Hey Guys

I have been having a problem with my front brake recently. Basically it seems to stick on just enough to stop the wheel spinning freely. It seems to be one piston not fully returning.

I order to resolve the problem I have stripped and cleaned the calliper and master cylinder. I have replaced the oil and a full service kit consisting of pistons and seals in the calliper. I have swapped the disc out with another used one. Both are not warped and still within montesa spec.

The only modification with the system is a slim front brake pipe.

I am losing patience with this so any help would be appreciated.

Thanks in advance.

Long shot,reservoir not to full? Piston in master cyl not returning fully or not enough clearance in lever.

Is this happening after riding and hot or whilst on a stand from cold ?

possibly build up of dirt in the caliper seal grooves, which then makes the seal tigher and doesn't let it return when you release the lever.

re-strip it and try to scrape out as much as possible, use a little mirror and you'll be able to see all the dirt in the groove.

also make sure the piston on master cylinder can return fully (adjustment screw not too far in?)

I agree with Chris Morris, but you might find it is aluminium corrosion not dirst. Pacvk some wire wool into the groove and worl it round polish the groove out. I am not familiar with Mont calipers. Seals have a taper on them so that they have a lrger outside diameter at the pad end. Mostly on trials bikes this taper is achieved by the base of the groove not being parallel to the pistion bore but occasional the base of the seal groove is parallel to the bore and the seals are not rectanglar section. If you have tapered seals and put them in wrong way round you get the problems you have.

Cheers