Rear Brake Master Cyl.

[Faded]

Trying to help out a friend with his '87 RM250 here. We bleed the rear brakes because they were starting to fade really bad. After that we couldn't hardly get any pressure. We made sure there wasn't any air in the lines and it still didn't work. He took it off and had the seals replaced (dealer) and it still didn't work. After talking with the dealer he said that (if he remembers correctly) there was a small groove in the body. Can this be fixed? I haven't had it apart myself, but if someone was willing to help walk me through a dissassembly I'd be more than willing to take it apart and provide photos. Thanks in advance, any and all help is appreciated.

 

[Joepro9]

have you checked the obvious stuff first? My brakes started to fade because my pads were shot and I did not even know it. Also what shape is the rotor in? Its not glazed in oil or anything? I had a buddy try to lube his breaks one time, just glad he did not go jumping after words..... What kind of "groove" exactly are we talking?

 

[Faded]

Pads are about 50%, no uneven wear to speak of. Rotor is still good and within spec, no glaze to speak of. There hardly is any pressure to speak of at the caliper. Working from second hand info (sorry, but it's all I got right now) the 'groove' the dealer was telling my buddy about is the the master cyl body. If I understand it right there is a pushrod that forces the fluid through the m/c body. This push rod has a seal on the end, and I guess the seal was so far worn, or there was a foreign object in there that wore a groove into the inside of the m/c body which would allow fluid past the seal and explain why you can't build pressure. Any thoughts?

 

[Faded]

Dup. sorry.

 

[Joepro9]

sounds like its to visit the junk yard. Or just get a new one, brakes are nothing to fool around with. I cant think of anyway to fix the grove unless you put a patch of weld or sothing into it. I wouls just not feel safe riding around on brakes that are "half-assed" in terms of working or fixed.

 

[Faded]

I agree, but I am still hoping to get some other opinions. I don't know if you can have it honed or somethings similiar.

 

[Zerotact]

If the part is already shot, and the groove is shallow, a hone might get you by, but you can't hone the housing out beyond the size to the seals...

Back in the days of drum brakes, you could hone out the slave cylinder, and slap new seals on, and you were good to go.

 

[Faded]

I guess I better take it apart and see for myself then. Ever had one of these apart?