Sticking brake piston

[Premature Accelerato]

I have 4 pot caliper with a sticking piston. I can spin the front wheel but you can hear it rubbing and the rotation is not as free/fast as I believe it should be. The pads are wearing faster under this particular piston than the others. I have replaced all the seals and meticulously cleaned everything and put it back together. It still did not retract as much as the other pots (you can see it moving back, just not as much as the other 3). I pulled it all apart again. Measured the pistons, all measure the same and then replaced them in different positions to see if it made any difference. It didn't. Pulled the whole lot apart again in case I missed something like a speck of dirt but nothing. Anyone have a suggestion, am thinking the rebate that houses the seal may be a thou or 2 shallower than the others.

[AllanB]

What's the bike, year and brake (brand).

Too much drag is never nice

[Premature Accelerato]

Tokico, 2007 GSXR 750

[FJRider]

Have you checked to see if the disc is true ... ??

[husaberg]

A warped disc kicks away the pads, His appears to be constantly dragging only on one pad. if it warping it will only drag in one position.
Sorry i suggest taking the caliper apart again and degunking it.
If one piston doesn't retract fully its normally surrounded with crud that prevents it going back.
Is the piston itself free of nicks etc? the caliper itself?

[Premature Accelerato]

The discs are running true, no problem there. I pulled the whole thing apart after work ,cleaned out the seals and grooves again but no improvement. Its doing my head in.

[AllanB]

Have you checked the piston is round with a accurate caliper?

[Premature Accelerato]

No, I havnt checked for round but I have put each of the other pistons into the same pot and they all do the same thing. Am thinking I need to find a way to measure the I.D of the seal groove to see if it is smaller than the other pots of the same size.

[FJRider]

Beg / borrow / steal ... another set of calipers and see if there is improvement ...

[FJRider]

No, I havnt checked for round but I have put each of the other pistons into the same pot and they all do the same thing. Am thinking I need to find a way to measure the I.D of the seal groove to see if it is smaller than the other pots of the same size.

Is there enough meat on the disc to reface it/them ... without going under minimum disc thickness ... ??

[jellywrestler]

No, I havnt checked for round but I have put each of the other pistons into the same pot and they all do the same thing. Am thinking I need to find a way to measure the I.D of the seal groove to see if it is smaller than the other pots of the same size.

how did you clean out the groove?

[Grumph]

If the same caliper bore is the problem with different pistons, I'd look at the bore.
It's easy enough to mark the bore putting pistons in dry or crooked.

Edit - Pull the seal and see how free the piston is in the bore. Might have to get a pro to give it a light hone.

[jellywrestler]

cleaning out the groove it the had bit, i use a dentists hook tool to get right to the edges and ensure there's no crytalised bits in there, that's the worst area and will put extra pressure on the seal

[Premature Accelerato]

cleaning out the groove it the had bit, i use a dentists hook tool to get right to the edges and ensure there's no crytalised bits in there, that's the worst area and will put extra pressure on the seal

Cleaned it with the curved end of my trusty old scrubber. I have just pulled it apart again and put the piston in the pot without any seals. It slides in and our easily. I then put the oil seal in by itself and the piston works the same as the others. I then put the dust seal in and the bloody things tightens up to buggery. So I would guess that perhaps the seal is slightly too big or the seal is a little over size. All the extra cleaning at least gets me a 1 1\2 turn of the wheel when I give it a spin. Enough ya reckon?

[jellywrestler]

Cleaned it with the curved end of my trusty old scrubber. I have just pulled it apart again and put the piston in the pot without any seals. It slides in and our easily. I then put the oil seal in by itself and the piston works the same as the others. I then put the dust seal in and the bloody things tightens up to buggery. So I would guess that perhaps the seal is slightly too big or the seal is a little over size. All the extra cleaning at least gets me a 1 1\2 turn of the wheel when I give it a spin. Enough ya reckon?

so if you suspect the seal a differnt size measure it with a vernia
or why not put that seal in another hole and try and chase the fault,
a curved end of a trusty old scrubber, sounds like a dildo of a chick i knew in featherston, commonly known as metahamfeatherston.
seriuosly what is that tool? as said i use a hooked dentist tool, lightly but you can feel the shit and feel it dissapear

[Premature Accelerato]

Sorry, a typo. Meant to be scribber. Its probably a bit heavier than a dentists tool but was used gentlly and didn't scratch the hell out of the casting. Their was a little bit of crap there, not a huge amount. Guess I will have to pull the other caliper apart to get a good comparison.

[Grumph]

Cleaned it with the curved end of my trusty old scrubber. I have just pulled it apart again and put the piston in the pot without any seals. It slides in and our easily. I then put the oil seal in by itself and the piston works the same as the others. I then put the dust seal in and the bloody things tightens up to buggery. So I would guess that perhaps the seal is slightly too big or the seal is a little over size. All the extra cleaning at least gets me a 1 1\2 turn of the wheel when I give it a spin. Enough ya reckon?

Surely you mean the dust seal is Undersize. Are you putting any rubbergrease on the OD of the piston or the ID of the seals ?
Turning the dust seal inside out can often reveal accumulated crud.
Bit like inspecting the ID of Methamfeatherston I suspect....

[Premature Accelerato]

By over size I mean it is too tight but I guess you could call it undersized. I have put a small smear of grease I got from Boyles a couple of years ago, to lubricate things. I have used the same grease many times on brake seals and it has never given me any problems. It is red in colour but I cant remember its brand/trade name. I'll get there in the end.

[jellywrestler]

Surely you mean the dust seal is Undersize. Are you putting any rubbergrease on the OD of the piston or the ID of the seals ?
Turning the dust seal inside out can often reveal accumulated crud.
Bit like inspecting the ID of Methamfeatherston I suspect....

i snuck up the hill a wee while ago and altered their sign.....
take a good look at the little square boxes too.

[jellywrestler]

so did you just replace one seal?
did you clean the grooves out thouroughly, ie with a solid scraper to pick the shit out of it,
if you move the seal to another hole them if the issue follows it there it's the seal,

[Voltaire]

Its unlikely but if the compensation port ( very small hole)in the master cylinder is partially covered by the piston seal pressure builds up and pads drag. can be caused by sticking brake lever/actuation mechanism.

[Premature Accelerato]

I have now cleaned the absolute shit out of these calipers. I measured the dust seals and the offending seal was actually 0.2mm thicker than the nearest sized seal. I have put that seal in a different pot with the smallest dia piston (albiet by only 0.02mm). Although the amounts are not much, surprisingly the wheel now spins quite freely.

[jellywrestler]

I have now cleaned the absolute shit out of these calipers. I measured the dust seals and the offending seal was actually 0.2mm thicker than the nearest sized seal. I have put that seal in a different pot with the smallest dia piston (albiet by only 0.02mm). Although the amounts are not much, surprisingly the wheel now spins quite freely.

yah that's 5 thou, for the seal, usually it's lumps in the grooves that can't be easily seen that cause the issue., well done

[Scubbo]

time to upgrade to nissin calipers :shifty: --- glad to hear its sorta-sorted ...