Brake Fluid Contaminant Containment

[JonJon68]

A friend and I are going to replace my rotors and brake pads tomorrow. I remember reading somewhere on the internet that with ABS systems, it's recommended that we open the bleeder "before" we push the caliper pistons back to make room for the new pads. I Remember reading that by not opening the bleeder we could or will be pumping old sediment into the tiny passages, valves, and pistons risking major damage to the ABS system.
What do you all think about this? My last 1991 GP had all kinds of problems with the ABS and I don't want to chance anything. I inherited the 91 from my brother so it already had ABS problems when I bought it. My current 97 has 147,000 miles and I've not done any brake service since I bought it back in 2004.
Thank you for any info on this subject.

[GTP Dad]

You are better off opening the bleeders and then pushing the piston back in. It is true that contaminates in the brake fluid can damage the ABS especially if it has been that long since the brakes were serviced. You will also be assured that you will have clean brake fluid in the lines once you bleed the brakes. I don't know if you are changing all four or just the front brakes but if you are going to do the job right it would be better to bleed all four and clean the system replenishing it with new fluid. Just remember not to let the master cylinder go dry.

[richtazz]

I 100% agree that it is much better to open the bleeders and then refill the reservoir with fresh clean fluid rather than pushing the old contaminated fluid back up the lines regardless if it's ABS or not. But with ABS, it's almost required, not just recommended, so as to keep these contaminants out of the small passages you mentioned.