Crankshaft end play and thrust bearing - why I asked the question in the first place
08-16-2015, 09:57 AM
#31
Drifting
My bad...see Dave's response.
Correction: I incorrectly stated that Greg Brown had observed driveshafts lengthening from repeated twisting. Dave's response is a clearer and succinct description of circumstances that can lead to forces that can lead to TBF.
Last edited by Captain_Slow; 08-21-2015 at 08:54 AM. Reason: Corrections
08-16-2015, 09:26 PM
#32
Former Vendor
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I don't believe Greg Brown said the drive shafts have stretched out and lengthened.
This is not what I have seen from the years we have rebuilt torque tubes and measured the drive shafts to make sure they were within specs. As far as length they all were good, both 5 speeds and automatics.
My understanding of what Greg Brown said is they have become weaker and will twist more readily.
If I'm mistaken he can clear it up.
Mark A. has been rebuilding torque tubes longer than anyone and it would be interesting to hear from him if he has seen any drive shafts lengthened by use and age.
Cheers,
This is not what I have seen from the years we have rebuilt torque tubes and measured the drive shafts to make sure they were within specs. As far as length they all were good, both 5 speeds and automatics.
My understanding of what Greg Brown said is they have become weaker and will twist more readily.
If I'm mistaken he can clear it up.
Mark A. has been rebuilding torque tubes longer than anyone and it would be interesting to hear from him if he has seen any drive shafts lengthened by use and age.
Cheers,
08-16-2015, 10:39 PM
#33
Rennlist Member
My thoughts .....
For the shaft to pull out of the rear (as they do), and the front (as they do), it would seem likely that the shaft dynamically shortens as it twists during max torque events. It would also seem reasonable to assume that the magnitude of that dynamic shortening would increase, as they become older and fatigue, and therefore the possibility of pull out from the front, or rear, or both clamps, would increase. The 'pullout' from one or both clamps is what results in 'lengthening' of the whole assembly of shaft and clamps, which results in overall forward thrust on the crank.
08-17-2015, 07:20 AM
#34
Rennlist Member
Thread Starter
Dave, you may have missed this 
:
:...However, if the front clamp is loose, the driveshaft will pull out of the flex plate when it shortens, and when it returns to normal length, will push the flex plate forward, reducing the end play of the crank shaft, and after sufficient iterations, finally push the crankshaft against the thrust bearing.
If the rear clamp is loose, the driveshaft will similarly pull out of the rear clamp, causing the rear pinch bolt to distort as the drive shaft contracts, and allowing it to ride up on the splines of the shaft.
So really, either pinch bolt can cause TBF.
If the rear clamp is loose, the driveshaft will similarly pull out of the rear clamp, causing the rear pinch bolt to distort as the drive shaft contracts, and allowing it to ride up on the splines of the shaft.
So really, either pinch bolt can cause TBF.
08-17-2015, 07:53 AM
#35
Rennlist Member
Thread Starter
Dave, I should add that in no way do I take credit for identifying the drive shaft twist as the fundamental reason for the change in length of the drive shaft assembly, or really, for any other observation I made. I just put the thoughts of others together in a way that made sense to me.