Rebuilding brake calipers

[Zaddict]

Any tips on rebuiding calipers? Mine are looking pretty rough after 50K miles. Still working fine but I want to do a little preventive maintenance. I'll be changing brake lines and rotors as well. I'm not even sure what a caliper rebuild entails, or a good resource to learn about it. Maybe youtube...

[hugojose]

The so called "rebuilding" is only cleaning the grit on the exposed part of the pistons, cleaning the goo inside the calipers, replacing the seals, and maybe the dust boots on the guides. As long as corrosion is not bad inside, that's it.

You pop out the pistons with air. Even a bicycle pump would do if you can seal enough the air intake.

[Rob@TZP]

They're a relatively simple device, I can't say I rebuilt mine, but I have just put all new rubbers/seals in them...and that's about all there is to it. A bit of compressed air to pop the pistons out (gently), clean them with a sof cloth and check them and the bores for scoring or nasty rust, pull the 'O' rings and replace with fresh ones, using the correct rubber grease. Pop the pistons back in and that's about it, isn't it?

[Freddy]

They're a relatively simple device, I can't say I rebuilt mine, but I have just put all new rubbers/seals in them...and that's about all there is to it. A bit of compressed air to pop the pistons out (gently), clean them with a sof cloth and check them and the bores for scoring or nasty rust, pull the 'O' rings and replace with fresh ones, using the correct rubber grease. Pop the pistons back in and that's about it, isn't it?

If you're going to be using compressed air (how I also do it), just make sure to keep your fingers well clear of the piston and opposite side of the caliper body. If the pistons are gunned up as they will be they won't just nicely slide out. They'll refuse to initially budge them come out like a bullet smashing any fingers that just happen to be in the line of flight. I put a folded up rag against the opposite side of the caliper body to absorb the impact.

Only one piston will initially come out presenting a problem. To get the other one out reinsert the first piston back in just, hold in place with a G clamp (I just hold it in place keeping fingers clear of the other one), and then blow the second one out.

The critical surface is the where the piston contacts the inner seal rubber. I polish up the pistons to look like new on a polishing wheel fitted to my 6" bench grinder.

Assemble with a suitable silicon rubber safe grease. Don't confuse this stuff with high temperature 'caliper grease' which is only for external parts. If unsure get a couple packets of 'Brembo silicone grease' sold in little white packets on eBay. You can then say you have Brembo brakes. Don't just use brake fluid for reassembly, its water soluble and any lubrication and rust prevention to the outer seals and exposed piston it may offer will disappear in the first shower of rain.

On a performance oriented bike, I overhaul the calipers with every brake pad change. As that also requires bleeding the brakes, in effect a complete brake overhaul to as new condition. Very little additional work, and just the added cost of the seals.

[andyoz]

yep as above as I did not hard and I replaced the pistons with stainless ones..

[Zaddict]

Thanks all, very helpful info. I believe I have a clue now.

Regarding using compressed air to pop out the pistons - what sort of an adapter are you using to connect the pump to the calipers? Maybe I have to get creative? I suppose I could just modify a little rubber cap to the mate the pump outlet to the brake hose inlet or bleeder nipple.

[Freddy]

Buy a cheap air nozzle gun and assorted attachments like the following. Made in China so not expensive and really useful for all sorts of things. Sold in any 'big barn' hardware store or large auto accessories store.



Sometimes among the screw in attachments is a rubber ended stubby thing, if not just use the fitting like in the picture. With the bleeder screw done up, just shove the small tapered nozzel firmly into the hose connection and pull the trigger. Doesn't matter it leaks a bit, just remember to keep your fingers clear.

[Larry02ACR]

I left one of the brake pads in place when I used compressed air to blow out the pistons.

There was just enough meat on the pad that both pistons were extended almost all the way out when they contacted the brake pad. One piston shot forward pretty fast and once it hit the pad then the other one moved out. Afterwards I removed the pad and was able to wiggle the pistons free.

The front pistons I got lucky and was able to clean/polish them up back to like new condition with a little elbow grease and metal polish.

I ended up putting NOS pistons in the rear caliper. Brand new seals all around.

[hugojose]

I can do it with a bicycle pump by plugging the line connector with a bolt, and then unscrewing the nipple, I use the conical plastic adapter the pump came with, simply held against the nipple hole while I pump, however this is fumbling a little, because sounds like needing three hands, if you don't have something to hold the caliper steady.

It is a lot easier using a cheap small compressor tire inflator, because you don't have to pump. With inflator running, hold the caliper in one hand, and apply the adapter on the nipple hole with other hand, until piston pops.