OBehave

A question for those that have actually experienced Thrust Bearing Failure,When driving or at a stand still,would an engine with a bad or going bad thrust bearing make any specific noises or vibrations ie: clunks,thuds, screeeches?How did you know to further investigate that perticular problem?I know the proper way to check is done during the PPI but I'm looking for something that would say "hey better check this out now" or "run as fast as you can".Thanks Ed

Mongo

Previous threads on here have said that there are really no known associated noises. The motor will stall at idle when operating temperature is achieved. Attempting to restart results in slow cranking. This indicates the crank is completely pressed on the rear thrust bearing surface (if the bearing is still there) while machining the engine block itself. A more extreme symptom would be if you are driving and the car's engine seizes up. Nevertheless, TBF is the nightmare of the majority of automatic 928 owners here (myself included). Check and release that pinch color bolt once a year or every 6 months.

James Bailey

Nope no noise at all....it just starts to crank slower on the starter motor when hot, starts to die at idle at stop lights , gets where it will not crank at all when hot. Let it cool down and they will crank and run O K for a while.l Often mimics a bad idle stabilzer valve or defective starter in the early stages.

OBehave

Thanks Andy and Jim for your responces. So theoretically speaking,if I do some small snaps of the throttle in park od neutral to say 3500 rpm and back and hear a clunk at the top of that rpm range and a nother clunk when letting off quickly,I can pretty miuch rule out TBF? Also how does the thrust bearing affect oil pressure if at all? Thanks, it's difficult to do a search with specific questions. Ed

James Bailey

Since the crank oil holes feed onto the regular main bearing surface and not onto the thrust bearing shoulders you have good oil pressure long after the block has been "machined"....

AO

If you are "theoretically" experiencing a clunk during those throttle snaps, I'd suspect motor mounts first before TBF.

Mongo

You can always change your oil right now and see if there is metal sticking to your magnetic drain plug. I did mine out of worry due to my idle issues and had no metal shavings or shards sticking to my drain plug magnet.

OBehave

Even at a stand still in neutral not moving do you think a thud or clunk could be MM's?

blown 87

Theoretically speaking, you could check your crankshaft end play and know exactly if it is TBF or not.

Just saying.

AO

Yes. If you're not moving and in neutral I think it is even more likely that it is the MMs. If it's in neutral (I assume it's an auto) there should be little to no torque applied to the trans mounts and certainly none to the half-shafts.

Other possibliites could include torque converter, rear flex plate, primary pump, and torque tube bearings. But, I'd put a digital camera under the engine and put it on movie mode and see what it records.

My guess is the engine is rotating with torque and upon settling, becasue the MM are dead it's hitting the cross members.

FredR

The chaps have nailed this one. The only sign I noticed when I purchased my GTS from the poor SOB who previously owned the car was the engine was rough as hell but no obvious mechanical noise. I knew from the history what the problem was and five minutes under the car to measure crank end float confirmed the GTS engine was wrecked.

I was in a good negotiating position as I has the only spare 928 engine in the country and probably the Middle East [recovered from my late S4]. I could easily have screwed the poor chap harder but I am not the osr twho can kick a chap in the nuts when is down and out so gave him a fair offer. When he hesitated I promptly told him my price would drop by $1k per day of deliberation- he accepted immediately.

I agree with Andrew, it sounds as though you need some new motor mounts. Forget about those dry bollack jack OEM things and go for solid rubber mounts from one of our regular 928 vendors. I believe you can get them really cheap these days if you know where to go for them.

Regards

Fred