft and/or the bushings in the hollow turbine shaft supporting the internal fluid pump drive shaft, control fluid flow through the converter and cooler, and their fit must be checked. Bushings must be tight inside hollow shafts and provide the input shaft with a specified clearance. Inspect the gears and pump parts for deep nicks, burrs, or scratches. Examine the pump housing for abnormal wear patterns. The fit of each gear into the pump body, as well as the centering effect of the front bushing, controls fluid pressure loss from the high-pressure side of the pump to the low-pressure input side. Scoring or body wear will greatly reduce this sealing capability. Excessive clearance at any of these mating surfaces mentioned above, including inner pump gear/rotor-to-hub clearance, can cause or contribute to a condition known as converter drain down. Torque converter drain down occurs when a vehicle is allowed to sit for a time long enough to allow the fluid to drain back into the reservoir, leaving a low level of fluid in the converter. This void needs to be filled with fluid and the air expelled before the turbine can transmit power to the input shaft of the transmission. The time required to do this causes a delay in vehicle movement after selecting a gear, especially on those transmissions that do not allow filling of the torque converter in park. This delay is often expressed as a concern by the customer. Careful examination of these areas will correct or reduce converter drain down and prevent it from becoming a customer concern. Another important clearance to prevent the possibility of pump cavitation, also called loss of prime by some manufacturers, is pump pocket or gear face clearance. This clearance, if excessive (general rule is 0.002 in (0.05 mm) maximum), allows air to be drawn in at the neutral (zero pressure) position where the inlet porting in the pump pocket begins. When this condition occurs, the transmission neutralizes, causing momentary or complete and unexplained loss of transmission of power from the torque converter. This normally occurs when fluid temperatures are elevated, which causes reduced viscosity. That, coupled with excessive clearance, allows ambient air to be drawn in, creating the condition. On fixed displacement pumps, use a feeler gauge to measure the clearance between the outer gear and the pump pocket in the pump housing. Also check the clearance between the outer pump gear teeth and the crescent, and between the inner gear teeth and the crescent. It is equally important, if specifications are given, to accurately check the inner gear to crescent clearance. The pump should be placed on the converter hub with its bushing-to-hub and inner gear-to-drive hub clearances within specifications. This will position the inner gear close to the position that it will run in when in operation and allows the possibility of inner gear-to-crescent interference to be viewed. Compare these measurements to the specifications. Use a straightedge and feeler gauge to check gear side clearance and compare the clearance to the specifications. If the clearance is excessive, replace the pump. Variable displacement vane type pumps require different measuring procedures. However, the inner pump rotor-to-converter drive hub fit is checked in the same way as described for the other pumps. The pump rotor, vanes, and slides are originally selected for size during assembly at the factory. Changing the original size of any of these parts during overhaul can change the sizing and possibly the body of the pump. These parts are available in a range of sizes for just this reason. The vanes are subject to wear, as well as cracking and subsequent breakage. The outer edge of the vanes should be rounded, with no flattening. These pumps have an aluminum body and cover halves; any scoring indicates that they should be replaced. Inspect the reaction shaft's seal rings. If the rings are made of cast iron, check them for nicks, burrs, or uneven patterns, and replace them if they are damaged. Make sure the rings are able to rotate in their grooves. Check the clearance between the reaction shaft support ring groove and the seal ring. If the seal rings are the Teflon™ full circle type, cut them out and use the required tools to replace them. The outer area of most pumps utilizes a rubber seal. Check the fit of the new seal by making sure the seal sticks out a bit from the groove in the pump. If it does not, it will leak. The seal at the front of the pump is always replaced during overhaul. Most of these seals are the metal clad lip seal type. Care must be taken to avoid damage to the seating area when removing the old seal. Check the area behind the seal to be sure the drainback hole is open to the sump. If this hole is restricted, the new seal will possibly blow out. The drainback hole relieves pressure behind the seal. A loose-fitting converter drive hub bushing can also cause the front pump seal to blow out. Finally, pump-mating surfaces must be properly prepped and aligned before final assembly. Surface patterns near bolt holes or passages or witness marks on gaskets for pumps so equipped give indication of cross leaks that are occurring between pump halves. A honing stone can be used to take out minor dents with raised areas. Raised threads on bolt holes retaining pump halves together should be countersunk to prevent half separation during torqueing. Inner and outer gears often have alignment marks that indicate gear orientation, alignment, or rotational direction. Some inner pump gears have their drive tangs offset to indicate orientation. Some outer pump gears are oriented by the size of the radius on their outside diameter. Always study the gears before removal and if necessary, mark them with a common mark across their faces with nonremovable marker or machinist dye to ensure proper reassembly. Pump halves alignment is performed in several ways. Pumps whose covers (stator/reaction shaft support half) are the same diameter as the pump pocket body can be aligned using a large hose clamp or series of clamps or similar special tool, then using dowels to align bolt holes. Some pumps require special tools to align pump cover, bell housing, and pump body. Some pumps are equipped with alignment pins to give correct alignment. Pumps whose covers (stator/reaction shaft support) are smaller in diameter than the body are typically recessed, which aligns the two halves when bolted together. Locate the feeler gauge that best fits between the outer gear and the housing to determine gear to housing clearance. Compare the reading to the specification to determine whether or not the pump can be re-used.

1) The pressure should not drop more than 15 psi (103 kPa) between shifts. If the pressure drop between shifts was greater than 15 psi, an internal leak at a servo or clutch seal is indicated. 2) Unless the transmissions use a cutback valve that drops pressure after the vehicle attains cruising speeds. Drops greater than 15 psi will occur and are normal and many cutback valves are known for sticking and causing low-pressure under all conditions

Mainline pressure should be checked in all gear ranges and at the three basic engine speeds. If the pressures in all operating gears are within specifications at slow idle, the pump and pressure regulators are working fine. If all pressures are low at slow idle, it is likely that there is a problem in the pump, pressure regulator, filter, or fluid level, or there is an internal pressure leak. To further identify the cause of the problem, check the pressure in the various gears while the engine is at fast idle. If the pressures at fast idle are within specifications, the cause of the problem is normally a worn fluid pump; however, the problem may be an internal leak. Internal leaks typically are more evident in a particular gear range because that is when ATF is being sent to a particular device through a particular set of valves and passages. If any of these components leaks, the pressure will drop when that gear is selected or when the transmission is operating in that gear.

Diagnose shift quality concerns resulting from problems in the electronic transmission control system.

Most systems fail in one or more of these three categories. 1)The processor places the transmission in a fixed gear, a no shift condition. This condition is often called "default mode," "limp-in mode," or "hardware limited operation strategy" (HLOS2) 2)The second category the computer recognizes a problem but still controls the shift pattern. A pressure test will determine if the transmission is operating in this mode. While it is operating in this mode, line pressure will be constant and high (no line pressure rise with throttle movement). The pressure control solenoid can be operated with some scanners to deliver a programmed-in pressure that can be verified with a gauge. The solenoid control circuit can be observed with an amp probe to verify solenoid winding and pintle movement integrity while this test is performed. Manufacturers dub this category "failure mode effects management" or FMEM, "shift strategy abort," or "default action." 3)The third category is one that warns the driver with a flashing OD, S4, or Hold light. A trouble code will be stored, and the light will continue to flash as long as the problem continues. These problems are most often electrical.

Inspect accumulator and servo bores, pistons, seals, pins/pin bores, springs, and retainers; repair or replace as necessary.

On those units equipped with servos or accumulators serviced externally, carefully inspect the cover area to determine the exact cause of the leakage. Band servos and accumulators are basically pistons with seals in a bore that are held in position by springs and retaining snap rings. Cast-iron seal rings may not need replacement, but rubber and elastomer seals should always be replaced. A servo's piston may be made of either aluminum or steel. Aluminum pistons should be carefully checked for cracks and piston/guide pin bore wear. On both aluminum and steel, the seal groove should be free of nicks or any imperfections that pinch or bind the seal. Clean up these problems with a scraper or small file. The servo bore should be checked for severe scratches and localized wear areas. Minor bore scratches can be polished out, and there are bore sleeves available from manufacturers to salvage a transmission case due to severely worn servo bores, and there are oversized piston/guide pins available to repair piston wear problems. A side clearance of 0.003 to 0.005 inch (0.076 to 0.127 mm) is required.

Disassembly and Assembly Assemble after repair.

Once the transmission has been cleaned and inspected and all faulty components repaired, assembly can begin. During assembly, it is important to keep all components as clean as possible. Dirt or debris could clog fluid passages and cause valves to stick. Soak all bands and clutch discs in ATF for 30 minutes. Prelube all O-rings and seals with an approved assembly lubricant; never install a dry seal. Lube all internal components that will have metal-to-metal contact such as the bearings and gear sets. Overuse of sealers or gasket maker should be avoided if they are used at all. The excess can break off inside the transmission and clog internal passages. Be sure to refer to service information and make any necessary clearance or end play checks. These clearances are often adjusted with shims or thrust washers. Also be sure that clutch pack clearances are within spec and the bands are properly adjusted. Clutch pack clearances are typically adjusted by installing different thicknesses of snap rings or reaction plates. Many bands are adjusted with an adjustment screw or a selective servo pin. When installing the pump, it may be helpful to use guide pins and seal compressors to ease installation. Before installing the valve body, it is a good idea to air test the clutches and bands. This involves applying low-pressure shop air to the hydraulic passages of the bands and clutches. If they are in good working order, a clunk will be heard as the unit engages. A hissing noise indicates a leak in the circuit. When installing the valve body, hold all check balls in place with assembly lube and torque the valve body bolts in the proper sequence. With the transmission assembled, the torque converter can be installed. It is usually common practice to pour approximately 1 quart of transmission fluid into the torque converter before installation. During installation, be sure that the torque converter completely engages the pump. A measurement of how deep the torque converter seats into the bell housing should have been taken before removal. This measurement can be used upon installation to be sure that the torque converter is fully engaged. Failure to fully engage the torque converter can result in a damaged torque converter drive hub and/or pump.

One method of pinpointing the source of the noise is varying the pump pressure at idle with transmission in park or neutral.

One method of pinpointing the source of the noise is varying the pump pressure at idle with transmission in park or neutral.This can be further verified by watching the vibrations of an attached pressure gauge's needle. If it has no effect, then the pump has been ruled out.

Differentiate between engine performance and transmission/transaxle related problems.

One widely accepted method of determining whether a problem exists in the engine or transmission is to look at upstream oxygen sensor waveforms while the problem is occurring. If a cylinder misfire occurred and whether the misfire most likely occurred from a lean cylinder charge, insufficient spark intensity or duration, or excessive EGR flow to a cylinder(s). Check for the presence of any engine codes stored in both the manufacturer and OBD II generic side of the controller. If testing shows no signs of an engine problem, a scanner should be used to test the slippage, measured in rpm, that exists between the engine and the turbine shaft. If there is excessive slippage compared to normal slip, the rpm problem is with the transmission/torque converter.

Inspect bands and drums (housings/cylinders); replace and/or adjust as necessary.

Servicing of bands and their components includes inspection of the bands, as well as the drums that the bands wrap around. Before the introduction of overdrive automatic transmissions, most bands operated in free condition during most driving conditions. This means that the band was not applied in the cruising gear range. However, many overdrive automatic transmissions use a band in the overdrive cruise range, which puts an additional load on the band and subsequently causes additional wear on the band. For this reason, a thorough inspection of the bands is very important. It must be able to hold or provide braking action. The bands in a transmission will be either single or double wrap, depending on the application. Both types can be the heavy-duty, cast-iron type or the normal strap type. The friction material used on clutches and bands is quite absorbent. This characteristic can be used to tell if there is much life left in the lining. Simply squeeze the lining with your fingers to see if any fluid appears. If fluid appears, this tells you the lining can still hold fluid and has some life left in it. It is hard to tell exactly how long the band will last, but at least you have an indication that it is still useable. Strap or flex type bands should never be twisted or flattened out. This may crack the lining and lead to flaking of the lining. Band failure found during an overhaul is easy to spot. Look for chipping, cracks, burn marks, glazing, non-uniform wear patterns. and flaking. If any of these defects are apparent, the band should be replaced. Also inspect brake band friction material for wear. If the linings have wear, carefully check the band struts, levers, and anchors for wear. Replace any worn or damaged parts. Look at the linings of heavy-duty bands to see if the lining is worn evenly. A twisted band will show taper wear on the lining. If the friction material is blackened, this is caused by an excessive buildup of heat. High heat may weaken the bonding of the lining and allow the lining to come loose from the metal portion of the band. The drum surface should be checked for discoloration, scoring, glazing, and distortion. The drums will be either iron castings or steel stampings. Cast-iron drums that are not scored can generally be restored to service by sanding the running surface with 180-grit emery paper in the drum's normal direction of rotation. A polished surface is not desirable on cast-iron drums. The surface of the drum must also be flat. This is not usually a problem with a cast-iron drum, but it can affect the stamped steel type drum. It is possible for the outer surface of the drum to dish outward during its normal service life. Check the drum for flatness across the outer surface where the band runs. Any dishing here will cause the band to distort as it attempts to get a full grip on the drum. Distortion of the band weakens the bond of the friction material to the band and will cause early failure due to flaking of the friction lining. A dished stamped steel drum should be replaced. Check the service manual for maximum allowable tolerances.

Inspect, test, adjust, repair, or replace electrical/electronic components and circuits.

Some electronic transmissions are only partially controlled. Only the engagement of the converter and third to fourth shifting are electronically controlled. Other models feature electronic shifting into all gears, plus electronic control of the TCC. At least two shift solenoids are incorporated into the system, and shifting takes place by controlling the solenoids. The desired gear is put into operation through a combination of on and off or constantly duty-cycled solenoids with elevated ground potential to modulate flow and guard against overheating the solenoid. The shift solenoids are controlled by the control module, which either supplies power to the solenoids or supplies a ground circuit. Improper shift points can be caused by electrical circuit problems, faulty electrical components, or bad connectors, as well as a defective governor or governor drive gear assembly. Some EATs do not rely on the hydraulic signals from a governor; rather they rely on the electrical signals from electrical sensors to control a PWM (pulse width modulated) solenoid that converts line pressure to a pressure linear to road speed, which controls the timing of the shift valves. Computer-controlled transmissions often start off in the wrong gear. The default gear is simply the gear that is applied when all the shift solenoids are off, usually second or third gear and reverse to allow limp-in operation to continue driving and electronic pressure control, mainline pressure will be defaulted to a fixed high level to prevent apply clutch or band burn-up. The electrical portion of these control circuits is best checked with the circuit powered, using bi-directional testing with a scan tool and a voltage drop test. This presents an excellent opportunity for volt drop testing under maximum current demand. Check all ground straps to the frame or engine block is especially important for electronically controlled transmissions that have a lock-up torque converter.

Disassembly and Assembly Inspect case bores, passages, bushings, vents, mating surfaces, and dowel pins; repair or replace as necessary.

Special attention should be given to the following areas: the clutch, the fluid pump, the servo, and the accumulator bores. All bores should be smooth to avoid scratching or tearing the seals. Check the fit of the servo piston in the bore without the seal, if possible, to be sure it has free travel. Repair sleeves are currently available from manufacturers to prevent expensive case replacement. Imperfections in steel or cast-iron parts can usually be polished out with crocus cloth. Use a crocus cloth inside clutch drums to remove the polished marks left by the cast-iron sealing rings. This will help the new rings rotate with the drum as designed. Never use sandpaper will leave too deep a scratch in the surface. As a rule, all sealing rings, either cast-iron or Teflon, are replaced during overhaul. Although not common, porosity in the case passages can cause cross-tracking of one circuit to another. This can cause bind-up (two gears at once) or a slow bleed of pressure in the affected circuit, which can lead to slow burnout of a clutch or band. to check fill the circuit with solvent and watching to see if the solvent leaks away. If the solvent goes down, you will have to check each part of the circuit to find where the leak is. Be sure to check that all necessary check balls were in position during disassembly. Small screens found during tear down should be inspected for foreign material. Most screens can be removed easily. Some solvents will destroy the plastic screens. Low air pressure can be used to blow the screens out in a reverse direction. Vents are located in the pump body or transmission case and provide for equalization of pressure in the transmission. A clean, open passage is all you need to verify proper operation. The symptoms of a restricted transmission vent are that of a weak pump with low volume output. A simple check that can be performed is to flow check the cooler circuit while placing a slight amount of pressure through the fill tube with an air nozzle.If flow increases significantly, a restricted transmission vent is suspect.

Perform torque converter clutch (lock-up converter) mechanical/hydraulic system tests

The PCM turns on the converter clutch solenoid, which opens a valve and allows fluid pressure to engage the clutch. Some manufacturers use a pulse width modulated torque converter clutch to provide progressive lock-up and unlock. Many of the pulse width modulated converters may be applied in any forward gear. A common cause of "perceived" TCC shudder problems is an engine misfire that occurs when the converter locks up or as it is locking. Old/worn out ATF is another problem that causes TCC shudder during application is transmission fluid that is worn out. Software updates can help shift schedules and torque converter clutch strategies that were not successful in the real world. Check for TSB If the TVC cable adjustment is off, it may cause the transmission to shift early or late.

Measure clutch pack clearance; adjust as necessary.

The clearance check of a clutch pack is critical for correct transmission operation. Excessive clearance causes delayed gear engagements, while too little clearance causes the clutch to drag. Adjusting the clearance of multiple-disc clutches can be done with the large outer snap ring in place. With the clutch pack and pressure plate installed, use a feeler gauge to check the distance between the pressure plate and the outer snap ring. Clearances can also be measured between the backing plate and the uppermost friction disc. If the clutch pack has a waved snap ring, place the feeler gauge between the flat pressure plate and the wave of the snap ring farthest away from the pressure plate. Compare the distance to specifications. Attempt to set the pack clearance to the smallest dimension shown in the chart. Clearance can also be checked with a dial indicator and hook tool. The hook tool is used to raise one disc from its downward position, and the amount that it is able to move is recorded on the dial indicator. This represents the clearance. Multi-disc clutch packs have several methods of clearance adjustment. Selective (varying thickness) components are used to adjust the free movement of the clutch pack. These range from retaining plate snap rings and pressure and reaction plates to custom steel plate thicknesses usually offered in overhaul kits. If clearance is less than specified, thicker selective components are used to take up the clearance; the opposite is true if the clearance is too great. Some transmissions use tapered snap rings for additional retaining power against the hit of the reaction or pressure plate when the clutch is applied. Snap ring orientation and end location are critical to the ring's ability to hold and also to its longevity.

Disassembly and Assembly Inspect transaxle drive chains, sprockets, gears, bearings, and bushings; replace as necessary.

The drive chains used in some transaxles should be inspected for side play and stretch. Chain deflection is measured between the centers of the two sprockets. Typically, very little deflection is allowed.One manufacturer has the technician deflect the chain inward on one side until it is tight. Mark the housing at the point of maximum deflection. Then deflect the chain outward on the same side until it is tight. Again mark the housing in line with the outer edge of the chain at the point of maximum deflection. Measure the distance between the two marks. If this distance exceeds specifications, replace the drive chain. Other manufacturers' procedures vary. Be sure to check for an identification mark on the chain during disassembly. These can be painted or have dark-colored links, which may indicate either the top or the bottom of the chain. The chain should be reinstalled in exactly the same position as when it was disassembled. The sprockets should be inspected for tooth wear at the point where they ride. A slightly polished appearance on the face of the gears is normal. The running surface in the sprocket must also be checked, as the needles may pound into the gear's surface during operation. The removal and installation of the chain drive assembly of some transaxles requires that the sprockets be spread slightly apart.

Inspect components of hydraulic clutch pack assembly; replace as necessary.

The hydraulic clutch pack assembly consists of component parts such as steel plates, friction plates, hydraulic piston and bore, springs, hubs, etc. Once a clutch assembly has been taken apart, you may wish to inspect the clutch components or continue to disassemble the remainder of the clutch units in the transmission. If you choose the latter, make sure you keep the parts of each clutch separate from the others. Clean the components of the clutch assembly. Make sure all clutch parts are free of any residue of varnish, burned disc facing material, or steel filings. Take special care to wash out any foreign material from the inside of the drums and hub disc splines. If left in, the material can be washed out by the fresh transmission fluid and sent through the transmission. This can ruin the rebuild. The clutch's hub splines must be in good shape with no excessively rounded corners or shifted splines. Test their fit by trial-fitting one new clutch disc on the splines. Move the discs up and down the splines to check for binding. If they bind, this can cause dragging of the discs during a time when they should be free-floating. Replace the component whose hub caused the disc to drag during this check. Check the spring retainer; it should be free-floating, and it should be flat and not distorted at its inner circumference. Check all springs for height, cracks, and straightness. Any springs that are not the correct height or that are distorted should be replaced. Many retainers have springs attached to them by crimping. This speeds up production at the assembly line. Turning this type of retainer upside down is a quick check of spring length. Closely examine the Belleville spring for signs of overheating or cracking, and replace it if it is damaged. The steel plates should be checked to be sure they are flat and not worn too thin. Check all steel plates against the thickest one in the pack or a new one. A visual inspection starts with checking if spot scuffing or bluing is present on the plate; if it is, discard it. However, some discoloration of the plate is okay, and the plate is suitable for reuse as long as the plate is not warped. Warping can be checked by stacking the plates one on top of another and checking for gaps around the outside diameter. Be aware that some transmission's steel plates are slightly dished and others can be a wave design when checked on the inside diameter. The dish or wave shape acts as a cushion to soften the clutch application feel. Next, check for scoring and damaged drive lugs; if present, discard the plate. Most steel plates will have an identification notch or mark on the outer tabs to inform the transmission manufacturer of the identity of the supplier of the plates. If the plates pass inspection, remove the polished surface finish so the steel plates are ready for reuse. The steel plates should also be checked for flatness by placing one plate on top of the other and checking the shape on the inside and outside diameters. Clutch plates must not be warped or cone shaped. Also, check the steel plates for burning and scoring and for damaged driving lugs. Check the grooves inside the clutch drum and check the fit of the steel plates, which should travel freely in the grooves. Close inspection of the friction discs is simple. The disc will show the same type of wear as bands will. Disc facing should be free of chunking, flaking, and burnt or blackened surfaces. Discs that are stripped of their facing have been overheated and subject to abuse. In some cases, the friction discs and steel plates can be welded together. This occurs when extreme heat melts the facing's bonding and the facing separates from the disc. As the facing comes off, metal-to-metal contact is made and the disc and plate fuse together. This may lock the clutch in an engaged condition. Depending on which clutch is affected, drivability problems can include driving in neutral, binding up in reverse, starting in direct drive, binding up in second, and other problems that are not that common. If the discs do not show any signs of deterioration, squeeze each disc to see if fluid is still trapped in the facing material. If fluid comes to the surface, the disc is not glazed. Glazing seals off the surface of the disc and prevents it from holding fluid. Holding fluid is basic to proper disc operation. It allows the disc to survive engagement heat, which would otherwise burn the facing and cause glazing. Fluid stored in the friction material cools and lubricates the facing as it transfers heat to the steel plate and also carries heat away as some fluid is spun out of the clutch pack by centrifugal force. This helps avoid the scorching and burning of the disc. The clutch disc must not be charred, glazed, or heavily pitted. If a disc shows signs of flaking or if friction material can be scraped off easily, replace the disc. A black line around the center of the friction surface also indicates that the disc should be replaced. Examine the teeth on the inside of each friction disc for wear and other damage. Wave plates are used in some clutch assemblies to cushion the application of the clutch. These should be inspected for cracks and other damage. Never mix wave plates from one clutch assembly with another. As an aid in assembly, most wave plates will have different identifying marks.

Disassembly and Assembly Inspect and measure components of the planetary gear assembly; replace as necessary.

The planetary gears used in automatic transmissions are helical-type gears, like the ones used in most manual transmissions. This type of gear provides low noise in operation but makes it necessary to check the end play of individual gears during inspection. Look first for obvious problems like blackened gears or pinion shafts,this indicate severe overloading and require that the carrier be replaced. Occasionally, the pinion gear and shaft assembly can be replaced individually. Bluing of gears maybe normal condition from heat-treating during manufacturing. Excessive backlash between gears indicates excessive wear, and the unit should be replaced. The gear carrier should have no cracks or other problems. Wiggle the gear to be sure it is not loose on the shaft and to feel for roughness or binding of the needle bearings. Looseness will cause the gear to whine when it is loaded. The end play of the pinion gear should be checked by inserting a feeler gauge between the gear and carrier. Some gear sets can be disassembled and shims installed to correct improper end play. On some Ravigneaux units, the clearance at both ends of the long pinion gears must also be checked and compared to specifications. As a general rule, gear train end play gives quietest operation when end play is kept at the low end of the specification range. Some planetary carrier assemblies may contain a Torrington bearing just below the planetary gears that cannot be removed. Inspect this bearing for damage, and if faulty, replace the assembly. Many sun gears have inner bushings that should be inspected for looseness on their respective shafts. Check drums/shells that commonly fit to the sun gear closely, as they will typically be damaged in this area.

Disassembly and Assembly Check bearing preload; determine needed service.

There are three basic adjustments that are made when reassembling a unit or when a problem suggests that readjustment is necessary. 1)Adjusting the clearance two gears referred to as adjusting the backlash. 2)End play adjustments limit the amount of end-to-end movement of a shaft. 3)Preload is an adjustment made to put a load on an assembly at ambient (room) temperature during assembly to compensate for heat expansion of shafts, housings, and bearings while at operating temperature To much preload will wear gear and to little will wear shaft from deflection. Preload adjustments are normally checked by measuring turning effort with a torque wrench or a pull spring scale attached with a string wound around the component whose turning torque is to be measured. The measurement of turning effort to keep the component moving rather than the effort to start the component turning is then recorded and compared to a specification.

Perform module coding and/or programming (including adaptive learning reset); road test to confirm proper operation.

When EATs are replaced, the old values in the control module must be erased and relearned for the new transmission. If a scan tool is not available, the control module will eventually learn the characteristics of the transmission simply throughout the drive cycles of the vehicle. The manufacturer may also provide a sample drive cycle that is needed to learn the characteristics of the transmission.

Off-Vehicle Transmission/Transaxle Repair

With the transmission removed, inspect the torque converter flex plate for any cracks that may be evident. A cracked flex plate can often make a knocking noise. Before removing the torque converter, inspect the torque converter pilot and mating surface of crankshaft for wear. Excessive wear will result in an off-center torque converter and possible vibration. With the converter removed, check the pump drive hub for any wear as well as the two notches or grooves used to drive the transmission fluid pump. Any damage to these areas should result in converter replacement.

vibration changes with a change in vehicle speed

cause is probably the output shaft or the driveline

engine speed-related vibrations

caused by an unbalanced torque converter assembly, a poorly mounted torque converter, or a faulty output shaft

Noises that occur only when a particular gear is operated

must be related to those components providing that gear, such as a band or clutch.

If the noise is vehicle speed related

probable causes are the output shaft and final drive assembly.

noise is engine speed related and is present in all gears, including park and neutral

the most probable source of the noise is likely the fluid pump, but it could also could be torque converter components, input shaft and attached components, and drive chain/sprockets