rear brake issues

[mikromo]

I bought a 2010 Ninja 250 a couple of weeks ago, largely because a local dealer tried to rip off the PO. She rode it to the dealer with rear brake issues (pads worn slick). Once there they REMOVED the rear master cylinder and refused to let her ride it home. So, when I bought it the rear master cylinder was in a bag, and the rear brake completely inoperable. So last week I got new pads, and yesterday I installed them and attemped, with a mighty Vac, tried to bleed new dot 4 through the system. I can't get any brake fluid to bleed through. Now I have bled many brakes over the years, but this one has me flumoxed. I even took off the brake line from the top of the MC and can see fluid, but no amount of manipulating the rear brake pedal even causes fluid to pump out. Is there a bench bleed procedure for the MC?? My Mighty vac will hold 25psi vacummn all day long, with no brake fluid leaving the resevior. I'm thinking of buying a syringe and trying to "back bleed" it (thought I had one but no where to be found). Any advice? Please.

[Motofool]

Originally Posted by mikromo

............My Mighty vac will hold 25psi vacummn all day long, with no brake fluid leaving the resevior.................

It seems that the whole problem is in the master cylinder.
It should freely pump down the hose from the reservoir.

I think you meant 25 inches of mercury, since 14.7 psi is the maximum achievable vacuum.

[cuong-nutz]

Originally Posted by Motofool

It seems that the whole problem is in the master cylinder.

+1

[Lychee]

I would replace the master cylinder. You could also rebuild it if cost is an issue, but replacement is better. It sounds like the piston is stuck inside.

As a side note, from the info given, it doesn't sound like the dealer was ripping the PO off at all. It sounds like she didn't want to pay for a rear master cylinder replacement, which you have discovered is actually necessary. Although the dealer should have returned her key when she asked for it and paid the bill. I don't think refusing is within their rights while advising against would be. You probably got a smashing good deal on the bike though.

[JAG]

Put pressure on the plungers to get them started. No fluid coming
Out of open bleed screw when brake applied not sure the problem

[mikromo]

Taking it apart tommorow (the m/c) I'll clean the bejesus out of it, pre load the lines, caliper, and m/c, and try again. I'm thinking sploog in the return hole. But if not....it's a new one. The reason I think the shop was trying to rip off the PO, is they wanted to sell her a m/c, a new caliper, a new disc, + pads. The disc is within spec, The pistons in the caliper move freely...... they were quoting her near $700.00. Rip off in my book.

[mikromo]

Couldn't wait for today, so last night after dinner I went into my workshop and got busy. It was a stuck piston in the M/C. There was quite a bit of corrosion around the snap ring and washer that holds it together, and the part of the rod that touches the "business end" of the piston looked kinda rusty, fluid probably had never been changed, so at some point it absorbed some water. Upon inspection the seals looked brand new, so I carefully cleaned everything, worked on the "piston" with 1500 grit sandpaper, cleaned up the cylindr bore with fine steel wool (no hone that small) lubed everything with dot4 and reassembled. WALA! Rear brakes (not that I missed them). Should be even more fun to ride now, knowing that all is right, and I can see some brake sliding may be in my future, as I'm an old dirtbike racer. Saved me $178.00 (Ron Ayers) for a new one, so, so far I've got $32.00 in repairs in my $900.00 special, spent on EBC pads. Thanks for all of the helpful comments!!

[Alex]

nice work.