Re: Center Diff locking problems in 87 4KCSQ

[paul.heneghan@bbc.co.uk (Heneghan,Paul)]

From: rob_duvalle@co.washington.or.us

>It <the front diff lock> will engage _most_ of the 
>time at different speeds but when it does it makes a loud "thwang" and 
 you can 
>feel it shake the car.  

Check things like tyre diameters (the sum of the two at the front must 
 be the same as the sum of the two at the back), or more likely, worn 
 diff mounting bushings.

>Disengaging it can only be done by completely 
>stopping the car and going into reverse and coast a 
>bit backwards.  Others I have spoken with seem to think it is internal in the 
>diff from possibly years of non-use and rust.  Any other ideas.....?

I had this problem on my 1984 80q (same car).  I could only disengage 
 by dropping into second gear at 50mph, letting out the clutch and 
 taking my foot off the accelerator.  It was usually easier (read less 
 dramatic) to stop the car, put it into reverse and drive backwards a 
 few meters.

When I replaced the rear diff mounting bushes, this problem went away.  
 The actuator for the centre diff is actually on the rear diff, and a 
 long bowden cable actuates the lever on the centre diff.  If the rear 
 diff has shot mountings, it puts strain on the cable, preventing it 
 from disengaging.  If you drive in second gear and jab the accelerator 
 up and down, do you get loud bangs from the rear suspension - that's a 
 sure sign of rear diff mountings.  They are VERY easy to replace.

If all else fails, put the car up on ramps/stands and get somebody to 
 operate the diff lock and check the lights.  You can be under the car 
 looking at the actuators/levers.  Remember it only operates when the 
 internal locking sleeve is syncronized.  You may need to rotate a road 
 wheel to help it.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1983 Audi 100 Avant