gazfish

Hi All,

I swapped out my vacuum modulator over the weekend and while adjusting the pressure with the engine running I could hear a rattle from around the torque converter area.
A bit of searching pointed to loose rivets on the drive plate which has a service bulletin to replace with bolts. This size of project is beyond me and my driveway so I’ll plan to bring it to a qualified shop in the UK to get this done along with the usual list when the torque tube is out. It won’t be until the Summer though so is it ok to drive? If they are just loose could they rip off completely and leave me stranded or do more damage?

I ordered a cheap borescope and will try to see if I can get it in there to confirm signs of wear around the rivets in the meantime.

Thanks,
Gary

GregBBRD

Any streaks of rust, coming from the rivets, means they are loose.
Very common.
Truthfully, the bolt repair is about as poor a solution as a company could come up with.
It's a"patch", at best.
First of all, the bolts can not provide enough clamping pressure to keep the three pieces from moving.
And the bolts are so short, they are completely threaded, which means only the threads are keeping the pieces from moving back and forth against each other. The bolts wear out even quicker than the rivets did!
Shoulder bolts work much, much better, although the repair takes much longer and requires very precise drilling and reaming of the existing holes.
That's how I've been fixing this problem, for years.

gazfish

Thanks Greg, sounds like the next size up rivets might be a better solution if they can last 30 ish years.
Is there any reason the parts couldn’t be welded together, might be a stupid suggestion having not seen the parts myself.

GregBBRD

Welding on the flex plates would probably crack them, which is why they are riveted, in the first place.

Yes, the next size rivet would be a good solution.
Finding 8 of those and someone who has the tooling them would be the issue.
Maybe aerospace people?

Might be cheaper to buy a new one or find a used late model flex plate, where the problem had already been solved.
Try Mark Anderson at 928 International. Amazing people.

Chalkboss

Had this issue on my 87, sent the flexplate to Greg and had him fix it. No more worries, been probably six years since then. My rattle was loud, and the "rust witness marks" around the rivets prior to repair were negligible to me. I do pretty much all the work on my 928 but this is one area I just didn't want to tackle on my own.

GregBBRD

Gazfish:

I could easily package up the parts I use to do this repair and send them to you, with instructions.
The tools are pretty simple....a drill and a reamer. Not sure how expensive those are, but since the are generic American sizes, I don't think that they will cost too much.....I can check.
Do you have access to a drill press?

gazfish

Thanks for the offer Greg, really appreciate it. My problem is getting to the drive plate. Getting the torque tube out of the car on my gravel driveway is a bit beyond my comfort zone, there's a few 928 specialists in the UK that I'm considering. Don't like paying other people for something I can do myself, but I also know my limits.

GregBBRD

I understand that.
They did not make getting the flexplate out very user friendly.
When you get around to this job, we can reconnect, if I can be of service. (A shop may have the drill and the reamer...you may only need the hardware.)

gazfish

Don’t know if these photos indicate anything Greg/Anyone? The rivets looks rusty and not sure if that’s rust being thrown out from the centre or transmission fluid.

Constantine

Yes, the photos show excessive rust of the riveted area and your symptoms match.

The rattle usually goes away with the application of the throttle then comes back when idling. Classic failure.

Here is the Porsche TSB for this failure.

Follow Greg's advice for the fix. Also there are other WYITs to consider, like the primary pump seal R&R.

C531XHO

...what MY for the better design you mention Greg?