Front Disk Brake Won't Fully Release

pippend650 · Full Member Joined: Aug 27, 2009 Posts: 10

I noticed the other day that something was really dragging me down and after lifting the bike off the ground, found that the front disc brake is partially engaged. There seems to be fluid in the reservoir and the cable is working. The lever releases fine. About the only thing different is the temperature has dropped about 20-30 degrees. Any thoughts?

Visegrippe · Full Member Joined: Sep 03, 2009 Posts: 10

could be the piston is sticking, aluminum contracts faster than steel, so that what was clearing before is interference fit now...

jayel

the master cylinder resevoir has two small holes in the bottom of the cup one the about a 1/8" you can see and a smaller one hidden under the plastic tab of the cup if it gets plugged the excess fluid can't bleed back causing the calipher to stick, you need to clean your brake system and put in new brake fluid, pumping a couple refills of brake fluid thru it might clean it out but if it still sticks it's very dangerous could cause front wheel lock-up

xsleo

If there is any moisture in your fluid it can settle in the caliper. At those temps it could be freezing. As jayel said , changing the fluid is a good idea. I change mine every couple years. This helps keep everything clean.

pumps

Besides flushing out the system with new fluid it might not hurt to pull that caliper off and apart. See what the seals and piston conditions are. Mine seemed to work fine but after taking it apart for inspection it wasn't so great after all.Probably original 1977 stuff. Lots of crud and rust. I put a Brake Caliper Rebuild Kit ($19) , Rubber caliper sleeve Boot($9), Caliper Piston ( $24), Brake Pad Set ($15) . Shot some brake parts cleaner through it and gave it a coat of black rustoleum and it was as good as new. Oh and new brake braided brake lines. New master cylinder as it was only $10 more for a new one that to rebuild and still needed a new reservoir.
Seems like I spent some $$ I know but good brakes can save your a$$. Oh and when using the blow gun from the compressor to push the piston out of the bore be sure to keep your finger out of the way.

blackwidow

Yeah I had one do that I endind up bleeding it and it's been fine so far.

pippend650 · Full Member Joined: Aug 27, 2009 Posts: 10

I looked into it and found no blocks in the holes in the master reservoir. Next went down on the caliper and eventually found the piston to be really clogged with crud under the rubber part that seals over it. I think it is sticking. The pads were fine. I'm tempted to just get the whole new caliper from Mikes rather than mess around with it. What do you guys think? I wonder if the caliper where the piston moves in is corroded and then you just have more problems again if it is not all just replaced with new. Again...thanks for everyone's help.

gordo · Last edited by gordo on October 29, 2009, 4:56 pm; edited 1 time in total

Brake's are nothing to f### with. It is not rocket science, but if you've never done any kind of brake work, replacement is probably your easiest option. Having said that, a new piston & rebuild kit from Mike's is allot cheaper then a whole caliper. Generally, the bore in which the caliper sits is ok, the piston's get all the corrosion.And being the bike's are 25 + year's old, rebuilding is a must do. In the manual, it gives pretty clear instruction's on how to do the rebuild. Plus the satisfaction of doing it yourself.Just remember that brake fluid WILL remove any paint it comes in contact with. Just flush with water as soon as possible, to minimize any damage.There are a couple of way's to remove the piston without getting hurt from a flying piston. First is use the master cylinder, just pump the handle with the caliper off the mount's & pad's removed. Might have to refill the reservoir to get the piston all the way out. Another is to use a greasegun with a metric fitting in the hole where the brake line attaches. Anyhow, Good luck on whatever you decide, we're allways here. Smile

PS, the braided steel line's are top notch,& cheeper than the rubber line's. They eliminate all the spongyness associated with rubber line's.

acbanks

It's my understanding the the caliper piston rings are actually responsible for retracting the piston.

gordo

Bank's, that's true. But it's not ring's per say. The bore has a taper to it where the seal fit's, & that's what retract's the piston slightly.

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