background: New owner exactly 30 days yesterday! very excited. Day one- drive 145 miles home..very carefully I might add. Day two- drive to store..come out of store and try to start..no go... battery seems dead. Call AAA. get a reluctant jump..car dies upon coasting. get a tow home. Put car up for remainder of nasty weather buy new battery etc. Day 30- nice weather...call mechanic and get car in for diagnosis (drive part way, get towed the rest..very weird) Im thinking fuel problems ie. brain, idle stabilizer valve or maybe MAF. Its a little unsettling but hey, part of ownership. I think..now Im really a member of the club. But I didn't expect this: Metal found in oil pan...aluminum shavings. Its very difficult to turn car over. What the hell is it. This guy is saying rebuild and I wet my pants. Any ideas or suggestions or maybe a prayer or two from the sidelines? (before anyone says buyer beware..Im extremely confident I bought the right car..Full records and not problem one) Its an 87 S4 66,500 miles and a suicidal owner...any ideas? Thanks everyone,
Brendan (praying to the 928 gods as you read)
Bad news, very bad news . The center main bearing thrust surface is probably gone . The only thing that locates the crank in the block is the thrust surface if the car is an automatic improper preloading of the flexplate at the flywheel will force the crank forward, take out the bearing, the counter weights then start to remachine the webbing in the block. If this has happened the block is ruined--not rebuildable. The engine will run until it gets hot then it seizes after a cooldown it will crank and run . I have heard of several new owners who inherited this problem . People who may be perfectly honest about most things will trade in a bad car to the auto dealers, unfortunately the car still ends up in an individuals hands Porsche was aware of a deficiency in the thrust area and increased the bearing shoulder and contact surface in 1985--It is a less than perfect fix.
Jim Bailey
928 International
jim@928intl.com
79 928 5spd
80 928 5spd
68 911 5spd
Here's the test for the crankshaft thrust "end play". You need a dial indicator mount it to the block, put
the pointer on the end of the crank then push the crank in and out . Measure the maximum movement. New bearings should read .110 to .312 mm - the maximum allowed is .40 as a wear limit. If wear is detected at this early stage the block should be rebuildable. As to the cause of this problem, it occurs on
automatics far more often. I believe it may be related to excessive preload of the front flex plate at the flywheel. Porsche at one time had a procedure to check preload when replacing the central tube later they
changed the recommendation stating it was no longer necessary to check this. This problem is not a common one. I should point out that I talk to 928 owners 9 to 10 hrs per day 5 days a week and have done so for 7 years. However, it is like the Medical Doctor--every one he sees is sick. When you see my posts just remember most people only call me when they have a problem. It does make it interesting for me when I drive my wife's 79 , or my 80. I hear every noise, feel every vibration and think of all the possible things that could be happening. In all fairness, both have been great cars, very few problems each has over 170,000 miles--
Jim Bailey
928 International
The standard way of handling end thrust on the crankshaft is to have an outward facing flange on each side of one of the main bearings, with the outer surface of each flange being a bearing surface. The mating surface of the crankshaft is finished as a bearing surface. Look at the photo on page 13-4 of the shop manual - The center bearing is the thrust bearing, and you can see the finished bearing area on the crank. The max 0.4 mm or 0.015" that Jim mentioned is the sum of the clearances on each side between the crank and the bearing - In other words, the crank should be free to slide back and forth a maximum of 0.4 mm or 0.015 ". This is shown on page 13-8.
The thrust bearings on a 5-speed car have to absorb the thrust caused by the clutch throwout bearing pushing on the pressure plate to release the clutch. Otherwise, there is normally no load on the thrust bearing.
The thrust bearings in an automatic car should have a very slight preload. The procedure for checking and adjusting this is given on pages 39-141 thru 39-143 in the shop manual.
Wally
I recently replaced my torque tube and noticed that the manual mentioned prying the flywheel to the rear to make sure that there was no load on the thrust bearing before tightening the clamp on the front of the driveshaft. I verified that the splined end of the driveshaft was moving freely in the hub of the drive plate by prying the plate slightly rearward with a screwdriver. I then pried the flywheel back, (you can hear the crank come up against the forward thrust bearing face), before tightening the clamp. It's been OK so
far.
Don Burrows
87 S 4, A/T
A mechanic up at the local Porsche dealer was telling me he had seen this MANY times and the failure is as you describe....at idle the motor just quits. It is seizing, that is why it stops.
It usually happens because some one takes out the trans and then puts it back in and FORGETS to check the clearance at the FRONT of the torque tube, they check the back but not the front and it pushes on the crank and thus pushes the crank THROUGH the block! Pretty bad deal all the way around, but some people just don't think when that put a tranny back in as to what other things might be getting pushed on....
I would love to hear if others on this list have had this problem, or if others have had a trans done and the mechanic did or did NOT check the clearance at the front of the Torque Tube.
--
James Morrison
Austin, TX
'80 Euro S GT-2 Race Car
'80 Euro S donor car
'81 Hellblaumetallic/Braun-Beige
'88 S4 Dunkelblau/Linnen PCA Parade Concours Class Winner
'92 GTS Polar Silver/Navy
'94 GTS Grandprixweiss/Classic Gray HCR Porschedillo Concours Winner
OK, dumb question of the day, what exactly is the thrust bearing?
Thx,
Charles Willis, 88S4
What we are talking about is the crankshaft main bearing in the center of engine block. Only one main bearing has shoulders on each side (the thrust surface). It is the only thing that limits the front to back movement of the crankshaft . The width of this shoulder was increased as of eng # 81 E 05344 model year 1984 this would indicate that Porsche felt there was a need to modify this bearing . Please note this issue is not a very common problem , being in the parts business we hear about all the problems ; few customers call to tell us the car is running great(maybe more should) that they have had no problems etc.
Jim Bailey
928 International
Jim,
All of these reports about driveshaft failures due to stress begs the obvious question; is there any way that the rebuilder can tell if the shaft in an exchange tube has been weakened by previous stress?
PS. Still looking for the procedure to set the drive train so that it neither pushes nor pulls the crank against the thrust bearing surface?
Don Burrows
87 S4, A/T (Parked)
The front flexplate a nearly triangular flat plate bolts to the flywheel with six bolts two at each point of the triangle (23-28 ftlbs torque ) Only then after the central tube, forward housing and engine have all been bolted together do you install the clamping screw on the center hub of the flexplate and tighten to 54-62 ft lbs. The center hub can slide freely front to back until the clamping screw is tightened. This also means it can be clamped in the wrong place. For example, when changing an engine if the flexplate were left clamped to the central tube and the replacement engine dropped into place then the 6 bolts tightened to the flywheel it may be possible to preload the flexplate - as the bolts are tightened this could be
either pushing or pulling. It may be possible when changing transmissions due to manufacturing tolerances to create pressure if the front clamping bolt is not released then retightened. The input shaft and clamp at the transmission can only be installed in one location because the clamping screw must pass through a machine groove on the drive shaft (all 5 spd shafts have grooves at both ends that make it very difficult to install improperly unless you take a drill and notch the shaft to make clearance forthe bolt). Yes, I have seen this and also have seen the drive shaft welded to the trans input shaft - Yes, welded. When changing central tube you must drop the rear suspension, remove the trans, then remove the central tube. The reassembly is the opposite which makes it very easy to tighten the clamping screw at the flex plate before the transmission is reinstalled then when the rear clamp screw is installed it will only go in when the groove is lined-up. Then the transmission bolts are tightened into place. Once again, preload is possible.
Porsche bulletin 928 group 3 3903 -9203 may 5 1992 - "any damage to the engine which has been caused by improper central tube installation is NOT a warranty matter" Remember this is the factory bulletin to the Dealers saying "If you screw it up We ain't gonna pay for it". At the risk of being "flamed" I submit that 90% of the problems we all encounter with our 928s are the result of improper service and neglect or misinformation. I have seen over 300 928s dismantled and the creative engineering is amazing but so many people try to work on the car without the service manuals, many shops do not own the manuals or the belt tension tools. If you have someone working on your 928, ask to see the tensioning tool. Just say you wonder what a $400 tool looks like or ask to look at the workshop manuals. To those who say "I can't afford to buy the manuals" you really can not afford not to. The vast majority of the questions asked on this forum can quickly be answered by the manuals, and accurately. They are "flawed" in the sense that they assume a certain level of familiarity with basic mechanical procedures but they are the only game in town. At least they are sold in the US, our laws require that if a car is sold here the manuals must also be available, that is not true in most other countries.
Jim Bailey
928 International
jim@928intl.com
Thanks for the response. When I reassembled my drive train I made sure that the drive shaft was free in the front flex plate splined hub by prying the plate away from the flywheel a little bit and observing that the hub slid on the splines. The part that I am unsure of in the reassembly is that, assuming that the torque converter would expand when hot, I pried the flywheel back until the crank was against the front thrust bearing surface. I then stopped prying and tightened the clamp. What I'm trying to figure out is exactly where the crank should be within the front/rear clearance (in the range of 0.110 to 0.712 mm) when tightening the clamp.
TIA
Don Burrows
87 S4, A/T, (Parked)
Factory Shop Manuals Volume III , Section 39, pages 137-143 has the procedure for Adjusting the Drive plate and states the following at the topof the page:
"To avoid axial pressure on crankshaft and crankshaft thrust bearings, the connections between flywheel and drive plate (distance X) MUST be checked and adjusted after replacement of engine, flywheel or central tube. This adjustment is not necessary after replacement of transmission or transmission parts"
***
Please note the parts differences for 85 and later referenced on pages 137-138 before proceeding.
As Jim and Mark stated earlier this is usually caused by incorrect repairs and is not necessarily a defect or a "weak spot" in your 928. This is just another reason to be sure of your mechanics abilities and/or your own familiarity with the proper procedures for repairing your 928 if you do the work yourself.
David Roberts
928 SPECIALISTS
As some of you may remember my drive shaft broke almost two years ago. I have also complained of a resonant vibration at around 3000 rpm which I have previously listed to seek opinions.
We posted a suggestion that it may be prudent to regularly check the tension of the flex plate to ensure that the thrust bearing is not overloaded. I took my S4 into the local dealers this afternoon and we carried out this check. When the pinch bolt was released the flex plate popped back by about 4 to 5mm! I shuddered when I saw this.
We also checked the crank end float which was approximately 0.5mm or on the outer limit of the tolerance range. Two years ago we checked this and it was half the amount. We are not entirely sure about the gauge that was used so we are going to recheck this in a day or two with another dial gauge.
After the adjustment was made a trial run indicated that the vibration at 3000 rpm had been significantly attenuated albeit there was still a little roughness. I will comment on this when I have done a bit more mileage.
What does all this mean?
First of all I am confident my drive shaft was replaced correctly two years ago. So, one of two possibilities has occurred, either the drive shaft has stretched or the splined central boss has moved forward. Whether or not there is damage to my crank thrust bearing remains to be seen but without doubt it has been under more load than it might otherwise have been and, subject to further checks, may well be at the back end of its theoretical service life.
Given the apparently unreasonable incidence of torque tube failures on S4 automatics and/or destruction of the main thrust bearing I am rapidly coming to the personal conclusion that for some reason our cars may be prone to some kind of design related failure. In Oman we have seen 4 torque tube failures in a vehicle population of around 30 machines in the last two years. Interestingly all of them were S4's or GTS's, none were earlier models [of which we have plenty here] and they typically had around 50 to
60k miles on the clock. I note that the recent Rennlist failures also had this type of mileage on them.
This begats the question why does it affect the automatics? Not sure on this one but I have a theory that it may relate to the way in which the gearbox is set up. The gearbox has a vacuum modulator. Set to one extreme the change is soft but sloppy. On the other extreme it is quick but a little thumpy. My gearbox has always been quick on shifting. Remember, even though the auto box is a Mercedes Benz design, the valve body was modified by Porsche to give a sportier performance. I am starting to wonder if sharks with their box modulated [intentionally or unintentionally] on the sporty side become more vulnerable to shaft failure because of the torque impulses exceeding the fatigue life criteria the machine was designed for. If this is the cause then it may be unfair to describe the failure as being "design related".
The torque tube, besides transmitting the power, also acts as a transmission shock absorber. The shaft continually winds up and under constant load twists proportionately to the torque applied [a simple application of Young's law]. Excessive shock loading [during gear changes for instance] may well have an impact on the fatigue life of the material.
Hence, if the shaft is exposed to more torque than it can absorb with the elastic limit of the material or if the torque cycles applied to it mean that the fatigue life is significantly reduced, one can reasonably predict that the torque tube will stretch and ultimately fail. As it stretches, it thrusts in a forward direction and la voila- the thrust bearing saga.
If you are lucky, the torque tube goes pop and if not the whole engine goes due to thrust bearing failure.
It only takes half an hour for the mechanic to carry out the check for the tension on the flex plate and about an hour if you want to check the end float on the crank while you are at it [recommended that you record this].
If you own an S4 or GTS automatic and you have not had this checked I strongly recommend that you consider doing this immediately and ask for the check to be built into your services. If there is a design weakness we cannot prevent the torque tube failure but we can protect the thrust bearing.
There are other reasons as to why the clamp may have moved on the splines. Incorrect torque being the obvious one, maybe vibration, but this would not explain the torque tube failures.
Regards,
Fred R
Oman
1990 S4 auto- questionable end float!
I would like to thank you for your post on what seems to be a growing concern that most of us were blissfully ignorant of just a short time ago. I cracked open the manuals on replacing the torque tube and saw the procedure for screwing down the clamp *after* bolting the six "drive plate attaching bolts." Undoing the clamp and retorquing seems to be a straight forward procedure that can be done by most at home. Am I right about this or will simply unscrewing the clamp, letting it adjust, then retorquing it not suffice as periodic preventive maintenance? This would seem better than just ripping open the oil filter to look for shavings. As far as the torque tube, how about softer settings for the gear changes? Just trying to find some proactive solutions to these concerns. Any of the enlightened want to share their thoughts?
Constantine
1989 928S4, Samtrot Metallic, AT (and nervous)
I've only driven a hundred miles or so after replacing my torque tube and am about to try the check that you did. You said that you saw that the flex plate popped "back" by about 4 to 5mm when the clamp bolt was loosened. When you say back do you mean that the hub of the flex plate moved toward the rear of the car when released, or that it moved toward the flywheel?
I have heard that torque converters, in general, tend to expand when they get up to operating temperature. This may explain why most of the reported failures are in automatics. This would make the failures occur at the rear thrust bearing surface due to the thermal expansion of the converter added to that of the driveshaft being greater than the increased expansion of the tube resulting from it's alloy construction, resulting in a net expansion of the shaft relative to the tube.
When I assembled my drivetrain I first confirmed that the shaft was riding free in the flex plate hub, then pried the flywheel to the rear of its play before tightening the clamp bolt. If the above amateur analysis is correct then I should be OK. I'll let you know what I find.
PS. Wouldn't it seem more logical that the torque converter, being a fluid coupling would absorb torque spikes to some extent and thus be easier on the driveshaft than the "hard" connection produced by the manual setup?
Don Burrows
87 S4, A/T
Here is the TSB from Porsche and outlines their theory... or should I say facts.
While it specifically about 89 and later autos, I feel it also applies to earlier twin coil engines that have an ignition coil (or wire) go bad.
++++
Broken Central Tube Shaft Vehicles With A/T
9228porsche01
July 7, 1992
Model 928 S4
Group 3
Part Identifier 3903
Number 9206
Subject: Broken Central Tube Shaft Vehicles with Automatic Transmission
ATTENTION: Service Manager/Service Technician
Models Affected: 928 S4 Model Year 1989 to 1991
Concern: Activation of the ignition monitoring system (injection circuit switched off fault codes 1131 or 1231) can lead to breakage of the central tube drive shaft.
General Information: Oscillations in the central tube system that occur when the ignition monitoring system has switched (flywheel effect) can lead to breakage of the central tube drive shaft. This can occur only in vehicles with automatic transmission where the vehicle is operated at an engine speed of approximately 1000 RPM. Possible causes are:
- Damaged or defective exhaust gas temperature sensors.
- Possible damage to the ignition coil wire left side (in driving direction) between the ignition coil and distributor cap.
- Poor grounding of the mounting plate for the ignition final stages.
- Poor physical connection of the electrical plugs on the ignition final stages.
Parts Information: A new version temperature sensor, central tube and coil wire are installed in production.
Temperature senso, Part Number 928 606 155 02
Central tube with changed material for drive shaft, Part Number 960 421 012 07
New coil wire with hose covering (for left side), Part Number 928 602 040 01
Repair Information:
1. If the central tube drive shaft is broken, replace the central tube with the new version part (see parts information). Refer to Technical Bulletin Group 3, Number 9203, dated May 5, 1992 for hints on central tube installation.
2. Replace the left side ignition coil wire with the part number listed in this bulletin. Be certain the coil wire is routed freely and not under tension.
3. Check all ignition components and connectors for corrosion, tightness, correct connection and damage. Repair or replace as necessary. If an ignition circuit has malfunctioned, an LED indication will be given by the ignition monitor relay located on the L-H control unit mounting plate.
Ignition circuit I (cyl. 1-7-6-4) Red diode
Ignition circuit II (cyl. 3-2-5-8) Green diode
4. Replace both temperature sensors located in the exhaust ports:
Model '89-'90, cyl. 4 and 8
Model '91 cyl. 3 and 7
Use the new version temperature sensors listed in this bulletin.
The function of the ignition circuits and light diodes located in the ignition monitor relay remains unchanged. It is not possible to determine from the LED display of the ignition monitor relay if one or both temperature sensors are defective or which temperature sensor has failed.
When installing temperature sensors, coat the sensor adapter threads with molykote paste HTP (white) and torque sensors to 10 N-m.
5. After the temperature sensors are installed, the voltage difference of the sensors must be checked in order to ensure proper operation of the ignition monitor system.
Checking sensor voltage difference:
- Start engine and bring to operating temperature.
- Loosen the mounting bolt for the ignition monitor relay and pivot the relay up to gain access to the plug terminals Do not disconnect the relay plug.
- Set volt meter to the millivolt range and connect leads between E1 and E2 of ignition monitor relay (Figure 3, white wires). A digital volt meter must be used. Polarity is not important.
- Measure voltage with the engine idling and again at approximately 2000 RPM. A maximum difference of +2.5 mV or -2.5 mV (depending on polarity) is permitted. If the voltage difference is above 2.5 mV, stop the engine, loosen and rotate one temperature sensor. Retighten sensor and check voltage difference. If the difference is above 2.5 mV, stop the engine and rotate the other sensor. If after rotating the sensors to different positions, the voltage difference is too high (above 2.5 mV) the temperature sensors are defective and must be replaced.
David Roberts
928 SPECIALISTS
When I finished installing the torque tube about three hundred miles ago, I pried the flywheel back from the engine, which was stone cold, until I heard the crank make contact with the thrust bearing, stopped prying and tightened the clamp bolt. Yesterday evening we put it on a lift while still at operating temp., fitted a dial indicating micrometer on the flex plate hub and released the clamp bolt whereupon the hub moved about 0.025" to the rear. We the checked the end play and found it to be 0.127 mm, well within the new bearing spec of 0.110-0.312 mm. We then pried the flywheel away from the engine to set the crank several thousandths off of the front TB and tightened the clamp bolt. We let it set all night and then found that the hub, still clamped, had moved to the rear about 0.005" and that's where we left it.
Don Burrows
87 S4, A/T
I have been assisting 3 friends with automatic transmissions in trying to determine if crankshaft thrust bearing wear is excessive on their cars. For simplicity, I have named the cars A,B and C. Here are the findings. "Hub movement" means: with a dial indicator on the center of the thrust plate hub, loosen the hub clamping screw and record movement of the hub. This shows the preload on the crankshaft. Presumably, no preload is desirable.
Car Year Mileage Hub movement CS End play
"A" '89 85K .120" .040" .009"
"B" '89 114K .100" .002"
"C" '88 44K .105" .016 .007"
We also checked the difference in preload caused by a cold car and a hot car using car "C". After making the initial check and finding .105" hub movement, we tightened the hub clamping bolt with no preload. The car was then driven ~2000 miles including one DE. We then checked the car cold and found .016" preload. Hub migration? We reclamped the hub and drove the car ~30 miles and rechecked the preload hot and found .003" preload. It appears that the shaft/torque tube do not change enough in length from cold to hot to affect the preload. Or was the .003" change caused by migration? Car A was also rechecked after 2,000 miles and the hub moved .040".
It also appears that the hub does migrate forward enough to put significant pressure on the thrust bearing, although the wear on cars A and C seems acceptable.
To try to stop migration on car "C", we used Loctite 290 penetrating formula on the hub splines and 242 on the threads of the clamping bolt, although the bolt does not appear to loosen. We will check eriodically to see if this stops migration.
On cars "A and "B" we used 271 on the threads. All bolts were replaced and torqued to 110% as per advise from Porsche.
One thing that we don't understand is: why does car "B" only have .002" crankshaft end play? On car "A"and "C" the crankshaft "clunks" back and forth when we pry them. Car "B" does not appear to move, but the dial indicator shows .002" movement. The specification is .00236" (.06mm) minimum. It is hard to believe that a car with over 114,000 miles has less than the minimum axial play.
Is this a symptom of the dreaded thrust bearing failure? Is there another way to check for thrust bearing failure without tearing the engine down? (Update: 12-05-00 an oil analysis on "B" showed no problems.)
Earl Gillstrom '88 5 speed (.007 CS end play) 99,000 miles
I have some possible good news for automatic owners that are worried about crankshaft thrust bearing failure. One of the cars that I have been monitoring for drive shaft movement in the front hub of the thrust plate has stopped moving. We did an experiment on Gary Knox's '88 automatic (car "C" in my previous email) that seems to have stopped the movement of the shaft. Here is what we did:
Removed the pinch (clamp) bolt in the front driveshaft hub. This relieved the thrust plate tension and allowed the shaft to attain the proper position.
Poured Loctite 290 (penetrating formula) into the three slots in the hub. The intent was to Loctite the shaft to the hub without disassembly. Disassembly requires removal of the torque tube. You should "prime" parts before assembly, but it is pretty time consuming to R&R the TT.
Installed a new bolt P/N 931.421.240.00. using Loctite 242 before assembly, torqued to 65 ft.lb. Porsche had recommended to Fred Rourke's mechanics, replacing the bolt and tightening to 110% of recommended torque. The standard torque is 59 ft.lb. The Loctite was our idea. I doubt that the Loctite on the bolt was necessary, but it can't hurt.
Let the car sit for 24 hours. Loctite says that a full cure takes 24 hours.
The car now has about 2000 miles on it since we did this, including two days of drivers education with NO hub movement. You can say that this is not a long term test, which is true. But we checked this car previously and found that the hub had moved .016 in about 2,000 miles and one DE. The first check we did, there was .105" movement (40,000 miles). So it is very encouraging. This is not an expensive procedure. About $6.00 for the bolt and $6.00 for the Loctite. It takes about an hour or two depending on experience. Check the crankshaft end play while you are in there. We painted the shaft splines white where they enter the clamping hub. After reassembly we could look through the hole in the bottom of the bell housing cover and see the painted splines. We think that we can do a quick spot check for shaft movement without any disassembly at every oil change by looking in the hole. Maybe a small diameter fiber optic light would make the job easier but the white paint helps a lot.
Car "D" was done on 11/11 using Loctite on the splines. Unfortunately we used red paint, so it may be harder to check hub movement without disassembly.
Car Year Mileage Hub movement CS End play
"D" '89 58K .134" .005" (added 12-05-00)
Here is the procedure:
Drop the exhaust at the manifolds.
Remove the bell housing bottom cover.
Install a dial indicator on the rear side of the forward Drive Shaft Hub.
Loosen The hub clamping screw and watch for hub movement.
On the three automatics that I have done this on, the hub moved back between .100"and .120". This preload puts pressure on the rear face of the crankshaft thrust bearing. If the hub does not move more than a few thousandths of an inch when you loosen the pinch bolt then all is OK. (Update 12-05-00,
Car "D" had .134" movement.)
After the pinch bolt is loose then put the dial indicator on the flywheel, (not the flexplate). Pry the flywheel back and forth to check the crankshaft end play. The spec for later engines is .0024" to .0076". Wear limit is .016".
If your end play is more than .016", then you are experiencing "Thrust Bearing Failure".
If you are installing a TT, clean the shaft and hub splines with Loctite primer before assembly. Tighten the forward hub pinch bolt last.
Pour Loctite 290 (penetrating formula) into the three slots in the hub. It doesn't matter if hot or cold or the position of the crankshaft.
Install a new bolt P/N 931.421.240.00. using Loctite 242 before assembly, torque to 65 ft.lb. The standard torque is 59 ft.lb. I doubt that the Loctite on the bolt is necessary, but it can't hurt.
Paint the shaft splines white where it enters the hub for future verification.
Reassemble cover and exhaust.
Let the car sit for 24 hours. Loctite says that a full cure takes 24 hours.
Look through the hole in the bottom of the bell housing every oil change to check for hub migration.
The pinch bolt is 10 mm with an 8 mm "Allen" head. Hardness is 12.9.
Part number is 931,421,240,00.
I will try to assemble a list of results if you try this experiment. Let me know how you make out.
Earl Gillstrom '88 5 speed (.007 CS end play) 99,000 miles
Thanks for the note. Initial checks on my S4 showed that the pinch bolt technique was working however I have booked a slot for tomorrow morning and we are going to re-check the situation. Painting the shaft is essential to easy monitoring and white is probably the best colour [we used gold because it was there]. Interesting the vibration period that I experienced at 3050 rpm has attenuated significantly since we the modification I advised you about. Before that, re-setting the bolt seemed to smooth things up but