Brakes locking up when cold....

[nightwalks]

My 1998 Astro AWD's brakes (not sure which axle) lock up first thing in the day when rolling from stop. Only happens a few times, or until I drive a mile or so. No matter how lightly the pedal is pressed, the vehicle stops hard and grabs.
Here's whats been replaced already: Rotors, Calipers, Pads, Both front hoses, slides are lubed and everthing is bled. Rear drums, shoes, all hardware and all bled there also.
I am pulling my hair out trying to figure this one out....any takers?

[Blue Bowtie]

Does the van have an ABS system? Does it have an hydraulic power assist unit or vacuum?

[nightwalks]

All Astro Vans have power-assist, and yes, it has ABS. No codes or indicator lights in the ABS system

[CD Smalley]

Yes they all have power assist. But which kind of assist is what BB was asking? Does it have a vacuum assist or hydro-boost assist?

Sounds like there might be some grease getting out of the rear axle onto the rear pads to me. Just something to look at.

[nightwalks]

It has vacuum power assist. No grease on any of the linings, they have all been cleaned a few times. ????

[Blue Bowtie]

Thanks for the reply. I asked because about 1998-99 is when they were changed from vacuum power boosters to hydraulic assist boosters. Some of the early units had trouble with the valving/reaction mechanism and would "stack up" hydraulic pressure with no pedal input, resulting in locked brakes as you described.

[corning_d3]

Originally Posted by nightwalks

It has vacuum power assist. No grease on any of the linings, they have all been cleaned a few times. ????

You can't/shouldn't clean brake linings with anything. Next time use masking tape over the linings to keep grease n stuff off 'em.

[nightwalks]

The linings are/were new, in "cleaning" them, brake cleaner spray (only) was used to eliminate any chance of stray grease on the surfaces, I am well aware brake linings cannot be "cleaned" conventionally.
I will further investigate the possibility of an ABS or proportioning valve issue. Thanks for your help.

[corning_d3]

Originally Posted by nightwalks

The linings are/were new, in "cleaning" them, brake cleaner spray (only) was used to eliminate any chance of stray grease on the surfaces, I am well aware brake linings cannot be "cleaned" conventionally.
I will further investigate the possibility of an ABS or proportioning valve issue. Thanks for your help.

I was taught that was a no-no as well...

[scottnhalifax]

it could also be the adjustment plugs are missings which causes condensation to get in..
that may be your problem