Bigfoot928

More fuel. I still have the stub of the broken driveshaft

Bigfoot928

How many 928’s suffered a broken driveshaft and then tbf? My engine failure was due to ingesting sandblast media from an intake powder Coating job gone bad. The sand ate the rings and when the compression got low enough it wouldn’t run. Leakdown year was done and pulled the engine. On disassembly the thrust bearing had the nice welded beads on the rear facing surfaces.

Kiln_Red

I definitely agree with the suggestions to check crank end play on S3s. Maybe it is a non-issue for Euro S2s.. But, I have no doubt that I have personally observed notable thrust bearing wear on a US MY85. I can't recall the exact measurements but the car had 94k actual miles at time of inspection.

FredR

Sterling,

That is what I call a "classic torsional failure"- mine showed exactly the same signs and that failed after 84k km [50k miles] and about 8 years after delivery- not a mega mileage by any means but the car was reasonably used to say the least and not the kind of thing one would expect to experience. As you invariably would have seen on the shaft, there were longitudinal cracks that delaminated a few mm towards the centre of the shaft and at some point the residual material that still had structural integrity snapped due to excessive torsional loading relative to the amount of material left.

That you also had TBF is indeed a first of class observation from my personal point of view- I have often expressed my opinion that drive shaft failure, when it happens, is a pre-cursor to TBF if not corrected- kind of like a "safety valve" if you like and your case arguably proves the point albeit have no recollection of such example- remind me not to fly with you!

I also have a feeling that failure might also be a "Badge of honour" - i.e. it happens on examples that are driven as they were designed to be driven- that was the case with myself [at the time] and the previous owner- a Dutch chap! Days long since gone given the tools currently deployed by the local boys in blue [and quite rightly so].

GregBBRD

Very interesting!

That's definitely very different than the two I've had break. Mine were cracked and broken in the lengthwise plane. The cracks looked like the "Devil's Postpile" rock formation, in California. Sean has a picture of one, just like mine.

Paging Sean....

Your failure looks like it occurred right at the base of the splines...like there was a stress riser from the manufacturing process...perhaps a completely different type of failure.

skpyle

Christopher, listen to me: you are pissing in the wind. I mean no disrespect, but you are dancing around the issue, trying to avoid checking your 86.5 auto for flexplate migration. I OWN a 1986.5 auto that has had TWO documented cases of flexplate migration. When I bought her, the shop released the flexplate, something to the effect of 4mm preload. Crank endfloat was on the tight side of perfect. They replaced both the front and rear pinch bolts and torqued them to the updated spec of 66 ft/lbs. I drove the Red Witch for only 2000 miles before sending her over the WYAIT cliff. Amongst the work, I found the flexplate was preloaded AGAIN! The very slight metallic sheen in the drained engine oil told me the thrust bearing had been suffering. Crank endfloat is still good, but not near as perfect as it was.
Bottom line, get under your 928, release the preload, replace the pinch bolts, fit a secondary clamp, and have a wonderful time driving after that!

FredR

On the original GTS motor that was in my current 928 the crank thrust face lost metal and the thrust bearing face was about half the thickness of the stock item giving a residual end float of 1.3mm. At that point the crank webs and the crankcase then became the defacto thrust bearing and the oil gets laced with casing alloy not to mention everything else that gets machined off the crank and the thrust bearing. .

SeanR

Here ya go.

Christopher Zach

Hm.
Thanks Seth, your story reminded me why I was concerned about this: I remember reading your post on that and realized "Man, this guy had a fine car, they screwed with the bolts, did it properly, and 2k miles later it was eating the bearing".

I'll check to see if anything is loose and check the torque on the bolts, if there is no distortion on the flexplate I'm leaving it alone. What's a secondary clamp, I've seem reference to the super big clamps that look like they will never move, but does one have to drop the driveshaft in order to put one of those in?

ROG100

I have had an 86 here with TBF. In fact IIRC it was a car Heinrich bought a number of years back.

Geza

See post 31 Christopher

Christopher Zach

Oh that goes *around* the existing clamp? Man that's cute, no vibration/balance issues I assume?

Looks trivial to install otherwise. Hm.

FredR

Exactly the same type of failure as Sterling's and mine I would say.

The remains of the shaft tell a more complete story as in the photo in Constantine's post but one can still see the signs of the fragmented outer shards that initially crack longitudinally and then the residual central section left to take load ultimately gives way under shear to finish the failure off with a big bang and then leaving you to coast to a halt with the thing grinding away as the flex plate holds the splined section at engine speed [idle by then] and the shaft spins at road speed or whatever and the flexplate pre-load tries to push the stub into the shaft.

Mine failed in the middle of nowhere as I was overtaking some chap leaving me with the car by then going backwards relative to the car I was overtaking a split second earlier- quite surreal and that before mobile phones were available!.

GregBBRD

I agree. Not what I remembered.

I'll look for my picture.

Rob Edwards

Pic of Devil's postpile rock formation, just west of Mammoth Lakes, CA.