rear master cylinder

[audijunky]

It is mind boggling, I bought a rebuild kit from PnM. Cleaned out the old housing, brake cleaner, blew it out w/aircompressor. Installed rebuild kit for caliper. Cleaned out the brake lines, blew them out w/air compressor. Installed new parts for master cylinder. And It will not work. Clymers shows diagram that does not match the parts for mine so I am unsure of the install process. Pleas tell me if this is correct first in is the spring fat end first, then goes the little metal cap/seat for the spring(dont know which end first, I tried it both ways with no sucess) then the rubber donut piece that fits on the end of the piston(with the wide end facing inward) then the piston with the seal installed(in the middle) also wide end facing inward, then the cut washer, and finally the circlip. When installed I get no fluid pumped into the lines. when not installed I get pressure where the line connects but when I release the plunger I get suction. Seems like the punger is pushing and pulling the fluid. Hense nothing getting into the line. Please Help

[mro]

Rear brake/MC, 79F



Have not had one apart myself, but have cleaned and bled a few. Bike on center stand, remove hose to caliper, hold banjo bolt between fingers, pump pedal. Let fluid out between fingers but hold it tight enough not to let air back in. Once MC/hose bled then hook up hose to caliper and bleed that.

Keep MC full, or you will have to do it all over.


mro

[DiverRay]

You probably DID NOT do a "bench bleed". This is the proccess you need to do to get the brake fluid through the MC BEFORE you install it on the bike.
1. once the MC is rebuilt, place in a vise so you can add fluid and pump the MC piston.
2. push the piston in, cover the fitting going to the caliper, and then release the piston. I use a finger to cover the hole, so I can feel the vacum as the piston retracts.
3. After about 5 to 10 times, you should have brake fluid trying to squirt out when you push the piston. The MC has now been bench bled.
4. Install the master Cyl, and start to bleed the brakes. If yuo have a vacume bleeder, it helps a LOT. If you don't have a vacum bleeder, and are still having a problem, you can buy an oil can, the type with the punp, and put brake fluid in it. connect it too the rear caliper, open the bleeder just a little, and use the can to pump fluid into the system BACKWARDS. You will have to watch the MC resivor, as it will try to overfill before all the air is out.
Ray

[audijunky]

Ill try it as soon as I get home(bench bleed)
Gracias Fellas

[Jeff]

Experienced the exact same thing on my '78. The simplest thing to do is put a vac pump on the rear bleeder and draw the fluid thru. Either a mechanical or "redneck" (suck on a hose attached to the bleeder) vac pump work well. You can also let your finger act like a check valve on the end of the bleeder screw.... letting air out but not back in as you pump the mc. With as short as the stroke on the rear mc is, it takes a while and you might actually be moving the fluid forward but its easy to assume that its not doing anything.

[Erik the Red]

When I did my brakes, I swapped out my bleeder valves for these: Speed Bleeders (got the company from someone else on here) I think it cost me 25-30 bucks, but these things are simple to use and make bleeding brakes a snap.

I thought I got the wrong size, so the people sent me the ones I thought I needed, and said just send us whichever set you don't want. I recommend them to anyone. For my bike it was #SB 8125L all around (98% sure).