Diff Lock Problem

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Jan 9, 2011 | 11:25 AM

Supradjza80

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Diff Lock Problem

Hi, I was ice racing my 91 200 20V quattro last night and after a full year of the diff lock working perfectly I am having a problem with it. I have not yet checked my bentley for how the system exactly works but will do this soon. So onto the issue. What happens when I press the diff lock button is the little yellow arrow showing the switch is engaged illuminates but the diff never locks (pumpkin does not illuminate green,diff stays open if tested) and the ABS does not shut off. If anyone knows the best place to start on this issue it would be much appreciated. The only modification to this system is I have cut the Vehicle Speed wire so the diff stays lock above 18 mph.

Last edited by Supradjza80; Jan 9, 2011 at 11:32 AM.

Jan 9, 2011 | 11:38 AM

RB-200 20v

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If I recall correctly, the system is vacuum driven. I suspect your line to the diff is disconnected. Most likely spot would be at the diff itself.

Jan 12, 2011 | 08:38 PM

Supradjza80

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Alright, I have checked the diff and found that the vacuum supply line to the control box no longer supplys any vacuum. I supplied vacuum to the box, pressed the diff switch and it locks without a problem. So, what I need to know is where the differential lock vacuum supply line comes from? I am guessing the vacuum accumulator, but if I could get a diagram so I can start at the vacuum source and work my way back that would be great. Checked the Bentley and found nothing.

Jan 13, 2011 | 07:16 AM

RallyCV

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From: Wisconsin

Check the 2nd post - Looks like its teed from the check valve in the engine bay.

http://www.motorgeek.com/viewtopic.php?f=14&t=36646

Jan 15, 2011 | 07:46 AM

RB-200 20v

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Yep, that's it, that little yellow check valve near the TB. My original broke some time ago, I was able to get a new one.

Jan 15, 2011 | 05:25 PM

Supradjza80

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Yep thats exactly what was wrong with my car. The plastic hose where it attaches to the back of the manifold was cracked. Replaced with a rubber hose to the check valve and its good to go.

Thanks