A friend of mine (he's a mechanic), told me that he has noticed that if you push the brake fluid back up the lines when compressing the calipers to install new pads on Ford trucks that it mess up the ABS system. He said to open the bleeder screw instead and than replace the fluid when you're done. Anybody ever had this happen or heard of this.

 

I guess there is that possibility, but I have yet to have a problem in the 20 years I've been fixing cars.

 

Same here. I've lost count of the brake jobs I've done and never had that happen, but you never know. I thought it was worth asking

 

not true... the brake fluid will move back and forth when you brake anyway... so there is a constant "mixing" of the brake fluid in your lines.

The one potential issue is if you get air in the brake lines and then push that back up. But on most (all?) systems you can just bleed that air back out without any trouble.

 

I have had a couple of cars I worked on have a master failure after I pushed fluid back through. These were 96 and newer. I figure it has to do with the fluid not bleeding through the master fast enough and it blows the seal. When the brakes are pumped up and correct there is not much fluid thats moving back and forth. And I have done to many brake jobs to count. Now I dont take the chance anymore and just bleed it off into a container and flush new fluid through when done.

 

The seals are designed to allow fluid to flow back across... this is called compensation. On every brake apply there is some compensation due to the dynamic effects of the system. Basically, the pistons will return faster than the fluid flows back. So they replenish (pull some fluid from the reservoir) and then over the next second or so the fluid will come back and push around the seals.

But I'm not disputing your account Jim. If a seal was getting old and had some wear, I could see it having a negative effect. Especially if the caliper were squeezed quickly, forcing the fluid back fast. The seal could be squeezed into the replenish hole and that can take a chunk out of the seal.

 

While I have done numerous brake jobs on various models, I don't pretend to be an expert on ABS and he said it did something to the ABS system. I really can't see what it could be, unless it affects the valving or sensors of the ABS. I should gotten into it a little deeper into the subject, but we got off onto something else and it was forgotten. I tend to agree with you guys that the system was designed to have the fluid surging back and forth all the time, so I don't think I'm going to lose sleep over it. Thanks for the input.


Bob