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 transmission fluid.

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

The AERA Technical Committee