I would like to replace the front brake pads and the brake fluid on my 1997 Legacy L with ABS, but warnings about working on antilock brake systems and inconsistent advice on the web have deterred me. The Haynes book mentions no special procedures for the Subaru ABS.

 

I've read that I should not force the pistons into the calipers with a C clamp, as this will push dirty brake fluid into the ABS.

 

Someone recommended relieving the fluid pressure by opening the bleed screws. However, I had a dealer replace the brake fluid, but he did not flush old fluid through the bleed screws on the calipers, saying it's too problematic if air gets into the ABS. He only removed old fluid through the master cylinder with some unspecified "machine" and replaced it with new.

 

My three questions are:

 

1. What is the correct way to back the pistons into their bores?

 

2. What is the correct way to replace the fluid in the ABS and bleed the system?

 

3. Did the dealer replace enough fluid or should he have replaced the fluid in the calipers and brake lines near them?

 

Thanks for any help.

First of all my experience is limited to a 93 Legacy with ABS. I have not had the pleasure of replacing my disc brake pads yet, but from doing the job on an earlier Subaru model, the FRONT caliper pistons needed to be turned, or rotated into their bores. This was due to the emergency brake mechanism inside the (front only) caliper bore. With ABS there really shouldn't be a dirty fluid contamination problem because the fluid will mostly bypass the ABS internals. The fluid does pass through the ABS unit, but not throughout the whole system. The fluid only passes through all the ABS internals if the system is activated. This is my take on the issue, I hope it helps.

i just changed the rear pads on my 97 obw with abs. haynes says absolutely nothing cautionary about pushing the fluid back, but i have heard that is bad. i looked through the factory service manual, but their procedure for replacing the brakes assumes that you are going to install a new set of seals in the caliaper, so that is how they take care of getting the piston back in the bore.

 

what i finally settled on was to drain the brake fluid from the reservoir with a syringe, filled it with clean fluid, then bled the system. after bleeding it, i replaced the rear brakes, using the c-clamp method to push the piston back into its bore. my thinking was that i would only be pushing clean fluid back through the abs unit...

 

on this car (pretty sure), the emergency brakes are a set of drum brakes within the center of the disc on the rear wheels - you won't have to worry about turing the caliapers back in...

Sounds like a good move. New fluid bled through, so when does pass through the ABS unit, at the least it is new, clean fluid.

 

Glad it all worked out.

First answering your questions:

 

1. You can compress them with a c-clamp just make sure to use the old pad to push on, sometimes I have just used hand pressure. Open the bleed screw and bleed the brakes after doing the brakes.

2. Replacing the fluid by syringing out the master is probably good enoughfor maintenance, however bleeding the lines is the only way to get all of the fluid out. If you are doing the front pads you might as well flush the lines.

3. Replacing the fluid like the dealer did is good enough for maintenance, but if you are doing the pads you will flush the lines out anyway.

 

The dealer saying it is problematic to get air out of the lines while flushing is BS. You are pushing fluid through the lines, not air. And if that was the case how could you ever change a caliper? It is just easier and cheaper to do it that way - kind of like changing the trans fluid and not removing the converter, it is not worth dropping the trans to get every drop out during maintence, get most of it and call it good enough.

 

Our brake fluid is hygroscopic, meaning it takes on water (so your brake components don't rust from the inside out). Replacing your fluid is done to remove the fluid that has taken on water, and to allow future capacity for holding water. Changing the Master will eventually work its way toward that end, just not 100%. But particles other than water tend to stay deeper in the system.

 

I have heard of several people with ABS problems after compressing the calipers without opening the bleed screw. Changing the master fluid right before doing the brakes and compressing the caliper without opening the bleed screw will still push the crud in the line back through the abs unit. Solids settle to the lowest elevation, any rust and stuff will settle to the calipers, only flushing will take that away.