PINCH COLLAR and DRIVE SHAFT MOVEMENT
This page is set up to document the amount of drive shaft movement and flexplate preloading im encountering in my car.
It is becoming more and more apparent that the amount of preload on the forward flex plate is related to the health of the thrust bearing in the motor. Why and what causes thrust bearing failure is still open for discussion. We really dont have a definitive answer...BUT...many of us who own 87 and newer 928's SPECIFICALLY automatics...think that this preload is the link to thrust bearing failure that has occured in some cars.
In a nut shell what happens is as follows (my opinion).....For what ever reason, over a period of time, a load /force is built up on the forward flexplate, PUSHING it forward into the motor. Since the flexplate is connected to the crankshaft (via the flywheel) this force is being transmitted directly to the thrust bearing in the block. This undue pressure/force is causing the bearings to fail in SOME cars.
Why this happens Im not sure....but from my own undertaking i think it is related to the driveshaft slowly creeping forward in the torque tube. What causes this we ask??? Who knows? My line of thinking is that it is caused by the torque converter near the tranny swellling and expanding as it operates..or the drive shaft itself WINDING and UNWINDING under torque.. When this occurs the driveshaft slowly creeps forward.....as the convereter cools/shrinks...or the drive shaft unwinds...the shaft doesnt assume its original postion. In my mind i see a ratcheting type action.....the shaft moves forward..pressure builds up...then is never really released. This allows the shaft to be pushed forward just a little bit more each time...so on and so on. THIS IS ONLY MY THINKING!!!! The verdict is still out on this whole deal...but the fact is ....IT WOULD WARRANT ANYONE WITH 87s4 (i can only speak for my Make Model of car) to go under and check the preload on there forward flexplate and then relieve ANY pressure, and periodically repeat the process.
I recently installed a new Torque tube in my car and it has been 700 miles since the job was completed. During installation i carefully marked the driveshaft so i could monitor any movement.
WELL...after 700 miles..when i loosend the pinch collar, the flexplate and collar assembly once again MOVED AFT.....it moved appx 2mm. From the marks i had placed on the driveshaft itself you will see below that it crept forward appx 2mm. It is this 2mm of FORCE/preload that is in essence being transmitted to the Thrustbearing.
As for a cure to all this, there are a few of us out there that are trying to come up with something. For now my solution is to periodically check for ANY PRELOAD and relieve it when i can.
Below is a picture of my recent CHECK...
I used a flange on the bell housing as a reference mark (YELLOW). From this point i marked the drive shaft with a line (GREEN)....700 miles later the reference line(GREEN) had moved forward and the (RED) line became the new reference point. In another 700-1000 miles i suppose this (RED) line may move forward and i will have a new reference? This is what im trying to track.
You can also see the red paint i placed on the pinch collar and, when i loosed the bolt, how some of the paint disappeared under the collar as it slid AFT (this is what im tracking as well). from this point i have now made NEW marks and will check for preload and movement again in another 1000 miles or so.
As a you can see...my pinch collar bolt was torqued to 66ft/lbs. No loctite or any solution was used on the splines or collar.
I hope it all makes sense????
Tony
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