Luxus Panzer

<center><img src="http://s2central.net/images/diff.jpg"></center><p>
If does not feel like my rear diff is locking when I toggle it. when I press the diff lock switch the yellow triangle in the button lights up, however...the light that is green in the pic attached (one in the diff) does not light up, nor does the "antilock off" light in the dash come on.

The yellow triangle light does go off at 25km as it should. The Antilock light is not burnt out and does work.

Is this a common problem, any usual suspects to have a look at?


thanks all

dtompsett

Green light is triggered by a switch in the rear diff. If you get under there, you'll see an electrical switch on the back of the diff, on the drivers side. If the diff doesn't lock, the switch doesn't close, which means no green light, no ABS shut-off.

The car will still trigger it's 25km/h unlock sequence.

Could be:
#1 - rusted bracket flexing when trying to move the actuator to lock the diff. (that's very common on our cars because of the large amounts of salt they put on Ontario roads. ALL of my quattro cars have had this problem... 3 90q's and a 4kq. Only way to solve it is to buy a new bracket, or make one from some sheet metal. It's a complex shape though. If you do it from some heavy-gauge steel, you can ignore the bottom curved section that holds it to the 3rd bolting point on the diff.

#2 - actuator could be bad. It's a two-way vacuum actuator. If the seals go bad, then it may not generate enough push/pull to move the diff arm.

#22 - bad vacuum module under the rear seat. Unlikely, but it's happened. My first 90q had a bad module. Wouldn't release the vacuum to the lock side of the actuator, and wouldn't send vacuum to the unlock side, so the diff was locked all the time.

- rotten vacuum lines could also be a culprit.

<img src="http://pictureposter.audiworld.com/79384/reardiff.jpg">

Luxus Panzer

the switch is #2?

dtompsett

it would be under the electrical section.

I doubt it's just a switch problem. If the diff is locked, you can tell when you drive it. You don't need a little green light to come on to tell you if it's locked.

Solve the locking problem first, then find out if the switch works. More than likely, you'll need to get underneath and check things out. Which will suck, cause I bet you've got tons of snow there.

independent77

My 'locker' failed last week, Found out it was a disconnected vac line under the hood.

Luxus Panzer

what kind of vac readings were you seeing when problem was fixed?

independent77

The difflock vacuum system is fed from 1 small black vac line.
Starts at the IM, passes through the firewall Under the heatercore lines. Under dash(not sure exactly where) and along the driver side of the car(under the plastic trim)
That line then connects to a T, and one side connects to the VacSwitch(under the seat) the other line from that T runs to a Vac 'accumulator'(located in the pass rear fender-trunk)


with the diff disabled, you should have vac on the blue line, with it engaged, Vac on the yellow line.
Its quite possible that i have the 2 colors reversed.

hope this helps.

90q UK and ROI

if it's only the bellows on the acctuator shaft losing vaccuum (won't engage) and especially if the collar on the shaft end is intact, I have just repaired mine with a wrap of loom tape (rubberised and sticks to itself) and some small zip ties. you have to leave it quite long and baggy, so it can concertina in and out with the shaft : )

Luxus Panzer

Thanks...I fixed it almost FIVE years ago, lol

90q UK and ROI

Yeah, Thanks for replying, I realised that... but could not find anywhere else, more appropriate, to post for anyone else with a similar, extinct, diff lock acctuator vac leak ploblem; given scarcity of these parts.

PS It turns out that: BOSCH part no. 3 340 522 025 is more or less a straight replacement for the rod seal with a little trimming