mj1pate

Never mind. Found it. Greg to the rescue:
https://rennlist.com/forums/928-forum/740334-torque-spec-for-flex-plate-bolts.html

marine928

My rattle was due to the rivets that Porsche decided to try on some of the 87 S-4's. I had to drop everything and drill out the rivets and replace with the original bolt setup. Real PITA. Also rebuilt TT with Constantine's set up and replaced clamps with Porkens. Naturally filter and fluids were done at the same time.
Minor adjustment to the shift cable and vacuum line resulted in butter smooth shifting and absolute rattle/vibration free ride. Like every repair, the results are worth the effort/expense when done correctly and thoroughly with plenty of WYAIT.

obie620

This worked a treat on my 83S 3 speed. Rear torque tube coupling bolts were loose. Re torqued all bolts to spec front and rear, the noise has now gone.

Randy V

Welcome and nice first post.

Ain't that search function thing magical?

Adk46

I just noticed the word "rattle" in the title of this thread. I've been scratching my head about a rattle that appeared suddenly after the winter lay-up.

It's from somewhere near the rear of the engine - I can't tell where exactly, even with a stethoscope. It does not vary in intensity or frequency with changes in throttle position, engine speed or car speed. This has made me think it was something static, like a loose bit of sheet metal or exhaust.

I last checked the pinch bolt about a year ago. I have a spare front exhaust section that I'll try soon - I'm imaging the ceramic bouncing around loose inside. I'll check the flex plate at the same time.

My big question is whether the rattles being described here are affected by engine speed. Seems they would be, but mine isn't.

Big Dave

Thanks for bumping this. Seems I have exactly the same symptoms as Martin did: only heard @ idle (goes away under load) and most noticeable when turning the car off.

Hoping it's this easy. Now I just need to find the time to do it. I rarely drive the 928 because of the noise. It turns heads for the wrong reasons!

NC928S4

I decided to tackle my "rattle" solo on one of the Hottest F days of the year. My rattle sounded more like a geiger counter and only occurred when not under load and when turning engine off. I couldn't take it anymore so I decided to go in. I followed the procedure outlined here verbatim.

The front flex plate was definitely bowed towards engine. I was surprised about this because I have a PKlamp in addition to stock pinch collar and this was relaxed just 2 years ago. When I released the rear pinch bolt the I heard the from plate relax. Visually, it did look noticeably flatter. I did notice a rub/chatter mark where the flex plate was rubbing on the fly wheel. Even before I relaxed the rear pinch collar the flex plate was not touching the fly wheel.

The migration of the drive shaft into the front flex plate is alarming. I know TBF has been discussed ad nauseam but it appears to me that thermal expansion of the shaft is occurring. The end of the shaft nearest the engine heats up the most so that end expands. The rear pinch bolt must be a stronger clamp than the front so the thermal expansion grows into the flex plate. Note that thermal expansion cannot be stopped and that stress from grow goes right into the front flex plate. If it grows or ratchets up over time you get TBF. Anyways that's my take. A possible fix for this would be to loosen up the rear pinch collar as a stress relaxer path.

I torqued all bolts as described. One of the TC flex bolts did shear of so I'm now driving around with 5 of 6 bolts. I will fight that battle another day.

The rattle is now markedly reduced but still can be heard when turning the engine off. I will likely get a new flex plate next time I go in, in the hope to completely remove the noise. This job is a bitch to do solo crawling back and forth to rotate the engine to get to each bolt.

dzaprev

I will try this weekend on my 80 928 , I have the same noise .