Garth from all my reading of this problem, and i have read everything that i could find, the problem comes from the TT exerting forward pressure. The tranny expert in NY suspects the converter expanding, the landsharkOZ site talks about some argument of the TT growing like pinocchios nose.

The bottom line in all arguments is that the TT is pressing forward. When did it change to the hub moving forward on its own? Just the centrifigal(spelling) force of the little clamping hub is causing the damage?

If so what about lock tite on the splines contacting the clamp or welding the damn thing?

 

tv

The converter expanding theory can be discarded because here is a bearing in the front of the converter that prevents any forwards pressure on to the driveshaft.

What happens is very simple - for reasons that have been the subject of much debate, the front clamp moves forwards over time relative to the drive shaft thus making the combined assmbly longer. The shaft is fixed longitudinally at the rear so the flexplate gets flexed pemanently forwards exerting force on the Thrust bearing, with the well know expensive results.

In victims case what has happened it would seem that after the tranny work the tranny was put back in but the clamp at the front was tightened before the tranny was tightened to the torque tube (tranny would have been a bit too far to the rear at this point. Front clamp was tightened then tranny to TT bolts tightened pushing the drive shaft forwards in the process ........kaboom.

 

TV, The TT proper is no more than a ~4" steel pipe flanged at both ends. Inside are 2 or 3 carrier bearings for the driven shaft: both are steel, and do not grow in length.
The prop shaft ( driven shaft) within the TT is a solid steel bar, splined at both ends with a locating groove in the rear splines to dimensionally fit the rear flex plate .... when properly installed. [ in Michaels case, I still suspect that this step was botched - as well.]
The prop shaft cannot grow in length: if anything, when in torsion/under engine torque, it will shorten ever so slightly. Even so, it restores to the machined dimension when the torque is released - if not, then the materials elastic limit has been exceeded and it becomes plastic = imminent failure. This is exactly the operating principle of a torsion bar front suspension, often used to eliminate coil springs.
It is the observed forward migration of the front flex plate hub along the splines of the prop shaft that cascades the pressure to the thrust bearing.
Earl Gillistrom (sp?) authored a loctite #290 procedure to secure this hub - and in an earlier post in this thread I referred to my use and success in doing this.

 

Hi All,

Thanks jon for the "holy grail". Yes I met Nick with the amethyst S4 only last week. He was kind enough to bring along a mate who had exactly the same problem that I have now. (The guy won, now it's my turn...)

Cut and Dry? I'm not too sure but then again I'm almost struggling in keeping up with the discussion..

Constantine (08/27) you hit it right there : they should've been Auto trans-refit-specific in their warnings/notes. We still want them to say that warning applies also to Trans refit (but I have yet to read bill's scans)

I can see the hazards of fitting the trans without checking the flex plate; I can follow your argument about fitting in the groove of the drive shaft, but don't you think that precise argument could fall flat? You say, because the clamp has to align with the grooves on the drive shaft and the tolerances are small, and could cause a forward movement on refit. But they are claiming that because those grooves need to match the coupling ( double clamp ) bolts and are fairly precise, they COULDN'T possibly move the shaft forward ( or else it wouldn't fit - granted the protrusions of the shafts are EXACTLY the same before and after) ! That's the PRECISE argument they told me and I heard with my owm ears.

What your discovery of 39-46 (1992) shows, jon, is the complicated nature of using the manual. To be a 928 expert you would have to "eat and sleep" 928. That's why only SOME of you guys are experts. Ok...most. Unfortunately, I can't say that about some bloody shops.


A few points need clarifying in my particular case :

1. The workshop did not remove the TT or at least they claimed the didn't. As discussed earlier (constantine 08/25, Garth 08/25) I will need to argue that this "last step" (tightening pinch bolts in flange coupling) is really an inferrence in Auto Transmission refit . Do I have a strong argument? In order to do this "last step" does one need to remove the TT or drive plate housing?


2. The workshop did not remove the Drive plate housing ( nor the pinch bolt)but have instead suggested that some other person(s) have incorrectly installed the engine and caused a preload before their (the workshop's) trans work.!

QUESTION: Some have told me it's impossible but is it really impossible to cause a huge preload ( say, 10mm) on engine refit? You'll have to be a bloody donkey but - impossible?

QUESTION : Garth has said it ( 08/23) - and others too - that flex plate damage is a telling point but the way I see it flex plate damage from pre-load is the same (or similar), whatever the cause, be it engine refit or trans / TT refit. In BOTH cases you still have the flex plate too far forward NO?


Yes, Bill I will have to get it from Jim Bailey but my Morehouse CD's will be a damn good start, when I receive it. Thanks Jim. Thanks for the scans, can't wait to read it.
It'll make the difference betw cut and dry and touch and go. But I shall not rest....

Michael

 

Michael,

That groove on the rear of the driveshaft is not a precise fit. With the bolt loose, there will be some play, certainly far more than the fraction of a millimeter that defines the correct location of the drive shaft relative to collar/plate/crankshaft. The design itself is not such that it can be used for precision positioning, and AFAIK no mention of using the groove to establish precise position is referenced in the WSM.

Your points needing clarification:

1) No, the TT does not need to come out for this. The lower bell housing(Drive plate housing?) does need to come off. The exhaust would probably have to be loosened for clearance.

2) This is baseless. If possible, get pix of your untouched front TT bolts, bellhousing bolts, exhaust bolts, motor mounts, etc. They are going to have a tough time proving that the engine was pulled.

Your questions:

1) Possible to create a huge preload -- of course. Without proof engine was refitted, this doesn't seem relevant.

2) Regardless of how disassembled, whether from one end or the other, it could be assembled so that the flexplate is too far forward. Note also that it is possible for flexplate to be too far forward if system was never disassembled.

Some of the real auto trans experts might know the answer to this, but is it possible that the torque converter was rebuilt and put back together with incorrect final dimensions such that the rear clamp itself was too far forward? [edit] looking at the WSMs more closely, what I should have asked is if the shaft on the TC could be too far forward, moving the rest of the assembly forward?[/edit]

 

Hi Michael,

Give Nick my regards when you next see him.

In response to your and Dave A's post post above I was going to edit my post in response to tv regarding sequence of reassembly however I figured it would confuse matters so I'll correct it below.

What i should have said was

In victims case what has happened, it would seem, that after the tranny work the tranny was put back in. The bolts between the rear of the TT and the tranny were put in loosely. The rear clamp was then tightened. Then the TT to Tranny bolts were tightened and torqued. Thus pushing the driveshaft forwards.

So having corrected myself where does that leave us. A further, but not exhaustive by any means, search through the manuals doesn't appear to suggest that one should even look at the front of the TT/drive shaft when reinstalling the transmission. Bugger! However the reinstalling transmission section does not even state how or when you should tighten the rear clamp bolt between Torque converter input shaft and the drive shaft - cue to refer to the Reinstalling central tube section ?

As a reasonably knowledgeable mechanic, a structural engineer by profession who has acted as an expert witness in a number of court cases (not automotive) , and someone with a reasonable knowledge of the Porsche 928, (but by no means as knowledgeable as a Porsche approved dealership should be) it should be blindingly apparent, even though it does not perhap explicitly say so, that if one is up to date with all the technical data sheets etc, there is a very real need to ensure that when reconnecting the driveshaft at either end you must ensure that when the very last bolt is tightened and the car returned to the customer the driveshaft should not be subject to any pretension or precompression.

So having said that - my opinion FWIW is that they should not have put the tranny back on without looseneing the clamp bolt at the front end drive shaft, and then retightening it as the last step. You probably can determine if they did look at it just by looking at the front cover plat bolts or even better if you have cats on the car have the mounting bolts removed recently.

Going back to the comments they made about the 10mm misalignment - Is this their observation on trying to reconnect the rear clamp before the trannsmission was fully bolted back on to the rear end of the Drive shaft ? If so this implies they should have read the manuals and Tech publications more carefully and realised that the last "adjustment" should have been at the forwards end of the driveshaft not the rear end.

I hope this make some sense. See if Nick has a Torque tube and drive shaft assembly with a rear clamp and if it is possible to get say 10mm fore and aft movement at the rear clamp. I can't help as my 928s are both 5sp.

 

Michael,
I am a professional engineer, I have acted as an expert witness, I have been engaged in arbitration, I have also been engaged in large insurane claims of an engineering nature and I have owned a 1990 928S4 for over five years. I have done all my own maintenance except for the initial timing belt and water pump renewal just after purchase. I have done my own timing belt renewal, checked the flex plate load up and I have done my own automatic automatic transmission repair, however, I have not done an engine removal, auto transmission removal or central tube removal. so I cannot be classified an expert on 928s, but as a professional engineer involved with crankshafts, diesel engines, drive shafts, axial alignment and thrust bearing I have what is considerable by soe as experience.

In my previous posts I have mentioned "good engineering practice", however, in the case of the representative/s of PCM who actually did the repair work, I don't know whether they are automative engineers or trade certificated motor mechanic/s. What ever they are they were possibly further trained by Porsche to undertake repair work on their vehicles and when work is done by Official Porsche Service Centres that Centre should give a warranty on the work they undertook which should cover any related flow on effect from this work. From your point of view, you acted in good faith, because you entrusted your car to their technical expertise to fix the problem and return the car in good working order and condition. It would appear that they have not forfilled their side of the contract.

As previously stated the engine, central tube, automatic transmission and transaxle are ONE singular bolted up "transmission of power" unit. Good engineering practice would suggest that if one item of this set up is removed then upon its replacement the whole system should be checked to ensure that it fits back in place correctly with all the tolerances and clearances as required by Porsche's automative engineers checked and adjusted. In your case, that no preload, either forward or aft, was applied to the engine and its thrust bearing. To suggest that is was not necessary to check the TOTAL system set up, I believe is a 'dereliction of duty' on the part of the mechanic/s and PCM.

Unfortunately no specific words can be found within the public released information from Porsche, that make this check of the setup a requirement with regards to the specific reinstallment of the autotransmisson, however, I believe that there is possibly internal written word regarding excessive axial load being imparted to the thurst bearing of the crankshaft, that can lead to the short motor being damaged beyond repair.

I think the way to take this forward is to force PCM to produce "Proof of Evidence" to back up what they are saying and there was no need to check whether the engine crankshaft had any thrust bearing load imparted from the reinstalled gear box as it was reinstalled as it came out.

Unfortunately I don't believe PMC will hand this information over to you at this juncture, so what can you do about it?

I believe that there is sufficient evidence within the 928 owners community world wide, not to mention owner/s in Melbourne who have experienced the failure or who know about the type of failure.

As previously stated I would suggest that you need a lawyer with engineering experience who can understand the technical aspects of the failure to persue your case and mount good technical arguments.

From my experience I think PCM will take you right up to the doors of the court room before they will offer a settlement, because I believe they would not want to have the fact known that they are fully aware of the axial load creep from the central tube drive shaft via the forward clamp migrating as well as incorrect set up can cause the crankshaft thrust bearing to fail in service.

I also believe that the load on the forward flex plate should be removed after any work, specifically on any removal or reinstallation of any item withing the drive chain unit.

What I'm implying here is if there is any internal literature relating to these facts then the only way to get it is via "Proof of Evidence". If this turns out to be the case then it implies that PCM knew and also their mechanics should have also known of this requirement and therefore should have checked there was no axial load imparted onto the crankshaft thrust bearing, as it could cause the thrust bearing to fail in service.

From you previous posts PCM have already set the ground rules, "Don't listen to all that CRAP out there etc etc", so you have to construct a very formidable case indeed, which can be backed up by knowledgable engineering experts, more specific automotive engineering experts. If it ever get down to "push follows shove", your expert/s must be able to prove the point good engineering expertise and good engineering practice, especially if they are willing to use terms like "any qualified persons would have known and good engineering practice dictates that the clearances should have been checked prior to the boxing up of the job to ensure that there was neutral load on the thrust bearing of the crankshaft" can be used.

The owner who you met in Melbourne, was his car's repair work done by PCM ,which caused the crankshaft bearing to fail?

If this is the case you need to ascertain whether he would be willing to allow your lawyer to use this information as a precedent in your case?

Well thats enough from me as it is quite late. Hope it helps.

Tails 1990 928 S4 Auto.

 

Hi and thanks tails, jon, dave, bill, garth, con, ALL.

Comprehend and appreciate the point we've been homing in on : do up the panhead screw of the clamping sleeve LAST. Unfortunately, in black and white
it refers to "Removing and Installing of central tube"

More to the point, and relevant to TT as well as trans r&r, is the requirement
of no pre-load on flex / crankshaft. I have asked, and you have repeatedly talked about this zero stess/pre-load but apart from 39-46 ( "to avoid placing the driver plate ...under strain.." and bulletin 3903 where else is this important SPECIFICALLY, WHERE IS THE CHANGE FROM ( 0.3 + 0.2 ) to 0.0 ??

Isn't it an umbrella requirement (and holy grail? ) if the WSM states :
" item 7 is now 0.0 +0.0 " and that the flex plate needs to be relaxed at all times?

Regards
Michael

jon yr stone grey shark looks exactly like the one I once was a proud owner of.

 

Michael,
Unfortunately the workshop manuals cover all models from 1978 through to 1995 and depending when the manuals were purchased they would only include the updates to that date. The WSMs that I'm using are the CDs from Jim Morehouse and I'm not sure when they were published and whether there are updated sections which I do not have.

I have done a search, page by page to try and find any reference to a 'cover all statement' regarding that the no load on the crank shaft thrust bearing is now required. The only referece I have is Technical Bulleting # 9203 dated May 5th 1992.

I would request that someone on the 928 Rennlist forum, who has the latest set of hard copy WSMs do a search to determing whether Porsche AG committed something to print other than the above mentioned Technical Bulletin.

A few points need to be made here.

Firstly the car owners in the USA are lucky in that it is a requirement, I believe, to make everything written available to owners of vehicles, such as WSM and Technical Bulletins, whereas in some other countries this is not a requirement. In this regard in one Technical Bulleting # 8710 there is an important Notice included on the bulletin which states:

"PCAN (Porsche Cars North America) Technical Bulletins are intended for the use by professional technicians, not a "Do-it-yourselfer". They are written to inform these technitions of conditions that may occur in some vehicles, or to provide information thta would assist in the proper service of a vehicle. Special tools may be required to perform certain operations identified in these bulletins. Use of tools and procedures other than those recommended in these bulletins may be detrimental to the safe operation of your vehicle. Properly trained technicians have the equipment. tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bylletin applies to your vehicle. or that your vehicle will have that condition. See your Porsche Dealer for information on whether your vehicle may benefit from the information. Part numbers listed in these bulletins are for reference only. Always check with your authorised Porsche dealer to verify correct part numbers. 1987 Porsche Cars North America Inc.

Secondly on page 39-139 of the WSM printed in August 1984 relating to the position of the central tube, and it states:
"Position of central shaft and rear flange shaft is important to guarantee proper function.
Position between the central shaft and rear tube must be A=2 plus or minus 0.05mm".

Thirdly on page 39-141 printed in August 1984 relating to Adjusting Drive Plate (flex plate), it states:
"To avoid axial pressure on crankshaft and crankshaft thrust bearings, the connection between flywheel and drive plate (diatance X) must be checked and adjusted after the replacement of engine, flywheel or central tube. This adjustment is not necessary after the replacement of transmission or transmission parts". This page refers to the provision of "preload" of 0.3 plus 0.2 mm on the drive plate.

There has been a significant time period between 1984 and the issuing of the Tech Bulletin 9203, during which time I would suggest there have been instances when the auto transmission have been reinstalled without checking the protusion of the drive shaft of 2 plus or minus 0.5mm. The could have been instances where there could have already been excessive preload already on the flex drive plate by the migration of the drive plate clamp and during a repair where some other adjustment or the reinstallation of the transmissionat at the after end has caused the drive shaft to be move further forward execting more pressure on the crankshaft and thrust bearing causing the failure of the thrust bearing.

The second point above could effectively give them a hook to hang there case on except for Tech Bulleting 9203 which i believe recognises the fact of the forward drive plate clamp migration in service.

Hope some other 928 owner finds your required statement.

Tails 1990 928 S4 Auto

 

Michael

I'ld go back to what I originally said and what Tails also said - both of us having being expert witnesses in court on Engineering matters.

Keep it simple.

Wether is says so in the manual or doesn't is largely irrelevant. No one can argue with the fact that the crank should not be pre-loaded in either direction. Basic engineering says that if you re-install the transmission and tighten up the TT to transmission bolts after you have tightened up the rear clamp bollt you WILL induce compression into the drive shaft. This is bad.

taking it beyond the simple stage there are sufficient warnings in the manual and in the later tech publications to imply that you shouldn't pre-compress the drive shaft (thus pushing the crank forwards) regardless of what you removed or replaced. It would be reasonable (what the court will be looking for) to assume that a Porsche approved workshop will be intimately familiar with both the manuals and the car, and those things which are in the manuals but perhaps which require a bit of insight.

We are talking that you entrusted your Porsche 928 to an approved Porsche workshop and not to Flybynight Acme Shadetree car repairs ltd.

Keep at it.

Jon

PS where did you see the pic of Rhondas Stone Grey GT?

 

Thanks Tails, Jon

Understand the need to have no pre-load. Afterall I learnt it the hard way didn't I? But I was confused as to where and when they changed the 0.3 to no load.


What d'ya think happened there? Do you think they tightened the double clamp before converter bell housing? I've been wondering - how easy is it to pull out the converter bell housing loose from the double clamp when removing trans?
Seeing that it hasn't been removed / touched for 15 years; Does it get stuck? Do you need to knock it? use a crow bar? Lever the clamp free ?
Or does it slip away gently.

Cheers
Michael

Nick sent me a photo of the grey shark with the GTS mirrors. its a real coincidence - color and mirrors exactly like mine. I'm not sure if it depressed me or made me angry...

 

Tails,
the WSM on the CD is, as far as I know, the latest version available. I'm not aware of any updates to the manuals that have been made since I purchased the hard copy used approx 3 yrs ago. The fact that it covers all years does confuse things somewhat since the TBF phenom appears to ONLY relate to S4 autos (haven't heard of any 85/86 failing but could be wrong). It appears the S4 's desing is the one that is susceptible.

Victim, best wishes in your fight....sounds like you're getting some very knowledgable advice.

Jim

 

Jim,
Thanks for the advice regarding the WSM are the latest, it is good to know.
Just had a LH ECU failure and the "brain" is currently with John of JDSPorsche for rebuild and testing.
John arranged for a spare LH ECU whilst mine is being repaired.
Did you receive the report on the Auto B2 Piston Repair?
Best regards,
Tails 1990 928S4 Auto.

 

While there has been talk of this, I refuted the speculation that the driveshaft lengthens under load in no uncertain terms. My statement is on the landsharkoz page on thrust bearing failures, so you are misrepresenting the site when you attribute the "TT growing" statement to it.

 

Thanks Jim. Everyone's been helpful and some of the comments are invaluable.
I checked the date I first posted; it's been two weeks but there's been so much info for a novice like myself that it feel like two months! Thanks again for the cd's What'll we do without you!

Thanks Dave for your comments on the nature of the gooves on the splines. That claim by the w'shop has worried me for a long time i.e. the claim that if the bolts (on the clamp) and grooves (on the splines) match then it must be in exactly the same position as they were before they were removed. And if it is in the same position then everything will be aligned as they were before. Therefore, no additional load than was there before. I can see a judge getting conned into believing this!!
I can see that bolting the trans back to the TT and aligning the grooves and clamp is a fiddly process and difficult (right?).
I can see that the process of aligning and clamping the double clamp can actually cause pre-load. Right?
Therefore the claim that the pre-load is the same if everything bolts up nicely is uneducated. (incompetent?)
I can see them arguing that one shouldn't even bother checking protrusion
( 2.00+.5 ) as long as the bolts match the grooves.
Regards ( and Have a great Birthday sharkskin )
Michael