Feargal Sharkey

Just before Christmas the car died on me all together while I was driving at about 50mph, the dash lit up as if it had stalled and I rolled to the side of the road. Tried to start it up again and it acted like it had a weak/flat battery.
Got breakdown guy to trailer it home, got a new battery installed the following day and after a few attempts it started.

Later discovered the car would start from cold without any problems or weird noises, and would drive but when the engine warmed up and it had to idle at traffic lights would stall and would not restart.

My 1990 S4 has just been diagnosed with thrust bearing failure
Not only had the thrust bearing moved inside the crank, but the front bearing had seized solid onto the crank - why ?

I bought the car two years ago and the car had 78,000 miles on the clock.
It had a full main dealer service history, but was hardly used in the end.

Since I owned the car it has been serviced regularly (at much expense) by a local independent specialist with 25+ year experience of Porsche cars, especially the 928. He assures me the flexplate was checked previously and showed no signs of preload.

P.s. Anyone got a good short block for sale ?

UKKid35

Sorry to hear of the failure.

Did you discuss flex plate pre-load with the independent before the failure?

I doubt it would have ever been checked by the OPC because, AFAIA it is not on any service schedule.

AO

Yep... flex plate pre-load is the culprit. Pre-load should be released once a year on autos. 5-speeds don't have a flex-plate like the auto's so there shouldn't be any accumulated pre-load.

Black Sea RD

Hello,

Very sorry to hear about this happening to you! I noticed that you have a whopping 4 posts on this forum which means you have not seen many previous posts about this very topic. For your benefit do a search for "TBF" and "thrust bearing failure" in this forum and read away. You will learn quite a bit and see gruesome pictures of what the insides of your engine look like.

Sincerely,
Constantine

Feargal Sharkey

Flex plate preload was not discussed before the failure, but I trust him and if he says it was checked I have no reason to doubt him.

UKKid35

The reason to doubt is that your engine has seized.

The really sad thing is that it only takes a couple of minutes to release preload (assuming the car is on a lift). How lazy do you have to be to skip that, unless you are simply ignorant of the problem, which you say you never discussed previously.

928worldwide

thats a shame. Sorry about your misfortune.

Black Sea RD

Hi Andrew,

Having any pre-load on one's front flex plate is not a good thing and releasing pressure "once a year" is not acceptable. Front flex plate pre-load usually returns within a few hundred miles.

As we can all see from the post above, TBF is unfortunately still a problem for 928 auto owners, no matter how much we have discussed this problem here on this forum.

Cheers,
Constantine

928worldwide

Forgive me for not reading them, I drive 5 speed mostly. What is the solution?

Feargal Sharkey

I haven't posted, but I do read a lot on here - mostly due to the fact that I'm a newbie and don't feel accomplished enough to comment.

Over the past few months I have read plenty of stuff about TBF, just a pity I hadn't read it sooner and done something about it. I have also read about your clamp, loctite and even guys who have welded the shaft !

My block damage is not as bad as the pictures of TBF I have seen on here - but I'm told it's bad enough to mean it is scrap.
It has about 2-3mm groove at thrust face of block.

AO

I understand that's your opinion and your vested interest, but I respectfully disagree. There are many people on this list that use the annual release method without any issues. Obviously only time will tell if this method is as statistically effective as the others (Constantine clamp, locktite, etc.) but the price is right.

I should append my previous post by saying that the the majority of people on this list that use the annual pre-load release method, tighten the stock clamp to 65 ftlbs (vs. the spec of 55 IIRC) as a means to mitigate the migration along the shaft.

Finally, this serves as another reason why you should have a 5-speed.

blown 87

Constantine's clamp is the answer.

Mrmerlin

dont forget if your checking the flex plate for the first time that the rear pinch bolt MUST also be checked. IE remove it , note the torque of the fastener, inspect the bolt for damage to the bolt shank, if its damaged then it should be replaced. If it is clean then add some blue loctite to it and install it with 66ft/lb.
Make sure to center the drive shaft in the rear coupler if the bolt was damaged, this can be done from the front in the bell hosing area just tighten the front clamp, and tap on it either way, to center the shaft.
Then after checking front clamp and checking freeplay of the crank then tighten the front bolt the same procedure as the rear bolt, spray some white paint on the drive shaft splines and rear of the front clamp, to mark it.

928worldwide

There are many areas of possible improvement that have been addressed with the 928. It's going to be great to see what the panamera coupe or whatever it's going to be called has stuffed inside to see how far the factory took their knowledge.

borland

Sorry to hear that. You should be able to find a used replacement engine very reasonably priced.

It's my belief that the torque tube bearings and torque converter bearings are only good for about 75K miles before driveline noise becomes excessive. Every car model has its flaws and this is one area that Porsche failed on in my opinion.

The locktite or clamp solutions have no effect on reducing driveline noise.

I replace these bearing and appreciate the driveline noise reduction. I also greased drive shaft splines on my 90' S4 upon re-assembly, so I'm not sold on locktite or clamp solutions on a car with a new set of drive line bearings.

I'll check the flex plate next time I either drop the cover, or rebuild the torque tube and replace the converter bearings every 75K miles, which ever comes first.