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Removing stuck caliper pistons


abh3usn
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I'm rebuilding my front brakes. The calipers are off the car. What is the best way to remove the stuck pistons? They are almost even in the bore so grabbing ahold of them with some channel locks is not possible. Any ideas ?

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The really stuck ones can be removed with a grease gun. smile.gif

You make up a fitting that fits where the hose was attached, and then a handheld grease gun will push it out.

You need to clean all traces of grease residue before rebuilding as it will destroy/deform the rubber seals.

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Water or grease is perfect because they are not compressable and as soon as the piston moves the pressure is released. It's safe. Don't be tempted to use compressed air.

When I was rebuilding the power steering unit from my Olds I ran into a similer situation with a stuck piston. It's about 3" diameter and is attacted to the rack gear.

I very stupidly and unthinkingly put the nozzle of an air gun in the hydraulic port hole and gave it a shot of 100 pound air. The piston and gear exploded out of the housing and shot straight up missing my face by inches, dented the metal ceiling and dropped straight down landing on my work bench. It was all over in a split second.

I still sometimes shudder when I think about how close I came to being maimed or killed by just a small momentary lapse of judgement......Bob

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Grease is nasty to clean up, water is probably a better solution, but I put a block of wood in my caliper which restricts movement, and I hit it with air pressure.

Don't start with 100-psi. Some piston bores are 2-1/2" to 3". That produces 300 lbs of force! Start low and work up. KEEP YOUR FINGERS AWAY FROM ALL PINCH POINTS!!!

As mentioned, I cut the caliper-end off of an old brake hose, cleared out the rubber, and brazed it to a 3/8"X6"copper tube. I flared the other end of the copper tube. Now I screw the tube into the caliper, screw the flare into my air hose, and control pressure with the regulator far away. There's no need to stand near the caliper when you charge it. As with all power tools, practice safety first.

Rebuilding your own calipers is a smart move. I did two of mine for $5 each.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: resq302</div><div class="ubbcode-body">But what do you do with the 4 piston style calipers that are bolted together? I have a spare caliper for my 69 charger that I can not get the pistons out since they are rusted in place.</div></div>

Sometimes you just have to bite the bullet and replace the caliper.

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> Some piston bores are 2-1/2" to 3". That produces 300 lbs of force!</div></div>

Actually a 3" piston is a bit over 7 sq inches, but that's an easy mistake. So is playing with compressed air and stuck pistons without very well thought out safety procedures..........Bob

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Hydraulic brake fluid would be very good, too, using the master cylinder, the brake pedal, and your foot. Next time you drive or ride in an A Model Duesenberg, watch the brake pressure gauge. I once had some problem with an Air-over-hydraulic brake system of a Commer truck, so for some reasoning I have forgotten in 30-odd years, I fitted a high pressure gauge to check the pressure between the pedal master cylinder and the power servo unit. It was very significant, and reminded me that I had been a rower at school. It doesn't hurt to flush and change the brake fluid. It may be worth trying to push the piston back in, first. Ivan Saxton

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pumping them out with a hydraulic set up to mimic the brakes is excellent advice. Using air pressure is nasty as it atomizes the remaining fluid but workable be sure to insert a suitable piston stop to ensure the piston(s) do not fly into open space..I like to use a block of wood or leave an old pad still in place..(depends on caliper style)..this will get the piston(s) out to where it can be removed...never grip the piston with pliers if you are going to try to reuse it...never place screwdriver tips into the dust shield lip as a method to pry piston from the claiper. Remember..the piston not only has to move in the bore..the o-ring and its ability to properly seal to the piston on an unblemished surface is the key. The square cut o-ring as it is pressurized in the caliper slot rolls a tad and is the force that removes the pad from rotor contact as it relaxes...so be sure there is smooth piston travel when you clean the caliper bore.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: resq302</div><div class="ubbcode-body">But what do you do with the 4 piston style calipers that are bolted together?...</div></div> You do each one separately. Block one piston with wood, and pressurize the other. When it comes out, clean the bore and the piston real well, put a new square seal and boot around the piston and shove it back in using brake fluid (don't do it dry).

Next, switch the block of wood, holding back the good one and remove the remaining bad piston.

Bob, you're right. (Area = pi*r*r) A 3" bore at 100-psi exerts 700 pounds of force not 300. That's why I always start with low pressure. Compressed air is just too available NOT to use (unless you have something better), and it can be controlled safely.

Dave

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> Compressed air is just too available NOT to use (unless you have something better), and it can be controlled safely.

</div></div>

I was just trying to warn others of the potential dangers of compressed air and the damage it's capable of. I very much know better and nearly killed myself by not thinking.

But you are correct if you know what you are doing and are respectful it can work well.......Bob

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: simplyconnected</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: resq302</div><div class="ubbcode-body">But what do you do with the 4 piston style calipers that are bolted together?...</div></div> You do each one separately. Block one piston with wood, and pressurize the other. When it comes out, clean the bore and the piston real well, put a new square seal and boot around the piston and shove it back in using brake fluid (don't do it dry).

Next, switch the block of wood, holding back the good one and remove the remaining bad piston.

Bob, you're right. (Area = pi*r*r) A 3" bore at 100-psi exerts 700 pounds of force not 300. That's why I always start with low pressure. Compressed air is just too available NOT to use (unless you have something better), and it can be controlled safely.

Dave </div></div>

These are spare calipers that I got to rebuild for my charger. If you unbolt the 2 halves of the caliper, you can not blow air or brake fluid through it since when the halves are together, there is an o ring that allows brake fluid to go to the other side of the caliper. My only possible thing to do is to either: A- send them out or B- put them in a vice and then hook up a air line to the fitting. Downfall with that is that once one piston comes out, you lose all of the pressure going to the rest of them.

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