Everyone..
Looking for help...I have an 86 928s with 75k that is developing a vibration when under acceleration. The problem only seems to appear for a second or two when the car has been coasting then under power. Problem starts about 1300 rpm and goes away by 1700 rpm. Engine mounts were replaced 2000mi ago. Any wisdom would be appreciated.
Thanks

 

NO DOUBT ABOUT IT! It's your TORQUE TUBE dude.

 

I would be thinking the dreaded TT as well given your recent MM replacement.

BTW - Have you checked to see if the MM are still okay? A quick look under the car would confirm this.

 

SOme where i remember reading that the later cars had 3 bearing tubes vs the 2 bearing tubes in the older cars.

SOmebody will correct me if im wrong.

 

I've done a bit of research in this area.

This is what I've been able to glean thus far......

Autos - came with 2 bearings/housings

Manuals - came with 3 bearings/housings

The original bearings where manufactured by a Germany company named '***', and are typically sized SKU 6006 (Auto) or 6007 (Manuals).

The bearings are classified as C5 - which is a high temperature rated shielded bearing. The C5 bearing is not currently available to the average consumer (you will find C3 bearings at your local parts store - with an average cost of ~$20 each). From what I've been able to find - a company in Germany named 'INA' sells a bearing product 6006 with a designation of 'RS'. This seems to be the best candidate for the replacement bearings.

Removing the the bearings from the TT and installing them is not as difficult as it might seem...actually pretty easy. I can provide more info if someone is interested in this area (ie Tshirt owner).

Lastly, looking in the Shop Manuals - one will find a statement in at least 2 areas that I now of now -

'The Drive Tube is not a servicable item and individual parts are not currently available'.

Hmmm....makes one wonder doesn't it???

HTH-

 

Thanks to all. My 86 is an automatic. If anyone has the method to quickly confirm the Motor Mounts condition please let me know. If it is indeed the TT, where do I get the replacement TT or bearings. Has anyone out there been through this?

Thanks again for the help!
Kdgrimshaw

 

6007 is in automatics. That's what I found in my untouched tube today. Also, that's what Errka indicated here:
https://rennlist.com/forums/4347082-post5.html

 

this one came back from the past 11 years old, still good to update so others may learn from the latest info

 

Lol...I was going to reply...lol...INA bearing has a huge plant near me...been in it several times....

 

When I searched for TT bearing info today, this was one of few threads that showed up, so I though I'd add my observation and Errka's. I ordered a bearing kit a long time ago, specifiying automatic 28mm shaft. Today I grabbed the kit off the shelf to discover the bushings are 25mm and the bearings are 6006.

 

Quick reference on stock configurations:

All 928 5 -speeds - Three bearing units, 25mm drive shaft, 6006 2Z C5

928 Autos up to 1986.5 - Three bearing units, 25mm drive shaft, 6006 2Z C5

928 Autos 1987 and up - Two bearing units, 28mm drive shaft, 6007 2Z C5

Special note 1: TTs could have been changed in a car's history and automatic 928s should be checked to confirm what size drive shaft is actually in the TT.

Special note 2: TTs could have been rebuilt in a car's history and have more or less bearing units in it and have different type bearings.

C5 is a very loose clearance fit between ball bearings and races, very hard to find.

 

Three bearings in a 86 auto for sure. No big deal to change once the tt is of the car. I had mine done in less then a hour using Constantine super bearings. The only way to go in my opinion.