Caliper pistons seized

[T.Hanson]

Admitting I read the FAQ but missed the part about inserting a block of wood between a piston willing to move before the seal completely clears the bore.

Somehow on previous rebuild missions I got away with using a needle nose vice grips, compressed air. This time, no joy.

For the sake of pure stubborn, and curiosity how commercial rebuilders remove the pistons, is there a trick, method out there ?

I suppose, push comes to shove, the drat thing can be installed to reattempt the wood block routine.

[Qwodracer]

Here's what I did:

Fill the whole caliper with PB blaster, spray around the face of the seal also, let sit. Or if you have a gallon bucket full of PB blaster just drop it in. Let it soak.

I used a air hammer attatched to a proper size socket, to push the piston in first (now it's unsiezed) then I just applied air. One didn't come all the way out so I pushed it back in a few times and eventually it came. (Not a proffesional, just how I did it)

[Mike W.]

Yeah, I went thru the drill earlier this year. A number of the caliper pistons weren't very happy about coming out. Often one side or one on a side would. It was a slow drill, but I could usually move it some. I would then push it back in with channellocks and try again. And again, and again, sometimes many times. I of course had to reinstall the ones that did cooperate and use a wood block between the halves to keep pressure in there. The fronts having more than one piston per side was more difficult, but mostly just slow.

How do commercial places do it? I don't know, but I would guess they would split the halves, bolt them to a jig and apply hydraulic pressure with a fluid. BTW, I was amazed at how much time I had in it doing all 4 calipers. It was a slow process. Curiously even without regular fluid changes all the rust was on the outside of the seal, it was bad boots and moisture in the air that caused the problems. One piston was less than perfect, but still entirely usable.

[T.Hanson]

Thank you for reasons to fight on.

I wonder how many Fivers are stubborn motivated enough these days to engage in such projects.

A year or three ago I cleaned and painted a set of front calipers. The pistons were inserted in the bores without the seals to fit in the boxes. Having to use one while fooling around with the seized pistons I was not amused seeing the rust film in the bores.

The lesson seems to be rebuild and reinstall, or spray some kind of lubricant on the surfaces if kept in reserve.

[Eta power]

I like working on my cars, but I also like going to car events and not spending a week rebuilding one caliper. I have either sourced rebuilt or good used calipers to replace the old rusted-to-shit ones that I have run across.

The only suggestions I have would be:

1) Leaving the caliper connected to the car's braking system while trying to extract the stuck piston, as mentioned previously.

and

2) 50/50 ATF and Acetone is said to be one of the best penetrating fluids.

Good luck and happy wrenching!

[T.Hanson]

It is a personality quirk, being stubborn enough to select spending the week rebuilding a caliper. I agree a reasonable club member might opt to rub money on it, buy a rebuilt and go on a road trip.

Thank you to those who suggested penetrating oil soaks and dynamite. I did the soak for 24 hours. When it didn't magically work I had given the 1500 pounds of pedal pressure pushing the pistons clear of the caliper bores more thought.

We won. That is the solution for fellow eccentrics. Brake pads removed, calipers in place, pump the pedal until all of the pistons are well clear of their bores.

The reason a piston leaked to start the show : I failed to notice two pits obviously large enough to matter.

[PatinaBeforePolish]

I like working on my cars, but I also like going to car events and not spending a week rebuilding one caliper. I have either sourced rebuilt or good used calipers to replace the old rusted-to-shit ones that I have run across.

The only suggestions I have would be:

1) Leaving the caliper connected to the car's braking system while trying to extract the stuck piston, as mentioned previously.

and

2) 50/50 ATF and Acetone is said to be one of the best penetrating fluids.

Good luck and happy wrenching!

I attempted rebuilds picking the best from 2 sets and was just not happy with the results. The rebuilds from aftermarket like RockAuto are junk and destined to fail. I gave in and bought a new set from the dealer and saved lots of time and frustrations. Expensive but I hate taking any chances with brakes.

[T.Hanson]

Perhaps we agree on different different strokes, and my not disagreeing with your adequate budget method to buy factory new calipers. Minimal risk of problems involving safety,... in trade for dinero.

I had to look. $437 each impressed me. Plus the cheap ones you refer to look available for $47.

My experience rebuilding them myself three times has never resulted in a failure. Predicated on paying attention to any warnings. Pedal pulsating, disc scraping noise, pedal dropping or softening. Normal city driving, pulling wheels every once in awhile to visually check things and wheel bearing, suspension parts. Anticipate worst case scenario, failure, the emergency brake handle will suffice to land safely.

As reported, the condition of the pistons, bores and inner O rings must be as new. Smooth, no visual grooves nicks or pits. I can do that. As well as cleaning and assembling, learning more by doing. And asking.

I was built in 1946, suspecting it has something to do with my current opinions, preferences, eccentricities, synonym for drooling booby compulsed to write these posts.

[PatinaBeforePolish]

And the "teachable moment" here for any observers is FLUSH AND CHANGE YOUR BRAKE FLUID EVERY YEAR!!!! My car came with service records back to new and it's really interesting to see the comprehensive service schedule BMW had in the good ol days. The second owner followed more basic maintenance and went about 5 years between changes. The fluid was dark with crud in the bottom of the reservoir when I bought the car which could have been avoided with regular changes.

[RonDwyer]

Kroil makes stubborn pistons come out better than any other product I have used. I split the calipers and grab the end of the piston with the vise just enough to enable the piston to be rotated back & forth in its bore. If it takes too much force, add Kroil and let it sit for a while. Always add more if a dry spot is seen. And wear gloves, that stuff has some nasty stuff in it.