Front caliper - those creeping pistons

Gutted the front brakes today for full overhaul. Cleaned out master cylinder, including the tiny pressure relief hole. Alot of yellow gunk in there. Put in a new piston kit. All new hoses, and crush washers, thanks Chacal. Blew out the pistons and cleaned out both front calipers, and all new seals, and in with new clean fluid. Cleaned out all the junk from the seal grooves. The bleeder screws were jammed with rusty dirt. Cleaned them out. Most likely because the rubber caps are missing. New ones on the way. My air compressor got plenty of use today. Blew out all passageways clean.

RH caliper went back on fine. When I went to install the LH caliper, both pistons had crept out - even though I had installed them flush. Had to push them back again to fit the new pads. And they started creeping out again. And the caliper is not even connected to the hose yet. Now I'm worried about the caliper possibly dragging.

Have I done something wrong here - like installing the new seals the wrong way around?

 

Did you apply a small amount of caliper (ATE) grease to the new seals and pistons? If you didn't the seals are probably sticking to the piston and that is the reason they keep coming out. Since the system isn't filled yet, try to get hold of some of that grease. (Yamaha packs it standard with a new seal set usually)


grz Thijs

 

Thanks for that. There was a pouch of grease with the overhaul kits, but I just used some new brake fluid on the pistons. Looks like I I'll have to take the pistons out again.

 

Brake fluid doesn't lubricate . Take out the seals and rub them lightly with the grease on all sides. Then lube the bore and piston itself and put them back in. That should solve your problem.


grz Thijs

 

Thanks for that. Dismantled all three calipers again, I have an air compressor to get the pistons out. Put the grease that came with the overhaul kits, on the seals and pistons. Reassembled, and the pistons went into the calipers much easier, and stayed put. Put the brakes back with new pads, and bled with the excellent Mity Vac I got from Chacal.

I now have good working brakes, and no drag on the wheels. The lever and pedal only moves about halfway and is firm.