tda1

Ok..So my car has a rattle that I had first thought was from the exhaust but now I've narrowed it to the torque tube. The rattle is only there when the engine is cold. Once it gets warmed up, the noise goes away.
My question is this....Is this a dire emergency and am I risking catastrophic failure if I continue to drive it. Other than that...the car runs great.
thanks.

Mrmerlin

it will be fine to drive it from the street to the garage to remove the TT

Tony

There is a lot of stuff under there that can rattle. Double check the heat shields....since you say it quits when the engine warms up its sounds "heat" related.
the TT doesn't really "warm" up...removing it is a big job so be certain what you have before you go taking stuff apart.

auzivision

How do you define catastrophic? Could it leave you stranded, yes. Could it self destruct, yes. Will the repair cost before self destruction be significantly less than after, maybe yes... maybe no... defends on what ultimately fails and potential collateral damage. To me there are only two catastrophic failure modes on a 928 and they both happened to be called TBF. Everything else is repairable and probably going to need addressing sooner or later.

Not only is you car the same and and color as mine... it seems to be exhibiting a lot of the same symptoms. I've had the cold TT rattle for a few years and many thousand miles... some of them fairly "spirited" too and nothing has blown. However, I'm fully expecting to do a tranny/TC/TT drop sooner or later... hopefully maybe this winter.

Bill Ball

ASSUMING it is the TT bearings, as you suspect, I've not heard of any catastrophic failures. They slowly get louder and louder over time and many miles and the TT starts to vibrate annoyingly. That said, a "rattle" is not the way TT bearing wear usually presents. They growl roughly and the sound is tied directly to engine RPM, at least with an automatic. With a stick shift you can isolate the sound with the clutch. Regardless, sure, your rattle could be a sign the bearings are loose.

One relatively easy thing to do is to pull the lower bellhousing cover and probe down inside the TT with a straightened coat hanger. You should run into the front bearing carrier at 10-12 inches in. I've seen them migrate to the center, 2+ feet in. When that happens, the shaft is not supported as it should be at the front, and the result is noise and/or vibration. Also, you can probe the rear carrier from an inspection hole (for access to the rear TT clamp), although you may have to drop the exhaust to get to it. Do the same coat hanger probe. THERE WAS A SITUATION LIKE YOURS RECENTLY WHERE THE BEARING CARRIER WAS FOUND LOOSE AND MIGRATED TO THE REAR.

https://rennlist.com/forums/928-foru...ery-sound.html


If your S4 is an automatic, there are other things to check WYAIT such as the front flexplate for bowing and the crank endplay and the front and rear TT shaft clamp bolts for proper torque. If you have not done this on this car, you DEFINITELY should now or very soon.

Here's my crank endplay guide:
https://rennlist.com/forums/928-foru...pictorial.html

If your S4 is an automatic, there a chance it is the rear flexplate (rivets vs. bolts). See attachment below. Through 1987 Porsche used rivets to hold the rear flexplate to the center hub that clamps to the TT. The rivets can get loose and rattle. The rivets cannot be examined directly unless the TT and torque converter (TC) cover are removed. You MIGHT be able to evaluate this by exposing the flexplate (accessible through the cover) and seeing it you can reproduce the rattle by hitting it. At the very least make sure the 6 outer flexplate bolts are torqued properly to the TC. One of those MIGHT be loose and rattling.

Exhaust leaks can sound deceptively like other things (primarily like lifter ticking) and definitely change as the car warms up. Perhaps there is something in or around the exhaust that is loose. Have you pounded on the exhaust system when cold?

Give us whatever other clues you have about how it sounds related to engine speed and where it seems to be coming from. Pinpointing noise source in the drivetrain is complicated by resonances and amplification along the entire length of the TT and in the TC cover and bellhousing.

jeff spahn

My car has the exact same symptoms. Rattles when it is cold, goes away when it is warm. My cause of this rattle is the TT. The rear bearing has gone kaput and part of it has migrated down the driveshaft and rattles against the rear pinch clamp.

I am having a new Constantine TT put in (with the 25mm race shaft and Super Bearings) on the 10th or 11th of October by Sean and I (depending on how drunk we are on the 10th).

I chased this for a long time. First thought it was heat shields, then thought it was rivets on flexplate, then wondered if it was the Torque Converter bearings.

Finally found it when I had the car on a lift during supercharger install. Pulled off rear pinch bolt cover in TT and stuck my finger up there. Lo and behold, a part of the rear TT bearing was sliding up and down the TT.

Is my TT noisey, not really. Just a very slight growl on the highway. Does the rattle drive me nuts, damn straight it does!

After this, I will have had every mechanical system off my car either by me or Greg Brown. Looking forward to getting this done!

Pull the inspection plug on your TT and stick your finger in there towards the front of the car. See if you can feel anything sliding around on the driveshaft. If you can, call Constantine and order a new TT with Super Bearings.

tda1

Thanks for all the info guys. The 'rattle' is not associated with the engine revs and seems to stop very shortly after it warms up. Then I don't hear it again unless the car sits for a while. I'll be doing alot of checking post frenzy I'm afraid.
this journey never ends
I do love the car though...

MFranke

Is the rattle dependent on speed?

If so, check the heat shields again for clearances. Check the clearance from the shields to the belly pan hanger mounts.

Also, flex the shields with your hands and listen to them.

John Pirtle

http://members.rennlist.com/pirtle/ztrans_marbles.txt

Check this link. I had a similar problem years ago and it was the shaft bolts were loose. I tightened them and no issues since, about 120,000 miles later.

I hope it's that simple for you.

John Pirtle
87 a/t 252k

auzivision

Holy old thread resurrection Batman! From a legendary source to boot... I believe this is from the days before Rennlist.

Anyhow, I'm hoping maybe this is what causing my my random rattle... that would be too easy.

Big Dave

Hmm...I have a rattle on my '85AT, and I had assumed it was the TT. But the rattle goes away under load. It's only loud at idle or when my foot is off the gas. I don't drive the car much (because it's embarrassing to have that rattle) so I've not spent much time chasing down the source. I did check the bell housing and flex plate...all tight. I haven't checked anything in the back or heat shields.