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tsa wrote:I went through this a couple of years ago - in my case the chrome of the ATE caliper pistons was badly pitted in the area where the seal is supposes to, eh, seal. Replacement pistons were necessary, and of course meticulous cleaning and greasing of the caliper seals when reassembling.

In hindsight, dismantling and cleaning the calipers is something that should be done routinely every five years or so, at least if riding on salty winter roads.

tsa, can you recommend a grease? I assume the grease is applied to the seals as well as the pistons? Liberally or lightly?

thanks,

jimmyg

Must not on any account be ordinary grease or any petroleum based product which would swell the seals. The red rubber grease I mentioned earlier is the correct stuff for the job.

If you look at the piston then the portion from the caliper seal inwards is lubricated by the brake fluid so provided the brake fluid is changed regularly that section of the piston doesn't rust. It's the part between the piston seal and the dust seal that is exposed to external corrosion. Even though you'll find pictures on the internet of red rubber grease lathered all over inside the caliper I don't do that but just lightly greasing the whole piston. I don't put any on the inner seal. The place to apply the grease more liberally is the section that needs it between the inner seal and the dust seal.

The worst thing you can do is to coat the whole piston with brake fluid as an assembly lubricant as the part outside of the inner seal will just attract moisture out of the air and rust for sure

jimmyg wrote:tsa, can you recommend a grease? I assume the grease is applied to the seals as well as the pistons? Liberally or lightly?

I will point to Barry's advice wrt grease; find some "red rubber grease". I actually hate generic and/or proprietary names instead of what products actually are, if "rrg" seems to be impossible to find, ask one of your local brake specialist shops. Perhaps other manufactures produce blue brake grease

I concentrated most on greasing the area "outside" the piston seals, under the dust seal, and the contact area between piston & brake pad. I used what I had at hand, a brand specific anti-squeal back-of-brake-pad-grease, which I assume has a VERY high melting point so it doesn't leak out and onto the pads. I tend to use grease sparingly, too much and it may allow dust to stick and greate a grinding paste. Same approach as to the drive splines.

With many previous owners and pad changes, the area covered by the seal of such old caliper pistons have been pushed in and out of the calipers several times, and if any salt/dust/moisture has leaked past the dust seals it may have had plenty of opportunity to start corroding the chrome layer of the pistons. Hence my current approach to take apart and clean old brake calipers (as far as my skills allow me) as a preventing measure.

Good luch with yours, I hope you find them without any significant corrosion!

the right side caliper has one small pit in the caliper piston but that isn't limiting removal.

However, removing the left caliper revealed the issue. The piston is stuck, hard, in the caliper. I have penetrating oil on it now, hoping to free it up in a day or so.

I'll keep y'all updated.

thanks,

jimmyg

I have moved stuck pistons by hooking the calipers up to the brake lines and letting the hydraulic action move it out when I depressed the brake lever. A little messy, but after you remove the brake pads it should have enough room to clear the housing. Keep your fingers out of the middle, cause when it comes out it will pinch them, worse part, it won't release.

jimmyg wrote:the right side caliper has one small pit in the caliper piston but that isn't limiting removal.
However, removing the left caliper revealed the issue. The piston is stuck, hard, in the caliper. I have penetrating oil on it now, hoping to free it up in a day or so.

Compressed air thru the fluid hole?
I had one that moved with some solid whacks against a wooden fence post whilst holding it in my hand, enough for compressed air to push it the rest of the way.

A problem with compressed air is control.
The piston can pop out quickly, violently.
Don't ask how I know....
Pumping it out with the master cylinder and fluid is much safer.

Seth wrote: Pumping it out with the master cylinder and fluid is much safer.

That's what I do every time. If the piston is really stuck it will shift it more effectively than compressed air.

I got the calipers cleaned up and have installed the inner seals.

Are there any tricks to take note of when installing the outer dust seals?

I'm assuming that I place the piston in the bore, press it in a bit and then install the dust seal?

thanks,

jimmyg

jimmyg wrote:
Are there any tricks to take note of when installing the outer dust seals?

I'm assuming that I place the piston in the bore, press it in a bit and then install the dust seal?

Just that although I push the piston in a fair way.