Thrust Bearing Failure - Why is this happening ?
03-02-2009, 01:05 AM
#31
Racer
Stoopid Noob alert!!!
I am going to look at an 86.5 Automatic (higher than 1000 last 4 of Vin) out of state
When I asked about flex plate relief I was told it had been fitted with the circlip on the driveshaft .
Is this a legitimate conversion or BS.
Thanks guys
Joe
I am going to look at an 86.5 Automatic (higher than 1000 last 4 of Vin) out of state
When I asked about flex plate relief I was told it had been fitted with the circlip on the driveshaft .
Is this a legitimate conversion or BS.
Thanks guys
Joe
03-02-2009, 02:17 AM
#32
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Can be legitimate. 25mm thick tube was used up to '88 MY even though circlip was not installed after '85 MY at production line. All cars which have narrow shaft version installed can be retrofitted with circlip.
03-02-2009, 07:14 AM
#33
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Hi Joe,
Not a stupid question at all, quite a good one really.
When doing our initial research into this whole TBF affair we found that Porsche stopped using the circlip, bearing and washers sometime in the 1984 model year, according to the Porsche WSMs. From what we concluded, these pieces did help in not letting the drive shaft get pulled through the front flex plate clamp. The actual reason they were there was to set a pre-load between the front flex plate and flywheel after careful measurements were taken between the two. All of this information can be found in the Porsche WSMs.
For some reason Porsche discontinued their use in the 1984 model year. Why is not explained in the WSMs or anywhere else. After a review of available facts and some conversations we concluded the Porsche field techs were having problems setting the distances up correctly and customer cars were coming in with TBF issues. Due to these problems Porsche defaulted and removed the items from further use, instructing that the front flex plate clamp be clamped as the final step after a TT removal.
After the 928 S4 versions debuted, Porsche increased the size of the drive shaft from 25mm to 28mm so that it could better handle the increased torque of these engines. However they did not change the front flex plate clamp size to accommodate the 28mm size increase and chose to neck down the drive shaft back to 25mm for the splined portion to fit into the old style front clamp. Porsche also took away the drive shaft portion which could accommodate the circlip, bearing and washers on these newer drive shafts. Why they did not change the front flexplate clamp to accept the thicker drive shaft is unknown, but probably as a cost saving solution. This then brought it's own set of issues in the form of the 28mm drive shafts being prone to shearing problems at the neck down portion of the shaft.
On to your original question, if the mechanics used the Porsche WSMs and correctly set up the needed distances between the flex plate and flywheel using the correct shim thicknesses, then it should have stopped the drive shaft pullout problem.
However, it does not mitigate the potential of TBF damage that may already be in the engine. A careful measuring of the thrust bearing clearances should be done using the Porsche WSMs to ensure thrust bearing health before purchase. That's what I did when I bought my 1986.5 automatic track car with success.
Hope that helps,
Constantine
Not a stupid question at all, quite a good one really.
When doing our initial research into this whole TBF affair we found that Porsche stopped using the circlip, bearing and washers sometime in the 1984 model year, according to the Porsche WSMs. From what we concluded, these pieces did help in not letting the drive shaft get pulled through the front flex plate clamp. The actual reason they were there was to set a pre-load between the front flex plate and flywheel after careful measurements were taken between the two. All of this information can be found in the Porsche WSMs.
For some reason Porsche discontinued their use in the 1984 model year. Why is not explained in the WSMs or anywhere else. After a review of available facts and some conversations we concluded the Porsche field techs were having problems setting the distances up correctly and customer cars were coming in with TBF issues. Due to these problems Porsche defaulted and removed the items from further use, instructing that the front flex plate clamp be clamped as the final step after a TT removal.
After the 928 S4 versions debuted, Porsche increased the size of the drive shaft from 25mm to 28mm so that it could better handle the increased torque of these engines. However they did not change the front flex plate clamp size to accommodate the 28mm size increase and chose to neck down the drive shaft back to 25mm for the splined portion to fit into the old style front clamp. Porsche also took away the drive shaft portion which could accommodate the circlip, bearing and washers on these newer drive shafts. Why they did not change the front flexplate clamp to accept the thicker drive shaft is unknown, but probably as a cost saving solution. This then brought it's own set of issues in the form of the 28mm drive shafts being prone to shearing problems at the neck down portion of the shaft.
On to your original question, if the mechanics used the Porsche WSMs and correctly set up the needed distances between the flex plate and flywheel using the correct shim thicknesses, then it should have stopped the drive shaft pullout problem.
However, it does not mitigate the potential of TBF damage that may already be in the engine. A careful measuring of the thrust bearing clearances should be done using the Porsche WSMs to ensure thrust bearing health before purchase. That's what I did when I bought my 1986.5 automatic track car with success.
Hope that helps,
Constantine
03-02-2009, 07:32 AM
#34
Rennlist Member
As an owner of a 89 S4 I have been following all the TBF threads with interest but I am still a "Noobie" in all things 928. My understanding is that there is a clamp at the rear similar to the clamp at the front
and that this should be checked when you check the clamp at the flex plate end.
I hope this isn't a dumb question but if a Constantine clamp used at the flexplate end is the answer to the clamp migration problem why don't you need a Constantine clamp at the back? Standing by to be shot down in flames!!
and that this should be checked when you check the clamp at the flex plate end.
I hope this isn't a dumb question but if a Constantine clamp used at the flexplate end is the answer to the clamp migration problem why don't you need a Constantine clamp at the back? Standing by to be shot down in flames!!
03-02-2009, 07:42 AM
#35
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Brian,
No worries about being shot down in flames, another good question!
The rear portion of the 928 automatic drive shafts have a groove in them. The rear coupler found on the rear flex plate attached to the torque converter also has a slice in it and a square clamp which uses the same pinch bolt as the front clamp. The rear pinch bolt is placed through the grooved portion of the drive shaft locking the rear of the drive shaft in place upon final assembly once the transmission is placed back on the drive shaft.
As Mr. Merlin keeps warning, this pinch bolt should also be checked since incorrect installation can cause problems, such as damaging the rear splines or letting movement of the drive shaft in operation. There have been reports of the rear pinch bolt coming off (!) which is not good.
HTH,
Constantine
No worries about being shot down in flames, another good question!
The rear portion of the 928 automatic drive shafts have a groove in them. The rear coupler found on the rear flex plate attached to the torque converter also has a slice in it and a square clamp which uses the same pinch bolt as the front clamp. The rear pinch bolt is placed through the grooved portion of the drive shaft locking the rear of the drive shaft in place upon final assembly once the transmission is placed back on the drive shaft.
As Mr. Merlin keeps warning, this pinch bolt should also be checked since incorrect installation can cause problems, such as damaging the rear splines or letting movement of the drive shaft in operation. There have been reports of the rear pinch bolt coming off (!) which is not good.
HTH,
Constantine
03-02-2009, 08:07 AM
#36
Rennlist Member
Not all S4s have the updated drive shaft. I believe '88 was the cut off year. My '88 had the older version with the ciclip groove. I have installed this shim/clip kit. I think it was under $20. Greg Brown has been installing these for quite some time and has a very detailed description of this. His measurements for the shim stackup was exactly what I came up with.
03-02-2009, 08:23 AM
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Hi Mike,
Just as a clarification, the measurements should be done according to the Porsche WSMs, and I'm sure Greg Brown uses them.
Porsche made shims of different thicknesses to set the proper distance needed.
Cheers,
Constantine
Just as a clarification, the measurements should be done according to the Porsche WSMs, and I'm sure Greg Brown uses them.
Porsche made shims of different thicknesses to set the proper distance needed.
Cheers,
Constantine
03-02-2009, 08:26 AM
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03-02-2009, 08:41 AM
#39
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DR,
The superclamp appears to be robust and really well made. If I had an automatic, I'd get one.
One thing that scares me away from automatics is not knowing just what condition the thrust bearing is in....and it's not something that most owners will let you crawl under their car with wrenches and check. And I suspect some prepurchase inspectors may not understand it well either. Caveat Emptor.
Harvey
The superclamp appears to be robust and really well made. If I had an automatic, I'd get one.
One thing that scares me away from automatics is not knowing just what condition the thrust bearing is in....and it's not something that most owners will let you crawl under their car with wrenches and check. And I suspect some prepurchase inspectors may not understand it well either. Caveat Emptor.
Harvey
I agree completely. I couple of years ago I made a quick tool that allowed me to check crank play from the front of the engine. It was basically a leverage device that attached to the front lifting plate that used a long bar with a large fork to move the main pulley forward and backward to measure play. On the 928 we made it for we tested it against the traditional way at the flywheel and the results were the same. NOW, if I could just find where I put it I might consider making some for others.
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Last edited by DR; 03-02-2009 at 11:09 AM.
03-02-2009, 08:53 AM
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Feargal Sharkey,
The car pictured in your avatar appears to be a GTS. Finding a correct replacement block will be harder. In some cases of TBF the crank is ruined also. You may have to settle for a good used S4 engine until you find a correct GTS engine.
The car pictured in your avatar appears to be a GTS. Finding a correct replacement block will be harder. In some cases of TBF the crank is ruined also. You may have to settle for a good used S4 engine until you find a correct GTS engine.
03-02-2009, 09:16 AM
#41
Racer
What service...Go to bed on a Q and answer is there when I wake up!
Wonderful Fellas Thank You!
Constantine et al:... I am looking at a car from a very reputable member and am comforted to know the truth is being told. I just got wary when I read "pre 1985 cars had the clip". Will be checking measurement when I see the car.
Obviously very frequent checking or the clamp are the way to go. I am not a gambling man but a bet of $$ on a clamp to save $$$$$$$ on a motor seems more like an insurance plan.
Joe
Stoopid Noob but smarter than the average bear.
Wonderful Fellas Thank You!
Constantine et al:... I am looking at a car from a very reputable member and am comforted to know the truth is being told. I just got wary when I read "pre 1985 cars had the clip". Will be checking measurement when I see the car.
Obviously very frequent checking or the clamp are the way to go. I am not a gambling man but a bet of $$ on a clamp to save $$$$$$$ on a motor seems more like an insurance plan.
Joe
Stoopid Noob but smarter than the average bear.
03-02-2009, 11:14 AM
#42
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Hi,
Not really. You should always check to see if there is any pre-load. But with the clamp there probably won't be if it was set up correctly using the instructions that came with it.
Who did the installation, you or your tech?
Hope that answers the question,
Constantine
Not really. You should always check to see if there is any pre-load. But with the clamp there probably won't be if it was set up correctly using the instructions that came with it.
Who did the installation, you or your tech?
Hope that answers the question,
Constantine
03-02-2009, 12:09 PM
#43
Rennlist Member
Constantine,
You are correct. I did not mean to imply using just was Greg did. I did the measurements per the WSM. It is a little confusing at first, but after the discussions here on Rennlist, it is very simple to do. My comment about Greg was that the # of shims he uses is almost identical on every one he does. I think there is only one shim that is either used or not used. Sorry for the confusion. All of this data is in the archives.
You are correct. I did not mean to imply using just was Greg did. I did the measurements per the WSM. It is a little confusing at first, but after the discussions here on Rennlist, it is very simple to do. My comment about Greg was that the # of shims he uses is almost identical on every one he does. I think there is only one shim that is either used or not used. Sorry for the confusion. All of this data is in the archives.
03-02-2009, 01:22 PM
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Well then, your in good hands! 
But you should always check to see if there is load on the front flexplate just in case as part of other regular work under the car, say during an oil change. Always better to confirm there is no load on the front flexplate for piece of mind at least.
Cheers,
Constantine
But you should always check to see if there is load on the front flexplate just in case as part of other regular work under the car, say during an oil change. Always better to confirm there is no load on the front flexplate for piece of mind at least.
Cheers,
Constantine
03-02-2009, 01:26 PM
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Hi MIke,
No worries, just wanted to be extra sure for anyone else wanting to do this too.
And by the way, this is not the only method Greg Brown uses to stop front flexplate load.
Kind regards,
Constantine
No worries, just wanted to be extra sure for anyone else wanting to do this too.
And by the way, this is not the only method Greg Brown uses to stop front flexplate load.
Kind regards,
Constantine
Constantine,
You are correct. I did not mean to imply using just was Greg did. I did the measurements per the WSM. It is a little confusing at first, but after the discussions here on Rennlist, it is very simple to do. My comment about Greg was that the # of shims he uses is almost identical on every one he does. I think there is only one shim that is either used or not used. Sorry for the confusion. All of this data is in the archives.
You are correct. I did not mean to imply using just was Greg did. I did the measurements per the WSM. It is a little confusing at first, but after the discussions here on Rennlist, it is very simple to do. My comment about Greg was that the # of shims he uses is almost identical on every one he does. I think there is only one shim that is either used or not used. Sorry for the confusion. All of this data is in the archives.