95 Voyager - ABS issues

Hi, wow I am glad I found this place I have been searching the internet for a couple days trying to figure out what is going on with my brakes.

We just recently purchased the van and it developed a shimmy during braking and the pedal would drop and sounded like the ABS was kicking in. Well easy fix " I Thought " I assumed the ABS was kicking in because of the warped rotors and would quit after I replaced them. Well it didn't.

It only seems to do it while I am braking down hill, the pedal will drop and it brakes make a strange noise. Keeping steady pedal pressure they will return and pulsate. Now this is on dry road at normal speeds. No need for the ABS to be working.

We took it to a mechanic and he said I got air in the ABS system " I replaced the master cylinder ", possible I am less than a shade tree mechanic so its possible. But today the ABS light came on the the brakes where great lots of pedal and no dropping.

So I am looking for advice, Is it AIR? it does not do it all the time. Is it a wheel sensor? Is it safe to drive with the ABS light on?


Thanks
Roger

Ok here is some other info that might help. It will only do it from 35-50 mph I have been paying close attention and it seems strange but it only happens in that range, above 50 and below 35 it wont do it.

Anyone?

Does your van have the rear brake modulator on the rear axle?