Caliper Refurbish

[Rasputin]

I use about 25 grains of Hodgon H4895 with a blasting cap. I have NEVER had a problem getting the piston out. Of course it can take a few hours to find the pieces of the caliper and the piston.

Enough air pressure can do some serious damage too. They pop out with quite amazing force, although not quite like what you describe.

[crazy steve]

Enough air pressure can do some serious damage too. They pop out with quite amazing force, although not quite like what you describe.

Yep, you can get hurt using compressed air, besides having the piston fly off someplace and get a nick in the sealing surface, converting it to junk...

[sparkfly88]

I've always just used the master and fluid....and pump the piston out.
It's there, why not use it?
plus, it flushes the system at the same time


I swear by the Permetex Synthetic green goo!

There are MANY cars(cages as I see on the forum) driving around that I've worked on with the stuff on the brake slides, etc.

[clcorbin]

Yep, you can get hurt using compressed air, besides having the piston fly off someplace and get a nick in the sealing surface, converting it to junk...

Yup. That is why that:

1. A block is used that only allows the piston to JUST exit the caliper
2. The caliper is wrapped up in a clean shop towel
3. Air is BLOWN into the port. The air gun is NEVER sealed up against the caliper!

This method works very well. Like pretty much most tools, improper use can lead to a great deal of pain. If you do all three items above, you can safely use compressed air to remove the pistons.

An alternate method would be use water (or oil) in one of those pressurizable spray bottles. Fill the bottle 3/4 full of liquid of choice and fill the caliper with it as well. Pressurize the spray bottle to 50psi or so and then seal the blow gun tip on the spray bottle to the port on the caliper and apply the pressure. The first two items on the list above are still required.

The advantages of this method is you are dealing with pressurized water which does NOT "explosively" expand (neither does air from just compression, but it DOES expand very rapidly!) when the piston comes out. Now you have a caliper full of water, but you were disassembling it for a full cleaning and rebuilding, so that is not an issue anyway. Just don't set it down and leave it soaked in water after the piston is out. Dry off the piston and the caliper thoroughly (compressed air???) before calling this part of the project done.

Oh, and do this outside! You WILL get water everywhere with this method.

[clcorbin]

I've always just used the master and fluid....and pump the piston out.
It's there, why not use it?

Two reasons:

1. Brake fluid is nasty crap. I DON'T like getting that stuff all over everything. Or myself for that matter.
2. You can only do one side of the front brakes, so you still have to have an alternate method for the side that didn't pop out. Unless you have a special cap or single brake line to work the other one out.

As for flushing, well, I usually clean the master cylinder out as well, and the brake lines are drained as well. So only new fluid is in the system when I rebuild it. I just can't see taking the time to clean and rebuild the calipers like that then pushing dirty fluid through them. At the very least, flush the brakes BEFORE popping the pistons so you don't push all that old crap through your freshly cleaned calipers.

[crazy steve]

Yup. That is why that:

1. A block is used that only allows the piston to JUST exit the caliper
2. The caliper is wrapped up in a clean shop towel
3. Air is BLOWN into the port. The air gun is NEVER sealed up against the caliper!

This method works very well. Like pretty much most tools, improper use can lead to a great deal of pain. If you do all three items above, you can safely use compressed air to remove the pistons..

Yes, doing this will work... right up until you run into a piston that's thoroughly frozen in the caliper...

I'll use the above air method for the first try; but if it fails (and it can), your choices are more air pressure (ensuring that the violence with which the piston exits the caliper goes up) and/or abusing the piston with pliers.

Using a grease gun doesn't have these shortcomings. Even the most stuck piston will come out slowly and smoothly, you just have to clean out the grease afterwards...

[clcorbin]

I'll use the above air method for the first try; but if it fails (and it can), your choices are more air pressure (ensuring that the violence with which the piston exits the caliper goes up) and/or abusing the piston with pliers.

Using a grease gun doesn't have these shortcomings. Even the most stuck piston will come out slowly and smoothly, you just have to clean out the grease afterwards...

I agree Steve. Thankfully (???), I live in the high desert, so finding calipers that corroded is actually very rare! You wouldn't believe how clean the pistons and insides of the calipers were when I rebuilt them this winter. I KNOW it was the first time they had been cracked into in at least 24 years...

[crazy steve]

Thankfully (???), I live in the high desert, so finding calipers that corroded is actually very rare!...

Boy, that sure isn't the case in the Northwet... er, I mean west...

I'll bet I end up using the grease gun about 70% of the time. Of course, I usually buy dead and/or seriously neglected bikes, so that enters into to it also....

[clcorbin]

Boy, that sure isn't the case in the Northwet... er, I mean west...

I'll bet I end up using the grease gun about 70% of the time. Of course, I usually buy dead and/or seriously neglected bikes, so that enters into to it also....

I've seen some of the pictures! When I rebuilt mine, I was really worried about it. When they came apart, the insides of the calipers looked brand new with very little crap in there and no corrosion on the aluminum. The pistons had some surface rust inside the piston cup, but nothing on the surfaces that are inside the caliper or on sliding surfaces of the piston.

Frankly, I was a bit shocked how clean they were. I can say that I have flushed the brake fluid at least 3 times in the last 24 years, so given how dry it is here, that makes a big difference. Of course, this is one of those places that in the winter, you can dry out a wet can of brake fluid by opening it up and leaving it out on the counter for a few days... We are usually in the low 2 digit and sometimes even single digit humidity during the winter.

[MPittma100]

What Would Happen?

Has anyone cleaned up the caliper bore or piston with media blasting (i.e. glass bead)? I am wondering if this would be a viable cleaning option.

MP

[Courtney]

Hmmm, good question. I've blasted aluminum heads and stuff but nothing that uses fine machined surfaces like that. I'd be more tempted to soak the caliper in carb cleaner dip. You could remove any rust on the piston with Evaporust which is harmless to steel but eats rust.

[crazy steve]

Has anyone cleaned up the caliper bore or piston with media blasting (i.e. glass bead)? I am wondering if this would be a viable cleaning option.

The piston would be a no-no, as the surface finish on those is designed to be smooth enough to move in the seal, but with enough 'stiction' to grip the seal and retract the piston when the brake is released. Generally, any damage on the sealing surface means the piston should be replaced.

The bore is another question.... This isn't a sealing surface, more like a 'guide' for the piston. As long as the piston can move freely without too much slop, the bore isn't critical. Now, the recess the seal fits into is another matter; I don't think you want to damage that area at all.

If you found a bore with heavy corrosion/pitting, I'd probably blast it enough to get all the 'stuff' out (protecting the seal recess), then lightly hone it to restore the smoothness.

[WMarshy]

Has anyone cleaned up the caliper bore or piston with media blasting (i.e. glass bead)? I am wondering if this would be a viable cleaning option.

MP

The caliper body is aluminum so I wouldnt expect it to have the amount/type of corrosion carbon steel develops (like the piston). As mentioned in previous posts above, although the bore of the caliper body is a nice machined surface its not a critical dimension that needs as tight tolerance as the piston, it acts as a guide not a sealing surface. I wouldnt hesitate to use some 150 grit emery cloth on the caliper bore to remove any corrosion/junk from its bore. Dont go crazy because you dont want to change it dimensionally. Also, you want a nice sharp shoulder on that o-ring grove so keep that in mind while cleaning these up. By doing media blasting you stand a good chance of dulling that sharp shoulder for the o-ring... Just to clarify, if that shoulder gets rounded off or chamfered the o-ring can roll and cause the piston to stick, it could cause premature ware and failure of the seal if it has XSive clearance feom that dull shoulder...

[WMarshy]

The piston would be a no-no, as the surface finish on those is designed to be smooth enough to move in the seal, but with enough 'stiction' to grip the seal and retract the piston when the brake is released. Generally, any damage on the sealing surface means the piston should be replaced.

The bore is another question.... This isn't a sealing surface, more like a 'guide' for the piston. As long as the piston can move freely without too much slop, the bore isn't critical. Now, the recess the seal fits into is another matter; I don't think you want to damage that area at all.

If you found a bore with heavy corrosion/pitting, I'd probably blast it enough to get all the 'stuff' out (protecting the seal recess), then lightly hone it to restore the smoothness.

If you're replacing the o-ring in the rebuild I would recommend leaving the old o-ring in the groove during the media blasting. This allows you to get the blast 90% of the junk out and ut also protects the shoulders of that o-ring groove. You'll still have to go in and clean that groove by hand though...

[Orange4]

By far the easiest way to get the piston out is to unbolt it, leave it attached to the brake lines, open the reservoir and top it up as you pump the piston out with the brake lever. Keep the piston pointing up so when it comes free the fluid stays in the caliper. Pour it out into a jar you readied before hand and you are done.

To do the second one just remove the brake line from the first caliper and close the banjo with a clamp and some gasket material or the right size bolt/washer combo. Rinse and repeat.

If it's really jammed then get it moving using a c clamp and some wood blocks.

No fuss, no muss, no grease, no special tools or explosives needed. No fun, I know.