brake piston reinstall

[alorio1]

I have removed and cleaned front brake caliper pistons because of pads dragging a bit on rotors. I still have one caliper that drags more than I would like it to. I used brake fluid as lubricant to reinstall pistons, I am wandering if I use some silicone gel type lubricant on this one piston thats not returning like the other 3 will I have problems with seals swelling or any other side effects.

 

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I've heard horror stories about mixing a convention DOT 3 or 4, glycol based fluid with a DOT 5 silicone based fluid. Not sure if a silicone lube would produce the same effect? :confused2:

I wouldn't bother with the silicone lube. I don't see it taking care of your issue. If everything is in good shape a conventional DOT3 or DOT4 fluid should provide enough lubricity. I would disassemble again and make sure the pistons are clean and polished thoroughly, the piston and dust seals are in good condition and not hardened, and the bore of the caliper is clean and smooth as well.

 

[wlodek1980]

i wouldn't put anything other than brake fluid inside the brake system.

 

[alorio1]

I found my problem, I was using a monster C-clamp and didn't realize the piston was going back in crooked. When I disassembled it I could see I had sheared off a piece of the seal itself from piston not being square with bore. I replaced seal and outer dust seal and pressed piston in with my thumbs. So, it's good to go now with front wheel spinning with a slight resistance like it should be.

 

[Fire-medic]

Yes, my suggestion would have been to discard the seal & dust boot and replace w/new. They work in a tough environment, and between ozone, UV light, heat/cool cycles, they deserve to be replaced.

The only time I have used a c-clamp is pushing-in pistons when I haven't removed & disassembled them.

Repeating an older post, if compressed air won't budge the pistons, I still recommend the use of a grease gun, just put a correct-size bolt into the brake line caliper hole to block it off, and use the brake bleeder to fill the caliper w/grease. It has worked every time for me if I encounter a stubborn piston. Just remember you may have to use a block of wood or two to hold the other pistons stationary, this is one place where a c-clamp to hold the opposed piston stationary may work well.

If you have the check-valve brake bleeders, do not forget to replace them with a standard open type. If you really wanted to bring the maximum hydraulics to bear, cut the end off a brake bleeder so you get the max. bore size to flow grease thru the innermost-dwelling portion of the brake bleeder.

 

[94 V-Max Rider]

I have removed and cleaned front brake caliper pistons because of pads dragging a bit on rotors. I still have one caliper that drags more than I would like it to. I used brake fluid as lubricant to reinstall pistons, I am wandering if I use some silicone gel type lubricant on this one piston thats not returning like the other 3 will I have problems with seals swelling or any other side effects.

Some (slight) drag is perfectly normal, but now that you went and removed the pistons, you should replace the seals after cleaning out all of the corrosion in the grooves where they sit, which is usually what causes brake pistons to hang up.

Also, inspect the pistons. If there's any nicks or pitting in the line of seal travel, they should be replaced. I wouldn't lubricate the seals and pistons with anything but DOT 3-4 brake fluid. While you're at it, it wouldn't hurt to replace the pad springs.

On the plus side, you'll have a set of completely rebuilt calipers.