Re: 4kq differential locks

[raf40@oes.amdahl.com (Richard Funnell)]

It's likely the vacuum solenoids themselves.  I would get a hand vacuum
pump, crawl under the car to the rear diff, disconnect the lines going into
the solenoids (both are right there at the rear diff, white plastic things
with 2 color-coded vacuum lines each) one at a time, and see if they'll
hold vacuum.  When one of mine died, it would hold vacuum in one direction
but not the other.

Assuming your car is like my urQ, the vacuum lines go from the switch on
the console, under the carpet to the left rear fender area where there is a
reservoir, and on down through the floor beside the gas lines.  Obviously
they don't all go to exactly the same place, but that is the general
routing.  Once under the floor pan, the diff solenoids are very close by.
The lines are color-coded (red & green I recall).  I'd start checking at
the solenoids, however, and you'll likely have no need to trace the rest of
the stuff.

>My differential locks don't anymore.  As my Haynes 4k manual doesn't
>cover quattro models, I am at a loss as to where to begin as I don't
>know where the system is nor much about how it works.  When I turn the
>locks *off*, I hear the vacuum being released, though slightly less
>loudly (less vacuum) than when they were working.  Where should I begin
>to diagnose the problem?  How do I determine whether it is insufficient
>vacuum or frozen differential locking pins?  (Probably the former since
>it is suspicious that both center and rear stopped simultaneously.)
>
>Jack Rich
>84 4000S Quattro
>88 Corvette convertible
>90 V8 Quattro

Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL