Binding brakes!

[mikey_m]

Right, ive got an MOT this up coming saturday and ive got a funny feeling that its not going to pass due to the front brakes binding ( rubbing ).

Now ive took the pads out, pushed the pistons back in, and re-bled. But they still manage to rub, only slightly though. I can hear them rubbing. although its hardly noticable. Do you guys think this will pas an MOT like it is? i have no idea how to sort this kind of problem :smt013

Also, the discs arent warped. are these type of brakes supposed to *almost touch the disc*? Sorry for sounding so thick.

Thanks alot, michael.

[extonyg]

they would have to be binding heavily to fail an mot, does the wheel spin freely enough?do you put grease on the pads and pins when you took them out?if the bike has been sat for a while sometimes they just need a bit of use.
and the pads are supose to sit very close almost touching the disc but not quite.if you squeeze the lever you should be able to watch the pads move out and retract back slightly, if they dont retract could mean the pistons in the calipers req removing new seals and cleaning as they can corrode and get dirt behind the 'dust' seal.

[mikey_m]

ive already gave the pistons an overhaul. so theyre clean as a whistle. The wheel spins, but doesnt free wheel, its stops like 2 thirds of a full cycle of the wheel. So im not sure. and yes i can just make out that the pads are retracting but i cant see any room between the pads and disc :smt013

[cargo]

Just cleaning the pistons is not enough the seals play a part in retracting the pistons once you release the lever.

As extonyg says corrosion and build up in the seal groove and cause the piston to stick.....................the only way to clean the groove is to remove the piston and the seal and clean the groove I've found a wire brush fitting for a dremmel is excellent for this......................it is possible to do this job and reuse the seal bit it will need to be handled carefully and cleaned as well

[mikey_m]

The pistons retract fine! Its just they are keeping the pad really close to the disc so its causing it to rub slightly. if i squeeze the front brake, they work fine as they should.

Do anyone know what the legal limit is regarding the lip around the disc? like the groove on the outside of the disc. mines getting pretty bad.

Cheers

[parby81]

use a vernier caliper and read the minimum thickness on the disc, its stamped on it

[extonyg]

discs with a big 'lip' on them could be part of the reason that the brakes are binding slightly as the pads sits inside the groove or lip rather than just the outside.
also if your discs are that worn they could fail the mot for being to thin or also brake imbalance.

[mikey_m]

i dont think they are too thin. As last time i took my bike for an mot a few months ago, it only failed on fork seals and rear brake pads. which both have no been replaced

Just out of interest, can you grind down that *lip* on the outside of the disc??

[extonyg]

yes technically you can...........but this doesnt stop the disc being at its minimum thickness just means its even wear without the lip.
everything has to wear out one day and maybe just one day your front brake might just save your life.....i think if the discs are at there minimum service limit then they need changing personally.but yes i do no of people that grind the lip off there discs and there fine.