Crankshaft Thrust Bearing Failure with Manual Transmission
Engine rebuilders have been plagued with crankshaft thrust failures in vehicles with automatic transmission.
The following is based on information from transmission specialists, torque converter manufacturers, engine parts suppliers and members:
- Excessive torque converter pressure can be caused by: Ballooning -
swelling of the torque converter (See TB 229) 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.
- 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.
- 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 transmission. Pay
particular attention to clutch slave cylinders and master cylinders.
Hydraulic failure holds the throw out bearing forward. However,
misadjusted clutched are the most prevalent culprit.
- One telltale sign of transmission related engine failure is contaminated
Remember, any excessive pressure holding the crankshaft forward will void the thrust area of lubricant causing a failure.
The AERA Technical Committee