Hi everyone i wondered if you could help me i have just had a look at the front brakes in the race bike as i am giving every think a once over before i get my engine put back together and go testing on it, i pumped on the brake lever to find in the left hand caliper the 1 piston was stuck right in :S and in the other caliper the two pistons look a little lazy. Ive stripped the calipers to find they are relatively clean inside and all the holes inside are clear, it only had new seals about a yr ago now so what could be causing the pistons to stick ? Your help would be greatly appreciated as the brakes on this bike have been an absolutely god for saken nightmare

Are the pistons scored in any way ???
I guess you've used some red rubber grease to lube them ???

Is there any corrosion where the seals fit, that would mean the seals are tighter than they need to be. Were the seals genuine or pattern parts, they could be a fractionally different size causing the pistons to drag

Evilchicken0 wrote:Are the pistons scored in any way ???
I guess you've used some red rubber grease to lube them ???

Is there any corrosion where the seals fit, that would mean the seals are tighter than they need to be. Were the seals genuine or pattern parts, they could be a fractionally different size causing the pistons to drag

No they don't appear to have any scores on them and yes i use red grease i have put it all round the seals is that correct ? and what would happen if there was no red grease would that cause them to stick ? and there is absolutely no corrosion what so ever and the seals were genuine Yamaha ones

There's no reason that I can think of that would mean they'd bind then.
Could there be any problem with the master cylinder ???

Evilchicken0 wrote:There's no reason that I can think of that would mean they'd bind then.
Could there be any problem with the master cylinder ???

The master cylinder again was only rebuild using genuine yam spares i said it was a complete mystery

yes ... you've got me on that one.

Any chance you can swap stuff out to see if it's just the calipers ?

Evilchicken0 wrote:yes ... you've got me on that one.

Any chance you can swap stuff out to see if it's just the calipers ?

What sort of stuff do you think i should change ? master cylinder ? because i think that's the only thing i haven't changed even though the one on there has been rebuild. Ive just taken the calipers apart and polished all the pistons back up and re greased them with red grease and under compressed air they seem to work fine but that's a lot more pressure than a master cylinder can put out i guess. If that don't work have you got any more ideas ? Im fed up with these brakes Ive tried everything and nothings working

I guess I'd swap the master cylinder. But if you know somebody with good brakes then swap the bits out and hopefully at some point you'll find the bit that doesn't work. Start with the master cylinder .... any master will do. I've even used the rear master to test a caliper.

I would try the dodgy piston in the other caliper and see if that makes any difference .

you could also lose the dust seals ....but you would have to clean them a bit more often.

levo wrote:I would try the dodgy piston in the other caliper and see if that makes any difference .

you could also lose the dust seals ....but you would have to clean them a bit more often.

The dust seals are out because i was told before they tend to grab the pistons a little bit more than without. Im trying to bleed them again at the moment after stripping them all down polishing the pistons up and testing them under compressed air, i know it a false way to try them under air but it gives me a little reassurance that i am not wasting my time when i put them on properly. At the moment they are being soo crap to bleed its horrendous, all the pistons have come out but only slightly and they is absolutely no pressure what so ever there, odiously because the pads are not touching the pads. I haven't finished bleeding them yet tho its been through about 3 reservoirs full of fluid. Could there be a problem with the master cylinder after all ??? Thank you evil chickens as you mention in the above post it sounds a great idea but i don't really want to take the rear master cylinder off and disturb it as i have no problems with that