HELP! Newb rear caliper question

[Guest]

OK, rebuilt the rear caliper and rear master cylinder. Trying to bleed the bloody thing
has not yeilded any good results. I have Russel speed bleeders, a Mity Vac and a bit
syringe with a hose. NOTHING has worked so far.

My question... There are two bleeders on the rear caliper. Do you bleed one at a
time or both at the same time using a tee? The Clymers I have doesn't mention
this and it seems like they should have addressed it!

HELP. Will be back at it in the AM.

[almarconi]

Not sure what bike you are working on. When you rebuilt the rear master cylinder did you use brake fluid when you reassembled it? You need to get some fluid in there to prime it. Fill up the reservoir and loosen the banjo bolt at the master cylinder. Pump the pedal a couple times and see if you get the fluid to leak out. If you do, close the bolt and loosen the bolt at the caliper. Pump it a couple of times and see if you have fluid coming out of the brake line. Did you replace the brake hose? A 30 year old hose will be soft and it will make it difficult to get a firm pedal. If the hose is filled with rust/old fluid it will contaminate your freshly rebuilt caliper. If you have fluid at the caliper, tighten the bolt and open one of the bleed screws. Put a piece of tubing on the bleed screw and submerge the other end into a clean container with some brake fluid. Keep pumping until there is no more air coming out. Open the other bleed screw and repeat. Using the speed bleeders will make it easier to get all the air out. Sometimes it helps to gently tap the caliper with a rubber mallet to dislodge any stubborn air bubble. The pedal should be firm once all the air is out of the system. My RF has two bleed screw on the rear caliper and I usually bleed them one at a time. The caliper has two piston, one on either side of the rotor. Not sure how yours is set up.

[geol]

Just able to get back to the rear brake bleed issue. FIRST, after rebuilding the stock rear master cylinder found it NO GOOD as it wouldn't pump fluid with enough force to bleed the rear caliper. SECOND, bought two SHORT Goodridge M7 speed bleeders.... wrong choice. One worked ok (the one near the bike) and the other (one on outside) was too short and you couldn't shut it closed and stop from blowing brake fluid all over the place.

The tip to check flow by undoing the front banjo bolt to see if there was flow was critical. I bead blasted the stock bleed valves and am using those now. Brake works great. I did bleed the outside bleed valve first; got it mostly clear of air then the inside where I got all air out. Rechecked.

I bought a generic master cylinder from eBay seller kingpin90602 with a 13mm bore. Plenty of squish to work the rear brake effectively. I drilled the top mount hole (it was 6mm) out to 5/16" and bolted it to the bike in the stock location. Then I drilled a hole below it with a 1/4" drill bit and stuck a stainless M6 bolt through to secure the bottom mount position. The GS1000GL bolt hole offset is 60mm and NO ONE sells a universal master cylinder with that spacing. Then I took a piece of stainless M8 all thread and test fit it and cut it to length; probably should have measured but didn't and used the U keeper from the OEM linkage rod on the bottom. At the top, there was a slotted special purpose M8 nut that you use to retain the dust seal. It is special purpose because although it is M8, the head uses a 10mm wrench and as I said, it has the slot. I used an M8 bolt to lock the top fitting in place. System works great now... onto the next issue. Thanks! This is the m/c as I got it from eBay:

[almarconi]

Glad you got it sorted out.

[geol]

Hey! A great mechanic like me can make a one hour job into a 3 day adventure. Vintage is the Greek word for "problem" hehe