Bleeding Rear Brakes

GMP

GMP

Active member
OK guys. time to help me out if you can. '07 EC250 with Nissin integrated resevoir rear master cyl. I cannot seem to get this thing bled. Right now I'm thinking I may have a bad piston cup seal and will take it down tonight and check. Before I do, are there any tricks I'm missing? I've done countless Brembos and other Nissins but none as a PIA as this. I've put a lot of fluid through it backwards, backwards while cycling the piston, and drawing it back through the caliper. No bubbles evident by any method but obviously there is big air in there somewhere.
 
My trick is to use bubbles to find the problem.

Take the brake caliper,master cylinder off as a unit, teflon tape the bleeder, submerge the whole thing, then pressurize with air. If you've got a leak, you'll find it.

Is the reservoir cap vented? (i've got an old 2002 with the cap off). You may need to block that.

I had a friend with an Italjet scooter, with AJP brakes. (Try finding parts for that thing.) Anyway, we had brake issues, and it turned out that the cup seal on the master cylinder piston had swelled, and the ID of the cup seal was bigger than it should have been. Weird. Anyway, i ended up making an ever so thin spacer and it would then seal the ID. It held pressure, and we were able to bleed successfully. it took me HOURS to chase that down.

I hope this helps. Good luck.

blitz
 
Glen, my 07 took 1/2 quart of fluid through it to get it right. I am not a big fan of the integrated resevoir, though I never liked the position on the tube to the resevoir on my 02 either. I guess its a pick your poison sort of deal.
 
Paul,

So you had trouble too I assume. I'm going to take the system off the bike tonight and try it with the master cyl in different positions.

blitz,

My wife's Pampera has AJP brakes. I totally smoked the rear caliper, burned everything up and melted the o-rings. Trials brakes not made for aggressive use. Rising Sun had everything I needed to rebuild the caliper and master cyl.
 
Glen, I did it about a year ago and I remember it being about a three beer job. I sucked air into the system right away not realizing how little that resevoir holds and then it took way longer than it should.
 
I had to do this this summer after the cup in the master cylinder cracked going down a hill. I don't remember it being too bad of a job, just have to make sure you don't let the fluid level in the master drop while you are bleeding it. You can also pull the caliper and hold it above the master so that all the air rises to the caliper and out the bleed screw. A side note too, just about all the late model 250 2-stroke mx bikes used this rear master, so parts are easy to find. I think I used a RM250 rebuild kit in mine.
 
OK guys here is the trick that worked: First, I re-taped the bleeder threads for a real tight fit (thanks for the reminder blitz), and pushed on the caliper to purge the small amount of air from the nipple. Put my 50cc syringe on, pulled back REAL HARD and cracked the nipple. Just fluid. Keeping the master cyl topped off, did it again, now a big slug of air followed by small bubbles and then clear fluid. All is well now.

You could back bleed this thing with a quart of fluid and get nowhere, the air remains trapped. Its the high vacuum / high velocity of fluid in the normal direction that did it. The air was trapped in the master, but had to be pulled through the line and the caliper to get it out.
 
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