Dan McCann
Technical Service Bulletins
Technical Bulletin Number TB229
August 1981
Engine Rebuilders - Engine Thrust Bearing Failure

One Cause Of Engine Thrust Bearing Failure

It has been reported that one cause of engine thrust bearing failure is the automatic transmission. It is actually the torque converter which causes theproblem.

Excessive pressures built up within the torque converter cause its shell toexpand or balloon resulting in a build-up of outward pressure on the crankshaft. This forward force, in turn, is exerted against the thrust bearing in the opposite direction for which is was designed to carry the load.

Technical Bulletin Number TB284
August 1983
Engine Rebuilders - Crankshaft thrust Failure

Crankshaft Thrust Failure In Vehicles With Automatic Transmissions

Engine rebuilders have been plagued with crankshaft thrust failures in vehicles with automatic transmissions.

The following is based on information from transmission specialists, torque converter manufacturers, engine parts suppliers and members:

1. Excessive torque converter pressure can be caused by:

Ballooning - Swelling of the torque converter.

Pressure problems can be caused by excessive heat expansion, restrictions in oil passages and malfunctioning bypass or pressure regulator valves causing the crankshaft to be forced forward in the engine. Further evidence of these problems can sometimes be diagnosed by marks on the converter housing caused by the flywheel bolts being pushed against it.

2. Spline Lock

This condition happens when the stator support and the stator assembly of the transmission are worn or damaged during normal driving conditions. When the converter is engaged it moves forward to the stator support splines. If the splines lock in the forward position causing constant pressure on the crankshaft thrust bearing, it will fail prematurely due to the dissipation of lubrication.

3. Another cause is found to be customers putting their transmissions in neutral at stops, then revving the engine, and putting the vehicle into drive. This routine puts undo pressure on the crankshaft thrust area causing crankshaft breakage.

With smaller cars, and the concern over fuel economy, the car owners are going to standard transmissions. Pay particular attention to clutch slave cylinders and master cylinders. Hydraulic failure holds the throw out bearing forward. However, misadjusted clutches are the most prevalent culprit.

4. One telltale sign of transmission related engine failure is contaminated transmission fluid.

Remember, any excessive pressure holding the crankshaft forward will void the thrust area of lubricant causing a failure.

Technical Bulletin Number TB336
December 1984
Automotive Engineers Rebuilders Association - Worn Crankshaft Thrust Bearings

Why Some Crankshaft Thrust Bearings Wear Out

Besides a clutch being out of adjustment, or even a clutch petal rider, there areother reasons why a crankshaft thrust bearing wears out. One of the causes of aworn out thrust bearing is a worn out or faulty torque converter. The main purpose of the torque converter is to multiply effective engine power to the transmission at low speeds, and to act as a fluid coupling at higher speeds in delivering torsional force from the engine to the transmission main body.

The problem generally stems from a worn stator assembly, which is either allowing too much end clearance, or the one way roller clutch is not holding. Thus, the stator is freewheeling between the turbine fins inside of the converter, causing excessive slippage. The stator is the element in a torque converter which must remain stationary, in order that the flow of fluid is redirected in an efficient manner from the primary pump to the turbine and back at lower speeds, thereby increasing torque, or power output. Its function is to redirect fluid flowbetween the pump and impeller, giving proper torque multiplication from the engine to the transmission.

When the stator wears and allows more than .050" to .060" end play, the multiplication of the converter becomes more difficult due to pressure loss in the converter, and then puts more torque load on the engine or forward pressure on the crankshaft. When there is constant or too much pressure on the crankshaft thrust bearing, the oil film becomes destroyed, and the wear pattern begins. Oneof the first indications that the converter is wearing is a sluggish acceleration of the vehicle, especially on take off.

Technical Bulletin Number TB415
January 1987
Automotive Engineers Rebuilders Association - Crankshaft Thrust Bearing Failures

Crankshaft Thrust Bearing Failures

Crankshaft thrust bearing failure on vehicles equipped with automatic transmissions have mystified the engine and transmission rebuilding industries for quite some time. AERA has attempted to address these failures with technical bulletins as early as 1981. AERA bulletin numbers TB 229, TB 284 and TB 336 have all discussed these failures from different viewpoints.

Greg Boehm of Valley Transmission in El Cajon, CA with the assistance of Ed Hale have documented results of their investigation into the causes of crankshaft thrust bearing failures. AERA would like to extend its thanks to them for sharing their findings with us.

Early AERA bulletins attempt to relate the failure of crankshaft thrust bearings with the torque converter, but replacement of the torque converter does not always solve the problem. Similarly, replacement of the complete transmission or the crankshaft and bearings does not always solve the problem either.

Using a device that incorporated a port-a-power with a pressure gauge and a throw-out bearing, tests were performed on a V8 engine with a failed thrustbearing and a THM 350 General Motors transmission. It was determined that excessive forward pressure was being placed on the thrust bearing (150 to 300lbs.). After disconnecting the torque converter, the pressure dropped to zeroand the crankshaft would run wherever positioned by the fixture with no forward pressure registering on the gauge.

Replacement of the torque converter, stator support, and input shaft did not reduce the forward pressure exerted on the crankshaft. Other areas of the transmission were checked, replaced or modified in an attempt to reduce the forward pressure on the crankshaft to no avail.

Pressure gauges were finally hooked up to the transmission cooler lines. The transmission output line (converter fill) had 100 lbs. Of pressure while the return line (lube oil) only had 10 lbs. This indicated a restriction in the cooler or lines to the cooler. Bypassing the cooler substantially reduced the forward pressure on the crankshaft. Further tests indicated a positive relationship between lube oil/converter pressure and forward pressure on the crankshaft. Reducing the lube oil/converter pressure to 30 lbs. At full throttle reduced forward pressure on the crankshaft to nearly zero.

It is believed that excessive lube oil/converter pressure builds up between the front pump and the hub of the converter creating excessive forward pressure on the crankshaft. The bypass valve generally cannot vent this excessive pressure.

The AERA Technical Committee advises the following steps be taken when thrustbearing failure occurs:

1. Attach pressure gauges to the cooler lines to compare inlet and outlet pressures. They should be very close to the same reading and be in the 20 to 30 lb. Range.
2. If the cooler inlet pressure is substantially higher than the outlet pressure, investigate for any restrictions in the lines or the cooler.
3. If the line pressure is within specifications, the transmission should be checked for spline wear on the input shaft which may be causing bind and not allowing the converter to properly move rearward on the input shaft. Other areas of the transmission should be checked that directly contribute to relieving pressures and/or building excessive pressures.

In addition to the mechanical items above that can be corrected, the vehicle owner should be advised to avoid lugging the engine in high gear, and to avoid prolonged climbing of hills in high gear especially with heavy vehicles or whiletowing trailers, other vehicles, etc. Working the engine and transmission hard in high gear dramatically raises the lube oil temperature which can lead totransmission failures that may increase pressures on the converter. It is best to manually shift the transmission into a lower gear to decrease wear and tear on the transmission.

Technical Bulletin Number TB608
December 1989
Automotive Engineers Rebuilders Association - Crankshaft Thrust Bearing Failure W/Manual Transmissions

Crankshaft Thrust Bearing Failure With Manual Transmissions

AERA members have reported several instances of premature crankshaft thrust bearing failures on vehicles equipped with manual transmissions. At times this symptom is followed by low oil pressure complaints or complete main and rodbearing failure.

Inspection of the affected engine should be completed before the engine is removed from the vehicle. Check for proper clutch pedal clearance. An improperly adjusted clutch with insufficient free play will cause excessive pressure against the crankshaft thrust bearing.

Check for misalignment of the pilot bushing or bearing and pilot shaft. Improper alignment may prevent the bell housing from engaging properly with the cylinder block. The transmission bell housing should mate to the cylinder block freely. If it is required to draw the bell housing to the cylinder block using bolts,chances are a misalignment has occurred. Again, misalignment of these components will cause excessive thrust pressure against the crankshaft thrust bearing, resulting in premature failure.

Failure can also be the result of an off-center bell housing. Check the housing run-out with a dial indicator. Correct any run-out error according to manufacturer's recommendations.

Whenever you are investigating premature crankshaft thrust bearing failures, it is important to verify the movement of the crankshaft by using a pry bar or other suitable tool. If an alignment problem exists, there should be some resistance when moving the crankshaft toward the transmission. When pry bar pressure is removed the crankshaft will most likely come to rest as far forward, away from the transmission, as possible. After the excessive pressure is removed and/or the misalignment corrected, the crankshaft should be able to be moved easily in either direction.

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