Nicholbry

I recently discovered Thrust Bearing Failure on my 1990 S4. The hunt is on for a replacement engine and is the topic of another thread here. The PO didnt' service the pinch collar so.........

Anyway, I wanted to ask a different question in an effort to better understand and to better service my driveshaft to avoid a future catastrophe. It is my understanding that the driveshaft has two pinch collars; one at the flywheel (of course) and another at the other end. Am I correct?

If so, what is the procedure for checking this pinch collar at the back end and what is the recommended torque value for it? When servicing it, should the other end be released simultaneously. I recently relieved the small increment of stress at the flywheel and retorqued to 66ft# as recommended. Perhaps this rearward collar is discussed on Rennlist as well, but my search yielded only the the foward pinch collar info. Thanks!

Bill Ball

There is no procedure to service the rear pinch bolt. The bolt's location is fixed by a slot in the shaft, so just make sure it is tight. 59 ft lbs.

John Struthers

Out of curiosity...
You loosened the the allen pinch bolt, relieving the forward shaft pressure against the crank to reduce the crank walk and machining of the bearing supports by the crank journals ... right?
What for, if the engine is hosed?
I suppose you could still start and run her. I wouldn't run her at all. But if you do keep the RPM's low or you might lose more than the bottom end.
Did you use the 2 part loc-tite when you re-torqued?
The bummer about crank walk is when the owner discovers how - relatively - easy it is to inspect for for the condition.
I might add, this is a condition that should never have come gratis with a 34K to 90K car in the first place.
Good Luck on the swap.

Black Sea RD

Hi Nicholas,

Bill is correct about the rear pinch bolt. The biggest problem is installing it correctly so it will not loosen and allow for the driveshaft splines to strip in the coupling sleeve of the torque converter flexplate.

FYI, the relieving of pressure and re-torquing the front pinch bolt to 66 foot pounds has not been found to work in our tests. Once the front OE flexplate clamp has been stretched it will not grip the driveshaft as it should even with the higher foot pound rating of the clamping bolt.

As we have said before, the higher foot pound rating was to be used in concert with a new front flexplate. Bottom line is the OE clamp is not up to the task of clamping the driveshaft well enough.

That's why we designed the replacement front flexplate clamp. Much better in clamping ability, can be released and clamped with no degrading of clamping ability, and is easily installed and set when doing a torque tube change or engine change.

This last statement is not for you Nicholas, but seeing another post I have to say this:

I personally wish the use of loctite would stop being discussed/used as one of the "recommended" methods of trying to stop the driveshaft creep. It's not a complete gaurantee it will work as advertised, is difficult to reposition the driveshaft if it doesn't work and creates a lot more trouble when doing future maintenance when the driveshaft and flexplate need to be disengaged. Ask an engine builder, driveline engineer, transmission rebuilder what he/she thinks of having someone take a torch to the front flexplate attached to the flywheel (and ultimately the crankshaft) to heat it up to the recommended temperature (with a lot of heat soak to other parts of the driveline) and then taking a mallet to that area and whacking the front flexplate clamp to get it off the driveshaft. The abuses the engine bearings, torque tube/torque converter bearings and transmission parts will take are significant and very possibly damaging. This is not meant to embarrass anyone or try to sell more of our clamps. It comes from someone who wants to keep the 928s around for years to come.

Best of luck with your project,
Constantine

Mrmerlin

If anyone is going to service the driveshaft, they should check the condition and torque, of both the front and rear clamping bolts.If you have done the front pressure relief and on a recheck it has moved then this is a signal that all may not be well with the rear clamp bolt.
It is true that there is a cutout in the drive shaft for the rear bolt to pass through the rear clamp but this cutout is not a precision fit and is capable of some movement fore and aft, if the rear bolt is not torqued to the new factory setting of 66ft/lbs, there is a possiblity that this fitting can move, While servicing torque tubes (IE for rebuild and or trans removal ) I have encountered more than a few situations where the front clamp bolt is tight and the rear though tight was no where near the correct torque and as so it was slowly moving and the result was that the shank of the bolt was grinding itself on either the front or the rear set of splines cut into the driveshaft, this made the bolt junk due to the shank having cuts in it and also made the splines in the drivesfat somwhat difficilt to slide out of the coupler, due to a slight mushrooming effect from rubbing on the bolt. Anyway Constantine has new front clamp that seems to stop drivshaft creep, but this new clamp or the factory part will only be as good as the clamping of the rear bolt . So if you check the front you should also check the back atleast once, install a new bolt and use blue locktite on the new bolt and torque to 66ft/lbs. If your having trouble with the rear coupler lining up you can move the driveshaft front or back by working at the front and tapping on the front clamp, the driveshaft should be able to be moved in either direction to put the slot in the driveshaft in the correct postion in the rear clamp. I did this on my car and few others (66ft/lb and blue locktite on the new bolts ONLY) and in checking have had no movement issues my car has been checked 2 times and covered 10,000 miles, and the front clamp has stayed put IE no movement detected. Just to clarify the use of blue locktite is to be put on the new clamping bolts, if its used on the coupler to driveshaft then you run the risk of not being able to seperate them when it comes time to either remove the torque tube or trans..... Goodluck, Stan

John Struthers

While you are opining Constantine... You might have mentioned a new pinchbolt ... not necessarily your idea of a fix but.....
Point taken with a caveat.
If the locktite in conjunction with a NEW pinchbolt does work and you don't beat your 928 like a rented mule there should be NO REASON to remove/loosen it again in the forseeable ownership of the car, particularly, if one was bright enough to install a re-built tt while they were under there.
Point of fact, yes Loctite on a new part/set of parts CAN be a bugger to remove. And that's with the assumption it wasn't outdated, and mixed/applied properly.
Point of fact, Loctite on used parts is USUALLY easier to remove.
But the real issue here, from my point of view, remains the same.
How much damage was done to the crank bearing supports and mains/ how far did Nicholas' crank walk?
Has it bumped the mains?
Why is it running if as he say's in the 1st sentence...failure.
The body of his post is a query on proper inspection/service of the front and rear clamp.
But, the last 5 lines of his post indicate that he broke torque to relieve forward pressure on the crank, the re-torqued to 66 ft lbs (lb ft). Did he push back against the TT?
I'm kind of wondering if he actually measured the 'kickback' and if there was any damage at all.
My point is that if he has main bearing problems it shouldn't be running, or, he may have NO PROBLEM other than a 'Little walk'. in which case he doesn't need an engine.
At the same time, if he doesn't need an engine and the TT is OK, why not loctite until he decides to procure your FIX?
BTW
We all have opinions ... on loctite, yours and mine don't converge and both have merit.

Bill Ball

Hey Stan:

Where is the 66 ft lbs from? I know some people do it, but the WSM section written in 1992 says 59 for the rear and I never felt a need to change it. Frankly, I don't do the front to 66 either as I don't think it makes any difference; the clamp is still going to move and needs to be checked periodically.

Nicholbry

J.Struthers, thanks for your reply to my post. I tried to answer a few questions for you and commented on others to help you and others understand my situation better.
I plan on driving it a bit to correct my ride height. I've made an adjustment, but still have to settle the chassis and tidy up the settings. Also, my mechanic is 1 hour away so a trip will be necessary as soon as I locate an engine or block.
Since a new engine will be dropped soon I didn't loctite. Curious though, "2 part". What's that about? I wasn't aware of a 2 part type.
I agree. I couldn't believe that the PO let this happen. I'm the 3rd owner. The first likely knew, but the 2nd apparently didn't. When the flexplate was inspected it had cracked from the pressure. I've only put 1500 mi. on her since my purchase.
Thrust Bearing Failure to mean that the thrust bearings have failed and the crank is now scouring the block. The engine hasn't stopped running yet. The car cranks perfectly when cold but hesitates once it's warm and idles low once warm.
No.
Yes, unfortunately it appears that I do need an engine. Check out the topic I posted "928 S4 Engine Needed!" It includes pics of my bottom end after removing my oil pan for the gasket and motor mount replacement. It was then that I confirmed my fear of TBF.

Mrmerlin:
Do you know how to properly do this procedure? Is there a step-by-step tutorial out there to help like the one that explains the other end of the driveshaft? Do I have to take apart the torque converter to get to it? Right now I have my exhaust removed and wanted to do what I could before putting it back on. Thanks.

Nicholbry

Oh yeh, one other thing. I realize that the torque tube is traditionally rebuilt/replaced with the transmission out, but can it be done with an engine removed since that side of the driveshaft is mostly free/clear or does the transmission still need to come out?

Mrmerlin

First the 66ft/lb was issued in TSB from Pcars i dont have the copy but was informed about it here, and we may also have had more info at the shop.
To work on the rear clamp bolt the exhaust needs to come off from the manifolds as they should already be loose from dropping to inspect the front, DONT FORGET to open the CE panel and disconnect the O2 seansor wires and feed it through the transmission tunnel, also the center heat shield and the right front heat shield (To gain access to the O2 wires) need to be removed. The rear clamp bolt is found by looking AT the bottom of the Torque tube about 4 inches from where it bolts to the trans bell housing, there may be a rubber plug in the t tube remove the plug and then remove the bolt you will need a helper to turn the crank to the correct position, if you see a orange colored dust around this coupler then it indicates that it is moving in the clamp, this is ground metal from the splines and or the bolt passageway. When the bolt is loose it should drop out if not , go to the front clamp and give it a few taps either forward or rearward, the bolt should drop out, this tapping moves the driveshaft in the t tube so to add clearance to the rear bolt, if the bolt has grooves cut into the shank it is a sure bet that the clamp was moving on the driveshaft, try to tap the front clamp to center the rear clamp to driveshaft groove, install the new bolt with some blue loctite and torque to 66ft/lb, then unscrew the front bolt and press the crank all the way to the rear of the car retighten the front clamp, then install the heat shields and the exhaust and O2 wire connector in the CE panel

The torque tube can be removed with the trans in place you need to remove the vacuum line and bowden cable from the trans after removing the engine

Nicholbry

If I understand you correctly, what I'm trying to do here is to force the driveshaft in the torque tube further back so that the clamp can be lined up at the rear for the bolt replacement if movement is discovered; correct?

This tapping of the front clamp...are you advising me to use a hammer (or something??) and tap the actual clamp on the driveshaft at the flywheel?

Thanks

Black Sea RD

Hi John,

[QUOTE=John Struthers]While you are opining Constantine... You might have mentioned a new pinchbolt ... not necessarily your idea of a fix but.....

Not really opining, just talking from experience. We conducted tests about the whole issue of using a new pinch bolt and torquing to the higher setting. It did not do anything to stop the amount of force needed to move a driveshaft portion through the OE clamp. Same amount of PSI rating as a old pinch bolt.

Point taken with a caveat.
If the locktite in conjunction with a NEW pinchbolt does work and you don't beat your 928 like a rented mule there should be NO REASON to remove/loosen it again in the forseeable ownership of the car, particularly, if one was bright enough to install a re-built tt while they were under there.
Point of fact, yes Loctite on a new part/set of parts CAN be a bugger to remove. And that's with the assumption it wasn't outdated, and mixed/applied properly.
Point of fact, Loctite on used parts is USUALLY easier to remove.

Using loctite is not a good thing in the front flexplate coupler as a means to stop driveshaft movement, period. Installing rebuilt torque tubes is a great idea but not often done. There have been cases when a rebuilt torque tube needs to be replaced within a warranty period. There will come a time when the drive shaft will have to be loosened from the front flexplate clamp and it will not be easy. Those that have done it have not had a good time and it was not easier and the loctite was used on used parts. There have also been cases when the driveshaft did move and could not be repositioned.

So John, do you have a vested interest in loctite? Have you done any tests on this topic?

Regards,
Constantine

Black Sea RD

Would like to see the Porsche TSB on this topic. Can you find it?

Regards,
Constantine

[QUOTE=Mrmerlin]First the 66ft/lb was issued in TSB from Pcars i dont have the copy but was informed about it here, and we may also have had more info at the shop.

Black Sea RD

Hi Nicholas,

All this information can be found in the Porsche manuals. In the manuals Porsche gives exact measurements at the transmission end of the torque tube for the proper setting of the driveshaft so it will fit into the cutout portion of the trans coupler. The manuals do say the driveshaft can be re-positioned with light taps from a hammer. But this is with the torque tube out of the car before installation. Not easy to do with the torque tube already installed.

If you are planning to do more work in this and other areas, do yourself a big favor and get the Porsche manuals for this car and read them. Tons of great information and from the source. The manuals have also been reduced to CDs by a fellow Rennlister and can be purchased from him.

Kind regards,
Constantine

Mrmerlin

well before you do any tapping the front clamp remove the rear bolt and look at the connection see where the driveshaft groove is in relation to the trans coupler, if its properly spaced no tapping is needed. IOTOH tapping is needed tap lighlty on the front clamp this will move the driveshaft a small amount either front or rearwards.... Constantine I dont have a copy of this paper,their solution was to add 10% to the original clamping torque IE 66ft/lb from 58ft/lb I seem to remember it was issued to deal with the thrust bearing failures, and the thinking was that increasing the torque of the clamp bolts would stop the shaft from moving, but the real deal is that even if the front clamp bolt is tight if the rear bolt isnt then the driveshaft will be easier to move and thus make it easier to have TBF