Topic: cb750 front caliper question

[johnyvilla]

I rebuilt my brake caliper a few months ago complete with OEM pucks and seal. I smoothed out the piston bore, cleaned out the seal grove, and slathered the inside with silicone grease. The piston was in decent condition( a few pits) and dropped right in. Once installed the brake had good firm action but bound the wheel ever so slightly. Anyway three months later a stuck puck lead me to disassemble the thing again. Everything looked the same, I cleaned it out, lubed it up, but now the piston must forcefully be pushed in! I used the grease-gun meathod to remove the stuck piston and cleaned the caliper with parts cleaner the best I could. I'm worried now that the seal was contaminated and swelled. Has anyone had this happen to them? thanks for all your help.

[Steve F]

If I were rebuilding the caliper, I would tend to believe that the silicone grease in the brake system would be a bad idea.  I got to thinking about your problem, and was picturing the grease migrating to the brake line and clogging it enough to prevent the fluid from going backward to the master cylinder every time you release the lever.  The fluid has to go somewhere, and with the grease in the line, you essentially created a check valve, which prevents the piston from retracting.  Just a theory, but try cleaning the caliper again and remove all traces of the old fluid and grease, and start over.

[johnyvilla]

I'm not sure if silicone grease got into the return hole, I'm concerned more with the pistons inability to move freely when calipers dry. It should basically drop in and it takes much effort to push it in. It drops right in without the seal but that ddoesn't really help me.

[Bob Wessner]

Your problem could be that the seal has swelled as you suspect. It came in contact with the grease (petro based?) and you didn't specify if you removed the seal before using the parts cleaner. You might need a new seal. This is strictly a guess on my part though.

[snyquist53]

sound like a swollen seal.  no grease next time.  are you using the right brake fluid?  some times that can swell the rubber in a system

[johnyvilla]

I replaced the seal after the cleaning the caliper,but looking again at the silicone grease I'm pretty sure it was was the culprit. It just says SILICONE/GREASE on the front of the tube. I guess I should have payed attention (or drank less) when reassembling my caliper. thanks +