87 5000TQA Anti-Lock Brake Problem

[Stephen Sherman]

A bit of a long story, but here goes...

The anti-lock (AL) brakes have worked fine on my Avant for 10+ years. 
Recently I had a shop replace a front axle which had a CV joint that was 
going out. When I picked the car up, the anti-lock brakes were going 
crazy. Firing off at slow speed stops even when there was no slippage 
and at higher speeds (20-30mph) it was downright dangerous. Brought the 
car back, the shop said they'd look at it and drove it until then with 
the AL turned off, which I had to manually each time I started the car.

Got it back from the shop again today, and at first all seemed well. I 
can stop with AL active and it isn't firing off all the time. Shop said 
they put the wrong axle in at first and it had a different number of 
cogs on the AL.  On the short trip back from the shop things seemed 
fine. BUT on the longer drive home I noticed that the AL brakes were 
turning themselves off after about 20sec or so. You can work the dash 
button to get them back on again, but 20sec or so later the dash light 
comes on again saying the AL's are off.  I tried working the diff locks, 
and they work fine and go off, but the AL off light comes back on just 
like with the dash switch.

No doubt the shop will work on it again, no charge. But I think this may 
require more knowledge than the guys at this place have. So I wanted to 
ask the AL gurus here what's up?

I believe that the original axle was the wrong one; certain the 
replacement made things a whole lot better. But even with all the 
problems of the 1st axle, the AL wasn't shutting itself off.

What kinds of faults can cause the AL to turn itself off? (And I suppose 
I should ask is it possible this shop just cut a wire so that the AL is 
disabled instead of replacing the axle again. Hate to think that, and he 
did have a couple of new axles in boxes when I showed up this AM, but 
who knows)

Can anyone give me a quick tutorial on what kind of problems would cause 
the AL to turn itself off, and what in an axle change might cause those 
things.

TIA