Rear Brake Issues

[Cdelisle95]

Hey guys,

I have been fixing up a 1979 xs400 on and off for the past year. The bike sat for about a month, and when I took it out for the first time, the back brake does not function at all. (This is a dual disc brake bike.) When I went to bleed the brakes in hopes of fixing the issue, pumping the pedal moved absolutely no brake fluid out through the bleeder screw. I am kind of at a loss for what to do. I took apart and rebuilt the caliper, and everything looks good. Line looks fine. Could there be an issue in my rear master cylinder? Any help would be greatly appreciated.

 

[kshansen]

Sounds like time to do the master cylinder next.

 

[Cdelisle95]

Sounds like time to do the master cylinder next.

Do you, or anyone else around here, have a lead on rebuild kits for the rear master? I see front master rebuild kits all over but not much for the rear. Would the two be interchangeable?

 

[Sesty]

nearly impossible to find rear MC kit at least it was for me. There are caliper kits and pistons available.. took the MC apart and cleaned all parts and passages thoroughly w a fine wire, new brake line and have not had any issues with the caliper dragging and locking up once heated up. At least for me, the very small return passage was blocked due to age and likely rotting brake lines.

be sure to clean any fluid off any panted surfaces... my caliper will need some paint this winter

 

[Old Mose]

Some times master cylinders will loose their seal when they are of advanced age and sit for a while. You can use a brake bleeder syringe full of fluid on the caliper screw to force pressure into the system while working the pedal at the same time. It may or may not work. You don't have anything to loose.

 

[Cdelisle95]

Thanks for the advice everyone, I should have time to dive back into it this weekend. If I figure it out I'll post an update with what the solution ended up being.

 

[Old Mose]

Did you have any luck with the rear master cylinder?

 

[Cdelisle95]

Did you have any luck with the rear master cylinder?

I did! Life got in the way and it has been a few weeks since I'd had the time to mess with it at all.

I took the whole rear master off and soaked it in PB blast for almost 36 hours, which managed to free up the cylinder to at least let it move a little bit. Then I disassembled essentially the entire cylinder and cleaned each part individually, did some wet sanding, put it back together and it works fine after bleeding the brakes. Not nearly as complicated as I had originally thought, but you do need a pair or circlip pliers. If anyone happens to read this and has questions feel free to ask, this is a very doable job with a little patience. No rebuild kit needed.