Rear locking differential 1988 90Q

Tony Hoffman auditony at
Tue Aug 7 10:51:07 PDT 2012

I've repaired several of these. First thing to do is figure out where it's
leaking on the "off" side of actuation. Is it leaking at the broken off
tab? Is it leaking out of where the boot should be? I've repaired the
missing boot with a rubber cover designed for the end of a silicone tube.
However, they disintegrate after about a year, so I'm not too sure what
I'll do long term.
Here's a pic:

As for the crack, I've used epoxy from teh inside and outside, and had
really good results. The part where the pin goes on, that unscrews from the
rest of the actuator. You will have a stud left sticking out, that is not
removable. It's part of the rubber bellows that actuates the lock.


On Tue, Aug 7, 2012 at 10:28 AM, Radek <radek at> wrote:

> So now that the diff is out, we can clearly see the cause of it being
> locked all the time.  As I suspected, the plastic vacuum actuator has
> broken off at one of the three screws and is moving around a bit.  I used a
> vacuum pump:  it seems to be holding vacuum when the "on" side (yellow
> striped hose) is activated, but doesn't hold it when the "off" side (blue
> striped hose) has vacuum applied.  This is odd, because I would expect a
> single membrane inside, so if it's broken there would be no vacuum held on
> both sides.  To put things differently, the actuator has enough strength to
> engage the lock, but not enough to disengage it.
> I would like to take it off the diff to clean, inspect and repair/replace.
>  Here's the question:  how do I separate it from the diff?  The actuator
> arm has a pin at the pivot point, but it seems to be permanent.  Can I pull
> the arm out of the actuator or out of the differential perhaps?  Bentley
> does not offer any help (or I haven't found it).

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