Changing Front Brake Master - problems getting fluid pushed

[Ductard]

I just changed my front brake MC out for a used one. I'm having some problems getting it to pump fluid and I was wondering what else I can try. Details below, along with anything I think I might have screwed up along the way.

I took the master off ~2 weeks ago. I didn't have one of those little plastic screw-in plugs so I got all the fluid out of the master with the expectation of putting it back in within a few days. the MC and the Caliper were both "Dry". I knew that getting a dry brake system re-started is supposed to be a PITA (set aside whether that makes me more or less of a dumbass for going ahead anyways), but I have a mityvac and I was planning on doing a back-flush as I've seen elsewhere on these forums.

I don't suppose any of the seals would have dried out or anything bad like that in the course of 2 weeks?

So I hooked up the mity-vac, and after figuring out how to get a good seal, I started at the caliper (probably a mistake) and vac'ed away (up to 25) and got ~20cc's of brake fluid out but no more.

I stepped up to the handle, topped off the reservoir and confidently (read: arrogantly) squeezed the lever expecting it to firm up after a couple of squeezes. Nothing.

I wondered if the cheap chinese lever I bought maybe wasn't letting the plunger go out far enough to open up the system to the reservoir so I took it off and put the (bent) OEM lever back on. I had had to file it to get it to fit in the perch, so obviously the idea of "tolerances" are lost on the manufacturer. Still nothing. Took it off and started playing around with the push rod that sticks out of the dust boot and the whole thing just came right out. After half a second of panic, I realized that it was rounded at the end and couldn't be the piston, so I popped it back in.

The MC is used, but I think it worked (I watched the guy take it off of the full system that he wanted to sell me) but it wasn't on the bike and I didn't think to ask him to let me try a few squeezes before he took off the banjo.

Is it possible that I just sucked the piston in so far with the mityvac (I went all the way to 25lbs) that it can't pop back out?

So there's where the clock stuck 1am and I had to call it a night - thought about it later and could it be as simple as cracking the banjo and letting the piston pop back out?

Either way, I'm planning to buy a big syringe from CVS and trying a back-flush today - maybe even trying to pump fluid straight through the banjo bolt hole to pop the piston back out (if compressed air is the quick fix here, I don't have any so I'd have to pick something up).

Any thoughts before I spend a significant amount of time piddling around with this?

[TrackRat]

Jeff,
You should be able to use the master cylinder, itself to pressurize the piston, and push it out the bore. Keep fresh fluid in the reservoir, and just pump the hell out of the handle, until you stop seeing air bubbles come into the reservoir. Syringe is a good plan, too. I've never been a big fan of vacuum pumps for brake bleeding. I use a motive pressure bleeder on my cars, and I'd love to find adapters, so I could use it on the motorcycles.

-Jon

[CBR929RE]

if it has a remote reservoir just squeeze the tube till bubbles stop coming out. fills your master and your lines at the same time.

[Ductard]

if it has a remote reservoir just squeeze the tube till bubbles stop coming out. fills your master and your lines at the same time.

The problem is the piston seems to be lodged closed so it would be blocking the path to the reservoir. I'm going to try to force it out with a syringe (pressure bleed)

[Eric Baker]

Did you bleed the master? What kind of master is it? If it's an OEM unit, crack the banjo and pump until you get steady fluid leaking from between the washers, then re-tighten. If it's an aftermarket unit, it likely has a bleeder screw on it for this purpose. If there's air locked in the master, you'll pretty much never be able to bleed it further down to the caliper. Also, even if the caliper piston is bottomed out, fluid can still get past from the banjo bolt to the bleeder.

[Ductard]

Uhhh..so....I finally went native on this thing. Took the lever and dust boot off of the MC and I can't even move the piston by yanking on it with a pair of pliers. I think it's toast. Not sure how it seized like that with fluid in it but no telling how long it was in that dude's basement.