ABS question on 89 100

[Mike Larosa <mlarosa@v8q.East.Sun.COM>]

Looks like I've been christened to the wonderfull world of ABS troubleshooting 
:-)



Scenario:

Wife's 89 100 Avant,  she starts to hear/feel the ABS kickin on moderate braking
intermittently.  Say's "honey my car's acting up again...."


HHHmmmmmm:

We swap car's and I notice that under moderate braking the ABS consistently
kicks in.

Next day, the ABS light comes on saying the ABS is off.  It did this without 
me hitting the brakes....  hhmmmm thinking maybe I bumped the switch putting
on the radio...

Day three,  Know I notice ABS turns itself off (Light comes on)
when I hit 15 or so MPH.  Hit brakes increasingly harder and don't feel
ABS.  ok, ABS is really off.


Start looking through the bentley, doesn't there is much troubleshooting
I can do without a 725psi pressure gauge or a Bosch ABS 2 led tester. :-(


Possible causes ?

I have fairly worn d60a2's on the front and nearly BFG touring t/a's out back.

I plan to replace the d60's with t/a's in the next month.

Could the tire circumference diff be enough to disable the ABS ?


Does anybody how much a diff will cause the ABS to turn itself off ?

I'm not opposed to measuring the difference to check...


Am I at the mercy of the dealer..... :-(  gulp.


Mike L.
90 V8
89 100 Avant