Erik - Denmark

DoubleNutz,
What is a 'DONUT'?

I woud like, if you ones again explain how you placed the extra bearing without removing the trans-axel, and your experience after you did 'the fix'

Earl Gillstrom

Borland,

I give up. I am only a lowly wrench with 50 years of automotive experience. I have only seen this problem on every automatic that I have ever checked and heard from many other owners with this symptom.

Let me know what you find if you ever check your flexplate pressure.

Steve Cattaneo

Disconnect the front drive plate from the engine as per WSD, V 1 page 10-4 first make a reference mark to the flex plate, rev. the engine to where you feel the vibration, vibration engine related. No vibrations TT, rear flex plate or transmission torque converter out of balance. Reconnect the front plate.

Disconnect the rear drive plate from the torque converter; first make a reference mark to the converter and rev the motor, vibration bad tt bearings, bent shaft or bad rear flex plate and or bearings. No vibration torque converter out of balance.

If the vibration only happens under a load like driving then possibilities are torque tube bearings or axles (haft shaft)


Do Earls fix, you will sleep a lot better I did.

Erik - Denmark

Earl,
Don't give up we all need 'a lowly wrench's' 50 years experience!

I think Borland's point is important, he just changed the trans-shaft and he still have the 3000 RPM vibrations and the same did SAB

You said you have seen this problem on 'every automatic' - Have you also seen it on the older models (pre S4)?

I would gladly do the Loctice fix, if I know why it works, but not before, because that must be 'a hell' of a job to dismount it again!

This week-end I will go and test my car for this vibrations and try to find the reason - I have to be ready for the 928Euro 2003 Meeting in Germany next week

Erik - Denmark

I went for a test drive with the following conclusion:
- The 3000 Rpm vibration are only present in high gear and only during acceleration
- I.e. that speed and not RPM related
- The judgement is therefore, it must be the two rear joint shaft, I will try to change them left/right (Run the other direction)
- My high speed vibration is gone - I tried with 235 km/h (150 M/h) with and against a strong wind (This is cured with the new front spoiler)

Earl Gillstrom

Erik,

The "Loctite fix" was developed to stop front hub migration. After doing the fix on 10 cars (all S4 except 1 '86) (all 4 speed), some owners said that they noticed a reduction or elimination of the vibration at ~3000 rpm. I received Emails from dozens of owners that were happy that the hub migration stopped. No one has told me that Loctite did not stop hub migration. I have never heard of an earlier car with hub migration.

A few owners have had to remove the torque tube for various reasons after doing the "Loctite Fix" and reported "it takes a lot of heat to free the hub".

Erik - Denmark

Good morning Earl,
You are an early morning man! (Yes, correct, we can sleep when we are getting old)
1. I am happy for that answer - I.e. it must have something to do with the increased engine torque (and the driving style = Right food)
2. Yes I can imagine
3. have you ever seen a broken trans-shaft? If not look carefully at this picture, here specially on the long part you clearly see that the shaft is twisted 15-20 degree! http://boards.rennlist.com/upload/trans-shaft.JPG

Earl Gillstrom

Erik,

3. Someone a few years ago thought that twisting the shaft was what caused the front hub to migrate. Like the twisting would try to squize the hub forward. It's probably the best explanation that I have heard of. That would also make more sense, that the higher powered cars were more affected.

Sab

I would think that's a slim chance. That shaft would not stretch more then a couple of 1000's of an inch before actually breaking.

But in any case I wanted to confirm, my vibration is not really heavy. Most people driving in my car actually don't notice it.
What is everybodys expirience with this mystery vibration minimal, medium or heavy vibration?
cheers,
Sab.

Drewster67

Recently I had similar vibration. I went through the entire car until I realized my power steering pump pulley was almost falling off. A few turns of the wrench (PIA, because I left everything in place) and well la - no vibration.

WallyP

Sab said:
I would think that's a slim chance. That shaft would not stretch more then a couple of 1000's of an inch before actually breaking.


Many years ago, a drag racer wrote to the "Hot Rod Magazine" tech column asking when to replace his axles before they broke - he was in a race class that was required to use stock rear axles. The guys at the magazine told him to start with new axles, blue them and scribe a line from end to end. Check them periodically, and when they twisted 180 degrees - yes, a half a turn! - to replace them. Still think that the 928 driveshaft will break in a few thousanths?

BrianG

So, where should I look first for an apparent rear wheel out-of-balance type of vibration that comes on at around 80 mph.....grows to about 90 mph and smooths out at about 100 mph? At 90 mph (the worst speed) dropping the car into neutral has no immediate effect on the vibration, but the vibration reduces with decreasing speed, just as it does with the transmission engaged.

New Michelin Pilot Sport tires were placed today, Road-force balanced and then spin-balanced on the car to +/- 1/4 oz. This made NO difference in the vibration.

Erik - Denmark

This afternoon I went to my sponsors' workshop (Garage) for doing a service check before I go to Germany for the 928EURO meeting.
When finished the work, and start lowering the lift, I heard Earls voice:
' Erik better check the flexplate' - I did and - uhps! - The flexplate was under pressure (I messured with a ruler on the flexplate ) it was concave!
I loosen the spline-clutch and 'wups' it moves app. 2 mm backwards and the flexplate became strait.
I know FOR SURE that here was a negative pressure (according to Shop manual page 39-51) 50,000 Km ago (8,000 Miles)
That strange, what is going on here? It is a 1984 S2 - 160,000 Km and also a pre S4 model - All 928 owners, listen to Earl and check your flexplate!
The next was the the result of my test drive: The 3000 RPM vibration has gone, or at least it is reduced - I have to do more test!
But what happen?
I can see two possibilities:
1. DoubleNutz therory - The front trans bearing move backwards, the the shaft is not proper supported - the vibrations move the shaft backward in the spline clutch (when the shaft bend-out) and get fixed here, i.e get longer - FOR THIS, EARLS LOCTITE FIX WILL HELP!
2. The balloing theory in combination with weard out converter bearings - Then the whole shaft will move forwards, but that will stop when the converter shaft bearings comes to the end of longitudinal play.

I am confused, so please help with good logic ideas!


For sure I wil check my flex-plate regularly in the future!

DoubleNutz

Erik, sorry I have not had much opportunity the past fews days to contribute here (things piling up on the "honey do" list). Please allow me to add this- The Loctite fix is a great preventative measure solution. However, if the TTB has already begun its journey of walking down the tube much of the vibration will come from the shaft itself whipping in the tube. A "less simple" way of observing this violent whipping action is to actually have completely removed a torque tube where the bearing either walked back a considerable distance or disintigrated in the tube- by hand- spin the shaft as fast as you possiblly can and watch the whipping motion begin as it slows down. It's a fairly violent whipping and will give the torque tube a good shake.

My point is- that the flex plate issue is likely only part of fiving the vibration problem, which is further exacerbated by the shaft itself whipping in rotation within the tube. I guess that means the entire problem cannot be fixed unless both issues are addressed.

Erik - Denmark

Pat,
Your statement makes sense
I still do not understand how you installed the extra bearing without removing the whole trans unit!
Do you did it yourself or you have only been told?