I recently picked up a 1986 5000 Turbo Quattro wagon, and am trying to work out the bugs! I have a problem with the locking Diff function. When the car is running, and the selector switch on the dash is vertical (ie off), diffs are locked - at least the rear diff is for sure. There is also a constant hissing of air escaping from the switch. I know it's vacuum controlled, but is that normal?
If I turn the switch to the "1" position, the switch stops hissing, but both green LED's illuminate to about half brightness. Then if I move the switch to the "2" position, either nothing changes, or the green LED for the #2 position illuminates as it should.
I removed the switch and cleaned up all the contacts, and inspected the vacuum lines, but it didn't do anything.
Is there a way of testing the switch? Do the switches break often? If it's not the switch, what else could it be?
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Joined: 3/9/2004 From: Swamplands of NJ Status: offline
It sounds like the switch might be defective, it shouldn't be hissing. As far as I have read the vacuum actuators are prone to problems and is one of those things to check when buying a used Quattro. The manual should have steps for testing the switch.
I am pretty convinced it's the switch as well, but I have yet to find a test for it. The Haynes manual doesn't include the Quattro versions, so there's no test for the switch.
All the things I read on the internet make really helpful comments like "Test switch, and replace if bad."
Is there anywhere that would sell reconditionned switches?
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Joined: 3/9/2004 From: Swamplands of NJ Status: offline
That's part of the problem with the non factory service manuals, there are too many blanks or "we suggest that you take it to a dealer." I have a Bentley (OEM) Audi 4000 manual and I am pretty sure that there is a section to test the switch. If I have time and don't forget I will flip through the pages, the 4KQ and 5KTQ both use the same switch.
It is my intention to get a Bentley manual, but right now I have to spend the money on things like new wheel bearings and this switch. I appreciate all the help!
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Joined: 3/9/2004 From: Swamplands of NJ Status: offline
I checked my 4CQ manual and unfortunately there is no procedure to test the switch, just disassembly instructions. However the indicator lights are switched by vacuum actuators one in the trans and the other in the diff. If both indicators lights work then the servos are engaging the locks. According to manual you also need strong vacuum to engage the servos.
I did work on that vacc unit, lines and all the system for lock on 5000TQ 87. Check if both are jammed full lock.
The center unit is on the passager side up from the CV joint on the tranny. The rear one is on the passs side in front of the rear CV joint.
Center lock: Open the vaccum switch and swap the red and green;its the center lock vac lines, the vaccum unit on the tranny should toggle to the other position(switch vertically), car running. See under the car if the vac unit operate or go for a ride. If center lock , the steering is harder to operate , espec on hard corners.... Do the same for the rear lock, the two other vacc lines... To check the vac units , just block on hose and try to move the unit, should be hard to move, and want to go back on his previous position if no leak on the unit.
you can access the rear hoses under the rear seats , pass side.
Check mecanicaly if the level rod is jammed; located on the passager side on the tranny, engine not runnig. you should be able to move in two way, the vaccum unit.
Posts: 758
Joined: 3/9/2004 From: Swamplands of NJ Status: offline
In "The Audi Quattro Book” the author recommends checking the Quattro system by putting the car on a lift and checking to see that all the vacuum servos are working properly. You can also use a tune-up type hand vacuum pump to check the switch as well as the workings of the servos.
Printable Version
1986 5000 TQ - Problems with Locking Diffs - 
