Randy V

This was posted by Martin Bishop over on the 928 SOCAL site.

I'm posting it here so it will be available in the archives - hope you don't mind Martin. Wish I knew about this one before I had my torque tube replaced earlier this year.

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Thanks to all for your help in debugging my transmission rattle. Especially thanks to Dr. Bob and Jim at Devek for convincing me to take it step by step prior to just replacing the torque tube, and for the trans service procedure (thanks again Dr. Bob)
I have been living with the trans rattle for over a year now, everyone I talk to says that it’s the torque tube. Although it is the torque tube, the procedure to fix is much simpler.

The rattle occurs during idle and is very obvious while you are under the car. It sounds as if something is bouncing around in a metal box, the noise is very obvious when you turn the car off, as it will continue while the exhaust no longer can be heard. When you shut it down, the noise can be heard for about 1 second and comes from the transmission area. I have heard people describe this as loose marbles in the transmission. Lucky Ekman even said he thought the sound might be ball bearings from the torque tube loose in the rear of the torque tube.
Now the fix. This took me all day because I went to buy fluids and a new torque wrench to ensure precision (my old one had been dropped many times… it was a cheap one)

I drained both the transmission and the differential, making sure to get everything out of the torque converter, and replaced the trans filter and gasket (was last done 20k ago). I replaced the fluids with Mobile 1 ATF, and Mobile 1 Gear oil.
I then took off the front bell housing, and loosened the TT (torque tube) pinch collar.
I took off the rubber stoppers on the rear TT site hole, and the TC (torque converter).

I then rotated the engine clockwise and tightened the TC flex plate bolts to 34ft lbs each. I held a flashlight near the TC site hole and watched until the head of the bolt was exactly where I wanted it then moved over and tightened it to spec.
Once I had all of the TC bolts tightened to spec, I tightened the rear pinch collar to 66ft lbs (110% of spec). This one was more tricky as I was unable to see in the site hole of the TT from where I was turning the engine.

Once I finished tightening the rear TT pinch collar, I moved to the front, and torqued the flywheel flex plate bolts to spec. Again, back to turning the engine. This time it was a piece of cake as I was turning right next to where I needed to look for the pinch collar.

I completely removed the pinch collar bolt to ensure I was taking any preload off the flywheel and even tried to move the flywheel aft. Once I had everything situated I torqued the front pinch collar to 66 ft lbs.

Once I got everything back together I started it up and the noise was completely gone! I am so relieved as I really did not want to have to put the effort and $$$$$ into replacing the torque tube.

This was a pretty basic job, it just takes time and precision. If you have a rattle coming from the transmission area, I highly recommend going over all of these bolts and torquing to spec (and 110% on the pinch collars).

-Martin Bishop-

Erik - Denmark

Randy,
Very interesting report - But tell me, how will you explain that this tightening of all the bolts in the TT system have taken away all the rattling noice?
I mean that cannot be the change of the oil and the filter, then it can only be that you had some lose bolts in the TT system - Do you think that was the case?
If yes I will gladly spend a day in the garage to do the same - But for me it sound like a dream - Please explain

Randy V

Hello Erik,

This procedure was completed and documented by Martin Bishop - I have not done it myself.

Perhaps Martin will stop by to give you his first-hand ideas.

Erik - Denmark

Hi Randy and Martin,
Yes, I hope to hear from you Martin - It all sound too easy and too cheap!
Is your car still silent?

Martin Bishop

sorry it took so long for me to jump in. I had to dig up my password.

Yes it is true, I saw an old email string from John Pirtle (I think) a while back and it was confirmed by Jim at Devek. Jim sat in the car and correctly identified (thanks for the confirmation) the rattle.

The fluid change had really nothing to do with the noise, but it made the shifts better. I think I had a gasket leak, and torquing those pan bolts to spec helped that part out.

I don't know how loose the pinch collar was when I started (I should have checked), but I loosened them both and then torqued them down to 66ftlbs after removing any preload on the flywheel.

The torque converter bolts were all at 34ftlbs but I gave them a nice "little" snug just for the piece of mind.

The car had the rattle at idle and was very noticeable once turned off. Now it is quite, and no rattle can be heard anywhere.

I hope to get it up in the air again soon with a stethoscope to be sure, but I could not hear anything underneath

Worked for me, and YMMV. But I am a believer!

check link for full original thread <a href="http://groups.msn.com/socal928/general.msnw?action=get_message&mview=0&ID_Message=2516&LastModified=467 5383435841952256" target="_blank">http://groups.msn.com/socal928/general.msnw?action=get_message&mview=0&ID_Message=2516&LastModified=467 5383435841952256</a>

Martin

Erik - Denmark

Martin,
Thank you for your write-up - I will check my TT according to your instruction.

PaulCarrera

Thanks for this write up it has saved me a lot of time. Also had the horrible rattle and it was really embarrassing driving the car. I tightened the 6 bolts holding the plate and got a couple of pounds out of them but it made no difference to the rattle. I then released the pinch bolt to relieve the pressure ( there wasn't any pressure and the plate was flat). The bolt was not that tight so I tightened to spec and started the engine and the rattle has gone and the car sounds fantastic. I wish every fix was this easy.

FredR

Paul,

What year model do you have- 87+? Presumably you are talking about the flex plate pinch bolt. If so trust you have read the threads about TBF and the sensible mitigations available to prevent this appalling phenomena that has taken out the motors in many automatic transmission equipped examples.

No need to be fearful of this if you take the correct measures as most on this list have but simply tightening the pinch bolt to 110% of rated torque does not stop the problem on its own - worse it gives an inappropriate sense of security in my opinion.

Feel free to ask any questions- just let's make sure you are not the next victim if you are new to 928 ownership- trust I am not misunderstanding anything here with respect to your issue. If the pinch bolt was loose logic suggests your flex plate should have been on the move- did you paint an index mark on the coupling/shaft before letting the tension go? Hard to spot the usual 3mm of movement if you did not.

Rgds

Fred

PaulCarrera

Hi Fred my car is a 84 S2 euro so I don't think it is as much of an issue with the earlier cars from what I have read.
I set up a dial indicator on the plate before releasing and there was no movement and the plate is flat to within .05mm using straight edge and feelers and the crank end play is all within spec. Yes I'm new to the 928 world having owned 911's since the 80's, but I'm enjoying sorting all the little bugs out, have just finished pulling apart and fixing the window switches this morning. But thanks Fred I will look at what preventative measures can be taken

FredR

Paul,

Indeed the problems seemed to start with the later models that had a different drive shaft- something most seem to think was a retrograde step given the subsequent trail of destroyed engine detrius.

Always helpful to post your model variant with any queries/observations

Best wishes

Fred

PaulCarrera

Thanks Fred I tried to find were to add the car listings at the foot of the post as others do but can't find out how, maybe once I get on a pc rather than my phone

mj1pate

I know this is an old thread. Regardless; I'm in the process of firming up my drive shaft and flex plate connections.

Aside from the drive shaft pinch bolt, which specific bolts at the flex plate were suggested to be retorqued?

There are bolts that secure the clamp to the flex plate and there are bolts that secure the flex plat to the fly wheel. Which of these did the process suggest retorqueing?

zekgb

Clamp to flywheel.

mj1pate

I've verified that the manual states to torque the flex plate (drive plate they call it) to the torque tube at 34 ft-lb. I cant find a reference for the torque value for flex plate to fly wheel. Anyone have a reference for that torque value?

mj1pate

Bump