Help, I keep breaking flex plates!
05-07-2010, 03:30 PM
#31
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My 82 5 speed broke the center splines out of the clutch disk twice. The car had been hit in the front, it had moved the motor and this bend the flange that mounted the bell housing to the troque tube such that the clutch disks were not quite a right angles to the drive shaft. I bought a used torque tube only to discover that the flange was bent on it too. So I ended up taking a hand file an milling the flange square with the drive shaft. Never had trouble again. It does not take much misalighment of the disk/plate relative to the drive shaft to make things very unhappy.
05-07-2010, 06:40 PM
#32
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My 82 5 speed broke the center splines out of the clutch disk twice. The car had been hit in the front, it had moved the motor and this bend the flange that mounted the bell housing to the troque tube such that the clutch disks were not quite a right angles to the drive shaft. I bought a used torque tube only to discover that the flange was bent on it too. So I ended up taking a hand file an milling the flange square with the drive shaft. Never had trouble again. It does not take much misalighment of the disk/plate relative to the drive shaft to make things very unhappy.
05-07-2010, 06:57 PM
#35
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I have seen somthing like this once before when the torque was bent but it broke the shaft. Take your hands and feel the tube for any buckles.
05-07-2010, 07:29 PM
#36
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05-07-2010, 08:09 PM
#38
My quick 2 cents worth.
The torque tube bearings may have migrated aft or you may have a bent drive shaft, so +1 to Mrmerlin suggestions.
Generally we can say the the engine erives the car via a series of controlled explosions within the cylinders (combustion of fuel within the cylinders give a sharp increase in pressure within the cylinder on the compression/firing stroke).
As the engine is an 8 cylinder 4 stroke internal combustion engine it imparts 4 induced torque related harmonic vibrations into the drive shaft 4 times per revolution. The harmonic balancer at the front of the crankshaft varies to length of the crankshaft and drive shart sufficiently to detune these induced vibrations to acceptable level by a slight movement of the induced vibration nodes, hence the name of harmonic balance .
If the torque tube bearing have migrated this has changed the harmonic induced vibration nodes and the harmonic balancer will not be able to controlor reduce these excessive vibrations.
These vibrations can cause excessive out of alignment fluctuations at the forward flexplate, similar to a spinning top when is begins to loose it gyroscopic stability as its speed reduces.
The flexplate is designed to absorb forward axial movement of the drive sharft due to crankshaft end play and drive shaft torquel wind up during acceleration, not the fluctuations imparted by the higher order of induced harmonic vibrations from the firing strokes of the engine into a longer unsupported drive shaft caused by migrating bearing towards the rear of the torque tube.
Hence the suggestion to solve the initial problem which appears to be in the Torque Tube. Keep in mind Constantine's TT bearing and also his super clamp as these are recognised as the best currently available.
With regards to the locktite used, check the technical specifications for the grade of locktite on their web site and it will give you the instructions on how to release the forward clamp. My flexplatte clamp is held in place by Locktite 259 IIRC and heat is the method to release it. The Tech Specification will give the order of heat required to release.
When using heat be very aware to the safety precautions required regarding fire and working under a suspended load whether on jack stands or a lift.
Tails 1990 928S4 Auto
The torque tube bearings may have migrated aft or you may have a bent drive shaft, so +1 to Mrmerlin suggestions.
Generally we can say the the engine erives the car via a series of controlled explosions within the cylinders (combustion of fuel within the cylinders give a sharp increase in pressure within the cylinder on the compression/firing stroke).
As the engine is an 8 cylinder 4 stroke internal combustion engine it imparts 4 induced torque related harmonic vibrations into the drive shaft 4 times per revolution. The harmonic balancer at the front of the crankshaft varies to length of the crankshaft and drive shart sufficiently to detune these induced vibrations to acceptable level by a slight movement of the induced vibration nodes, hence the name of harmonic balance .
If the torque tube bearing have migrated this has changed the harmonic induced vibration nodes and the harmonic balancer will not be able to controlor reduce these excessive vibrations.
These vibrations can cause excessive out of alignment fluctuations at the forward flexplate, similar to a spinning top when is begins to loose it gyroscopic stability as its speed reduces.
The flexplate is designed to absorb forward axial movement of the drive sharft due to crankshaft end play and drive shaft torquel wind up during acceleration, not the fluctuations imparted by the higher order of induced harmonic vibrations from the firing strokes of the engine into a longer unsupported drive shaft caused by migrating bearing towards the rear of the torque tube.
Hence the suggestion to solve the initial problem which appears to be in the Torque Tube. Keep in mind Constantine's TT bearing and also his super clamp as these are recognised as the best currently available.
With regards to the locktite used, check the technical specifications for the grade of locktite on their web site and it will give you the instructions on how to release the forward clamp. My flexplatte clamp is held in place by Locktite 259 IIRC and heat is the method to release it. The Tech Specification will give the order of heat required to release.
When using heat be very aware to the safety precautions required regarding fire and working under a suspended load whether on jack stands or a lift.
Tails 1990 928S4 Auto
05-07-2010, 09:42 PM
#39
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All great responses and nothing more we can add except to make a statement that the TT internals are really getting old by now and these types of problems will become more common place. This is exactly why we went ahead and made our Super Bearings to take care of these upcoming issues.
We would suggest for all 928 owners to check the location of their TT bearings at least once a year at the front and rear to check for any changes in their locations.
Bearing migration can cause a lot of havoc with the drive line. Not sure if this is what's causing the flexplates cracking on this thread, but definitely worth a check.
Cheers,
We would suggest for all 928 owners to check the location of their TT bearings at least once a year at the front and rear to check for any changes in their locations.
Bearing migration can cause a lot of havoc with the drive line. Not sure if this is what's causing the flexplates cracking on this thread, but definitely worth a check.
Cheers,
05-07-2010, 10:46 PM
#40
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All great responses and nothing more we can add except to make a statement that the TT internals are really getting old by now and these types of problems will become more common place. This is exactly why we went ahead and made our Super Bearings to take care of these upcoming issues.
We would suggest for all 928 owners to check the location of their TT bearings at least once a year at the front and rear to check for any changes in their locations.
Bearing migration can cause a lot of havoc with the drive line. Not sure if this is what's causing the flexplates cracking on this thread, but definitely worth a check.
Cheers,
We would suggest for all 928 owners to check the location of their TT bearings at least once a year at the front and rear to check for any changes in their locations.
Bearing migration can cause a lot of havoc with the drive line. Not sure if this is what's causing the flexplates cracking on this thread, but definitely worth a check.
Cheers,
Ive been hoping you would read this thread, I understand you are the torque tube zen master. Tonight I measured the distance of the front TT bearing. It measured 11" from the front of the TT, is that acceptable?
Troy,
05-07-2010, 10:58 PM
#41
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Tails,
Thanks for your insight...as I posted to Constantine, the bearing measures 11" form the front of the tt and as I have explained to Tom at 928int today, there is no vibration what so ever at idle, running very smooth which would seem to rule out the shaft being bent... what are your thoughts?
Cheers,
Troy
Thanks for your insight...as I posted to Constantine, the bearing measures 11" form the front of the tt and as I have explained to Tom at 928int today, there is no vibration what so ever at idle, running very smooth which would seem to rule out the shaft being bent... what are your thoughts?
Cheers,
Troy
05-08-2010, 12:42 AM
#42
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Troy,
Don't replace anything until you've found out what's causing the problem.
Front dimension sounds about right .. what about the rear? Once you've checked your rear bearing position is OK you'd be able to do a run out check on your shaft at the front with a dial gauge to check for bend. If there's a bend that's affecting the flex plate then it has to show up as run out at the front. If you remove the flex plate and clamp you can do a run out check in the pinch bolt groove or the smooth section behind that. I think you're less likely to see run out while the plate and coupler are in place.
While you have the plate and coupling out you'll also be able to check your crank end float and flywheel run-out. You need to narrow down your possibilities by ruling things out one at a time by checking and measuring. Some things, like flywheel run out, you would think are really unlikely, but it's easy to cross possibilities like that off the list with a simple check measurement while you're at it. Crank end float would also seem highly unlikely, because that movement would affect the plate uniformly, but it's a check that you need to do before setting up your flex plate again, so you may as well.
You would think that a shaft bend would show up as a minor vibration at low revs and there would be a linear increase in severity with increase in revs. The fact that you have no vibration at idle, however, doesn't really rule out a damaging harmonic occurring somewhere else in the rev range.
Don't replace anything until you've found out what's causing the problem.
Front dimension sounds about right .. what about the rear? Once you've checked your rear bearing position is OK you'd be able to do a run out check on your shaft at the front with a dial gauge to check for bend. If there's a bend that's affecting the flex plate then it has to show up as run out at the front. If you remove the flex plate and clamp you can do a run out check in the pinch bolt groove or the smooth section behind that. I think you're less likely to see run out while the plate and coupler are in place.
While you have the plate and coupling out you'll also be able to check your crank end float and flywheel run-out. You need to narrow down your possibilities by ruling things out one at a time by checking and measuring. Some things, like flywheel run out, you would think are really unlikely, but it's easy to cross possibilities like that off the list with a simple check measurement while you're at it. Crank end float would also seem highly unlikely, because that movement would affect the plate uniformly, but it's a check that you need to do before setting up your flex plate again, so you may as well.
You would think that a shaft bend would show up as a minor vibration at low revs and there would be a linear increase in severity with increase in revs. The fact that you have no vibration at idle, however, doesn't really rule out a damaging harmonic occurring somewhere else in the rev range.
05-08-2010, 05:18 AM
#43
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Just had another thought as far as a crude check for misalignment before you do the above.
As the first step to removing your coupling and flex plate, undo the flex plate to flywheel bolts, and see if one section springs away from the flywheel more than other sections. I've always wondered whether pinch bolts could misalign the coupler slightly as it's non symmetrical clamping ... but if there's a shaft bend or misalignment you'd expect to see the flexplate running on a slightly different plane to the flywheel.
If there was such misalignment with the flywheel running true .. and the flexplate running true ... but with both on different planes then it would indicate misalignment of the TT relative to the motor.
If the flywheel runs true but the flexplate has a wobble it would indicate a bent shaft ... or a coupler that when tightened pulls the flexplate off the correct plane parallel to the flywheel plane. All the foregoing assumes that the flexplates have been flat and true and this one is too.
As the first step to removing your coupling and flex plate, undo the flex plate to flywheel bolts, and see if one section springs away from the flywheel more than other sections. I've always wondered whether pinch bolts could misalign the coupler slightly as it's non symmetrical clamping ... but if there's a shaft bend or misalignment you'd expect to see the flexplate running on a slightly different plane to the flywheel.
If there was such misalignment with the flywheel running true .. and the flexplate running true ... but with both on different planes then it would indicate misalignment of the TT relative to the motor.
If the flywheel runs true but the flexplate has a wobble it would indicate a bent shaft ... or a coupler that when tightened pulls the flexplate off the correct plane parallel to the flywheel plane. All the foregoing assumes that the flexplates have been flat and true and this one is too.
05-08-2010, 07:54 AM
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As you've already been told, the 11" is okay for the front bearing with your TT.
As far as being a Zen Master for the TT, thanks for the kind words! But really just a 928er who has spent way too much time looking at the 928 drive line, sometimes at a detriment to having more fun with my 928!
You are getting a bunch of great information from the group here. Just take your time as you look at each component of the drive line and keep an open mind. Sometimes we tend to focus on a specific reason for a failure when it's not the root cause.
Call if you have any questions.
Good luck and let us know what you find out!
Cheers,
05-08-2010, 08:00 AM
#45
Rennlist Member
Troy,
You said that there was lateral movement of the shaft within the torque tube assembly- you should have no such movement period. The automatics have two bearings- the manual tranny variants have three I believe. you can put a thrid bearing in there but I suspect it would serve no purpose.
It sounds as though you need to remove the torque tube completely and have it looked at thoroughly by someone who knows what they are looking at to detect what the problem is.
I would think lateral movement [TT beaing failure] will cause the flex plate to fail as well but then I would also think you would feel some significant vibrations either across the board or at specific resonant frequencies at least.
You should check to ensure that the shaft is running true as it spins. Heavy accident damage can cause the drive shaft to bend in front of the taper [I know this!] but the attrition it takes to cause this is enormous as in write off.
Take a look at the area in front of the taper to see if you can see any signs of metal delamination [the avatar on Bill Ball's posts]. If you see what looks like signs of axial cracking just behind the splines your drive shaft is shot. If this was the problem I would think you would have seen signs previously.
The flex plate is [or was] available separately but if it is not, then I am sure someone like Mark A can get you a good used one for modest bucks. As Constantine suggests, inspection for brearing migration is a good start on every 928 if it has not been done previously but not sure I agree with every year- I feel that is somewhat excessive- perhaps 5 yearly or if/when one feels there is an unexplained problem in that area.
Best thing you can do is get Constantine to rebuild your TT with his bearings and fit a superclamp while in there. The torque converter bearings should also be replaced periodically- do it if they have not been replaced.
The Loctite solution works and works well- period. I had no problem getting mine undone but that was with the TT off the car. You should have used Loctite 260 [the formulation recommended originally by Earl Gilstrom]. I trust you loctited the splines and not the pinch bolt threads. The loctite holds well under compression but I do not think it holds well under tension. Once the pinch bolt is released maybe it is possible to pry something into the gap in the split sleeve where the bolt passes through to open it slightly but have not tried that one. Heat is the recommended [by Loctite] solution.
The only other thing left to check for is a warped flywheel but I have never heard of that happening on an automatic 928.
Regards
Fred
You said that there was lateral movement of the shaft within the torque tube assembly- you should have no such movement period. The automatics have two bearings- the manual tranny variants have three I believe. you can put a thrid bearing in there but I suspect it would serve no purpose.
It sounds as though you need to remove the torque tube completely and have it looked at thoroughly by someone who knows what they are looking at to detect what the problem is.
I would think lateral movement [TT beaing failure] will cause the flex plate to fail as well but then I would also think you would feel some significant vibrations either across the board or at specific resonant frequencies at least.
You should check to ensure that the shaft is running true as it spins. Heavy accident damage can cause the drive shaft to bend in front of the taper [I know this!] but the attrition it takes to cause this is enormous as in write off.
Take a look at the area in front of the taper to see if you can see any signs of metal delamination [the avatar on Bill Ball's posts]. If you see what looks like signs of axial cracking just behind the splines your drive shaft is shot. If this was the problem I would think you would have seen signs previously.
The flex plate is [or was] available separately but if it is not, then I am sure someone like Mark A can get you a good used one for modest bucks. As Constantine suggests, inspection for brearing migration is a good start on every 928 if it has not been done previously but not sure I agree with every year- I feel that is somewhat excessive- perhaps 5 yearly or if/when one feels there is an unexplained problem in that area.
Best thing you can do is get Constantine to rebuild your TT with his bearings and fit a superclamp while in there. The torque converter bearings should also be replaced periodically- do it if they have not been replaced.
The Loctite solution works and works well- period. I had no problem getting mine undone but that was with the TT off the car. You should have used Loctite 260 [the formulation recommended originally by Earl Gilstrom]. I trust you loctited the splines and not the pinch bolt threads. The loctite holds well under compression but I do not think it holds well under tension. Once the pinch bolt is released maybe it is possible to pry something into the gap in the split sleeve where the bolt passes through to open it slightly but have not tried that one. Heat is the recommended [by Loctite] solution.
The only other thing left to check for is a warped flywheel but I have never heard of that happening on an automatic 928.
Regards
Fred
