adh__D

Over the weekend I began the process of replacing worn wheel bearings on the front side of my XJ.

But, despite my infinite wisdom, I depressed the brake pedal while the caliper was off the rotor and so now my brake pads on the front passenger side are stuck together

I went out and bought a brake pad separator, but, as i suspected, the hydraulic pressure is too much for my 170 lb frame to overcome.

So my question is this:

How do I reset my brake piston so that I can put the caliper back over the rotor?
Will I need to bleed my brake lines to release the pressure?
Or is there a faster way?

I added a pic for reference.

Hopefully someone will have time in-between fireworks and beer to answer my question!
Brake Caliper with pads removed. Brake separator w/ crowbar used as a base.

trans_am7935

You could crack the brake bleeder but should not have to, you may have some corrosion in there. If it were me, I would crack the bleeder to see what comes out, and if anything other then clear I would bleed the brakes. If rust comes out or chunks of any kind, I would pull the piston out of the caliper and check for damage or rust. If rust is present, sand it down, pop it back in and all should be well.

Remember brake fluid should be changed ever 2 years. When water gets inside, it tends to cause rust. Since brake fluid is hydrostatic, then it will start absorbing water from the atmosphere from day one.

adh__D

Alright.

I opened the bleeder and the fluid came out looking clean, I just bought the jeep so im going to bleed the lines anyway, just to have a baseline.

The thing is, even with the bleeder open, the caliper piston isnt budging. Not one bit. I dont think its rusted, becuase I was not originally having any issues from it, the wheel bearing was what i was repalcing.

Am I missing a step? all i need to do is relieve pressure enough to retract the piston and fit the caliper back over the rotor. the part I dont know is "how"

fb97xj1

If cracking the bleeder, or even pulling the line from the caliper do nothing, all i can think of is the piston shifted just enough to get hung up in its bore, or a speck of dirt or rust found its way between the piston and bore. The piston isnt hung up on the seal somehow, is it? I have never experienced these issues, but that is all i can think of. Look at it from the sides and see if it looks crooked.
You could place a board over top the piston and try tapping it with a hammer a couple times, and hope it cooperates. No gaurantee it will work.

adh__D

Yea it looks like i just earned myself a new set of front calipers.
I agree that applying the brakes probably did unseat the piston.

Didn't budge w/ bleeder open.

Didn't budge when disconnected from line.

Thanks for your help guys

Larry's XJ

Are you using a C clamp to compress the piston while bleeder is open ?

DFlintstone

Was wondering. If you pushed the piston all the way out of the bore, (or darn near), maybe you got it cocked on that very first shot at pushing it back.

Maybe hit the pedal and push it out again and be supper careful to gently tease is all around working it in. 12:00, 6, 9, 3. It's my bet it's binding.

Like said you can try tapping. Neet thing there is you can feel what's happening. Tapping towards the bind will feel hard/solid, where as taping the outer might feel soft, like it's doing something.

trans_am7935

Before getting a new caliper, if you managed to get the brake pads off, just pop the piston all the way off, and take a look inside. It is VERY easy to place it back in after resetting it, it could just be crooked in the piston sleeve. The fluid will come rushing out, so either clamp off the brake line (not recomended) or pull the brake line and plug it. If you have an air compressor, it will do the job to get the piston out with the caliper off by shooting air into the brake line hole. If not you can just press the brake pedal with the caliper off the brake disc and it will come shooting out, literally shooting out. You will hear a loud BANG and it will be out, along with all your fluid.

If you want you can replace the parts inside the piston like the seals, and the dust boot with a rebuild kit from an auto parts store. They cost like $3 - $5.

Or you could just replace it. I myself love to wrench and figure out things about my Jeep, so I would put in the wrench time.