Any tips for a Stuck Caliper Piston?

One of my caliper pistons is stuck in a semi-retracted manner...not all the way in and not all the way out. I assume I compressed it with uneven force when preparing to rebuild. I've tried gentle compressed air. The other three function fine but this one won't budge in either direction, although I have not used excessive force.

Any ideas?

Pic attached, the stuck piston is bottom right (let me know if it doesn't show up!

 

The cylinder wall is probably rusted back where you pushed the piston to. Time for a new caliper. Or better yet, a set.

 

Reinstall on the truck along with the other three and fill brake fluid, start truck and pump brake pedal easy and should push it back out. Make sure old pads are in there so doesn't push it to far and let piston come out. Before trying to retract it again carefully lift the piston boot and try to get brake fluid all around it and kinda acts as a lube when retracting piston without damaging the rubber boot.

 

order rebuilt from local autoparts store, turn this one in as a core...

 

I may give this a shot since I'll be waiting to get a new caliper shipped anyway! I have extra seals and dust boots on hand so I don't have to worry much about damaging the existing rubber components

 

Just replace it or get new pistons and seals and rebuild it yourself. Chances are it's cheaper just to replace it. They almost never work right after seizing up.

 

Since you were going to rebuild it yourself anyway.......

With the caliper flat, pull the boot out of the way as much as practical and soak around the piston with kroil similar quality penetrant. Let sit overnight.

Put something flat on the piston face, like an old pad, and give it some light raps with a hammer. If it doesn't pop free,

Set the caliper in a vise in such a way that the piston is clear. Put the brake pad across the face of the piston, then put your C clamp on it, and crank away.

At this point the worst that happens is you install a reman unit anyway. So if getting it freed up doesn't work, or happens to damage the bore more than you want to mess with, you aren't really out anything.

Let us know if you have success.

 

That's pretty much what I did. I hooked it back up to the brake line and pumped the brakes slowly until resistance returned.

Nothing.

At this point it became a learning experience. I removed the caliper, bled all the fluid out of it, took the two halves of the caliper apart, put a rag over the stuck piston and hit it with the hammer alternating with PB sprays and hammer raps. It finally went in and allowed me to use around 20 psi of compressed air to push it out.

There were some scratches on the cylinder wall so, I followed this advice:

With the amount of effort the slider pins took to get out, I'm happy to pay the 100 for a rebuilt caliper with fresh slider pins. They came with pads too that I won't use, but I'll happily utilize the new cotter pins and whatever the "W" shaped pin is called.

 

next time, just get the friction ready caliper...you don't pay for a pad you don't want. I changed one out on the JK Wrangler a few weeks ago, now I just have to use my store credit with Rock Auto for the return.

Howard

 

Yeah, Impatience dictated I get the loaded caliper as it was the only one available locally. When I replace the opposite caliper, I'll make sure to get one for a bit cheaper that isn't loaded from an online source.

Can you let me know how the one from rock auto came? Powder Coated? New slider pins? New W clip (I assume these would come with pads not the caliper if it is friction ready)?

The one I got came with new everything and after having to use a punch to push the original slider pins through, I'm happy for that. Plus the break line/bleeder came already covered so painting over the fresh powdercoat was a breeze.

 

Also, new one installed:



Edit: I know I installed the slider pins backwards. That was fixed after I took the pic

 

It came looking like the one that came out, and since it was for a jeep, the hardware pieces were different. I also installed a new brake hose at the same time and flushed the braking system. All I had to do was install the pads, hook up the line with included washers, bolt it on and bleed the system.

 

Pic dump of the project, because why not?


From bottom left to right to top- Brand new rotor with intact rust coat, old OEM rotor after 95K, new rotor with rust coat cleaned off

In case anyone else needs to see the OEM installed parts for reference:

Removing the warped, rusted slider pin:

17mm bolts holding caliper to hub:

12mm bolt holding brake line in place:

Using the bolt method to remove the old rotor:

New loaded caliper:


One thing I learned is if you have to remove the break line, spray the nut with PB or equivalent and let sit at least overnight. Then use a 10 mm *flare* wrench to break it free. Doing it any other way seemed like a good way to round off the nut.

 

Thanks for the info! The passenger side caliper was in significantly better condition. Far less rust and I used a bench grinder/brush to clean and restore the slider pins. Would the drivers side weight cause more rust and wear on the drivers side caliper?

From here on out, I may pull these pins and re-lube with brake lubricant every time I have the wheels off to keep them from seizing like that were at the start of this project.

 

Found this to be an interesting article, on what to use to break loose those rusted nuts and bolts. "Machinist's Workshop" recently published information on various penetrating oils. The magazine reports they tested these products for "break out "torque" on rusted nuts and bolts. A subjective test was made of popular penetrating oils, with the unit of merit being the torque required to remove the nut from a "scientifically rusted" bolt. Average torque load to loosen nut:

No Oil used ........................516 foot pounds
WD-40 ..................... ........238 foot pounds
PB Blaster .........................214 foot pounds
Liquid Wrench ......................127 foot pounds
Kano Kroil .........................106 foot pounds
ATF/Acetone mix...................... 53 foot pounds

The ATF/Acetone mix is a "home brew" mix of 50/50 automatic transmission fluid and acetone. Note this "home brew" released bolts better than any commercial product in this one particular test.
Our local machinist group mixed up a batch, and we all now use it with equally good results. Note also that Liquid Wrench is almost as good as Kroil for 20% of the price.ATF/Acetone mix is best, but you can also use ATF and lacquer thinner in a 50/50 mix. ATF = Any type of Automatic Transmission Fluid. https://www.youtube.com/watch?v=urK2EsZn4pQ

This version of the story was in one of the Military Vehicle Club newsletters

 

Large metal "C" clamp.