Rear caliper is sticky.

[James Sea]

Hello everyone, my name is James. I recently purchased a 1978 XS400, with 5600 miles or there abouts, off of Craigslist. It runs and shifts pretty well but the rear disc caliper is acting funky. I pulled the caliper off and cleaned it as much as I could without actually pulling the piston out. There was some rust on it that came right off. I also changed the brake fluid and made sure to get all the air out of the lines.

The symptom is the the piston inside the caliper does not seem to want to return fully after the brake pedal is pressed down, causing it to drag on the rear disc. If I hit the outside of the caliper with my hand it resets it enough so that it releases. If anyone has any ideas on how to fix this I would really appreciate it, hopefully not buying a new caliper.

 

[James Sea]

 

[Sesty]

There is probably a clog in the master cylinder. I had the same problem, Drained fluid, took off MC and took it apart cleaning everything as much as i could. There is a very small hole which is how the fluid returns back to the MC. Rear MC kits are hard to find so i couldn't replace any of the bits.

Mine was blocked solid with crud (Rust, Crystallized fluid). Poked it clean with a guitar string and lots of compressed air.

Some people have success with just pushing the piston back in with a c-clamp which forces the hole clean. This is method is just a band-aid on a broken arm tho as it will likely clog again.

there are a few threads already on this topic.

 

[drewpy]

James, you can't code from your PC for pictures. it will work for you but not for us. Use a photofucket account

 

[XSLeo]

If you hit the Go Advanced button below where you write, scroll down to the manage attachments button, browse then find the pic on your computer, upload and the pics show up.
Leo

 

[James Sea]

http://i1167.photobucket.com/albums/q624/jachuff2/002_zpsy8sdlyph.jpg

Alright, been kinda busy that's why the slow response. I took your advice Sesty, and now the rear brakes works really well. I don't think that the master cylinder had been apart since the 70's. Been riding out these last couple days and it has been good. I have a new issue though that I'm gonna post in the electrical sections and hope that links works.

 

[Sesty]

http://www.ebay.com/itm/76-78-YAMAH...031-/371071039825?hash=item56658eb951&vxp=mtr

just found this on ebay looking for a MC Cap. Its for the XS500 not sure if they used the same MC

 

[iamunique127]

Hey James, your photo doesn't show up for me. I had to click on the link and go to your photobucket. Nice clean looking bike, BTW.

Here's the way I post a photo: look at the line above Message window (either Quick Reply or Reply to Thread), see the yellow square with the mountains and the stamp in the corner? Click on that and paste the address of the photo in the pop-up window that appears. Click OK. See if that works for you.

 

[James Sea]

Thanks Lyle, yeah I will try that in the future. I have a new issue with the bike, electrical, so I'll start a new thread.

 

[sproutroot]

It sounds like your lines might never have been replaced. These degrade over time, and there's a good chance that their degraded bits are making their way down to the caliper and accumulating behind the piston. If that's the case, cleaning the caliper is only a band-aid. This dilemma is always a good excuse to upgrade to SS braided lines.