HELP!!! Rear Diff Problem?

[Fred Munro]

Hi Jason;

If your diff won't unlock, it is usually because the lock lever mechanism on
the diff is corroded. The vacuum system can pull the lever to lock the diff,
but the return spring isn't strong enough to unlock the diff. Get under the
car and manually move the lever into the "unlocked" position. Free up the
mechanism while you are under there.
The light goes out at 40 kph because the system is designed to automatically
unlock the diff at that speed. If the lock lever is stuck, the light may go
out (indicating the signal is sent to unlock the diff) but the diff may stay
locked.
If you are driving at 140 kph with a locked rear diff you will ruin the
diff. The car is also unstable because, as you have noted, turning with a
locked rear diff causes one or both wheels to skid around the turn - the
wheels want to rotate at different speeds as you turn but the locked rear
diff keeps them rotating at the same speed. This is why your car feels
"nasty" when you turn.
Get the diff unlocked before you drive the car. The clicking noise may be
due to diff damage - there's a lot of stress on a locked diff when turning
at high speed.

Good luck!

Fred Munro
'94 S4  122k km

----- Original Message -----
From: "Jason Stone" <jason_r_stone at yahoo.com>
To: "Audi List" <quattro at audifans.com>
Sent: Monday, January 22, 2001 4:19 AM
Subject: HELP!!! Rear Diff Problem?


>
> I've tried to include as much info as possible - I
> will answer any questions to help me know where to
> first look...
>
> Help!
>
> Problem:
> ========
> Loud clicking noise coming from rear of car - pretty
> sure it's the rear diff - it does go away but left
> turns always bring it back.  Something loose in the
> diff?  The other thing - the rear diff is now locked
> and the ABS is off - the switch to unlock the centre
> diff does not unlock the rear diff - the switch is
> working I think cos the light on it goes out above
> 40km/h (roughly).  However the diff remains locked and
> the ABS off even up to 140km/h (I was hoping to get
> some speed to unlock it)
>
> Observations:
> =============
> When I got home the rear diff is leaking fluid/oil :(
>
> Cause:
> ======
> Had to reverse down a snow covered road -
> unfortunately not enough snow and got caught in
> someones tracks and the car slid sideways and into the
> ditch on the side of the road - more than likely the
> centre of the car grounded out. The two left wheels on
> ice and the two right wheels in a deep ditch full of
> snow - enough that I was just compressing it and could
> not move it.
>
> Finally after quite a few attempts at driving out I
> dug tons of snow out from under the wheels and got a
> Jeep to tow me out.  When I get out I hear a loud
> clicking from the rear - but it does goes away - but
> comes back when I turn left.  When I turn left I feel
> a weird movement from the rear - something to do with
> the diff? Feels nasty (for lack of a better
> description.)
>
> Questions:
> ==========
> * What could it be?
> * I want to sell the car anyway - change the broken
> gasket - new oil and then hope the noise goes away?
> Use Redline oil MT-90 ??
> * Could it perhaps be something like a driveshaft?
> Stuffed CV? Perhaps the oil leaking is a red herring -
> just a broken gasket maybe?
>
> Jase
> '91 Audi S2
> '97 GSXR600
>
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