LD Hack
Member
I've been battling rear brakes on my GL1100-sidecar rig for a long time. Problem I'm having is bleeding the rear brakes. I have two brake lines coming off the master cylinder on a dual banjo bolt, one line for the rear brakes, and one line for the sidecar brakes. It's been that way for years and worked fine. Spongy brakes, I discovered a bad line on the sidecar. I now have steel braded lines throughout the machine. Brand new on the sidecar in two locations, and another braded line on the motorcycle from 2 years ago. No sign of leakage at any of the joints.
Putting things together, I also rebuilt the master cylinder. It would not hold the circlip, so I found a used master cylinder with 11,000 miles on it, very new looking. I replaced the rubber parts and used the old plunger, since it has a "screw" on the shaft of the plunger that's between the two rubber valves inside the master cylinder brake cylinder. Not able to bleed the brakes to solid, I went with the kit plunger, which has the star shaped plate covering three bleed holes. This star shaped plate pushes against the rubber valve that's on the end of the spring. The original "screw" style plunger has no holes or star shaped plate covering the holes.
I tried bleeding brakes using the brake pedal method with speed bleeder on the motorcycle and regular bleeder on the sidecar brakes. I got some pedal out of it, but not adequate.
Eventually I tried using a vacuum pump, which under higher vacuum started pulling air at the bleeder. My guess is the air is coming in through the outer rubber valve on the brake master cylinder. What I'm referring to are the two rubber valves inside the master cylinder. One is on a spring, and the other is on the plunger. I'm referring to the one on the plunger. I don't think air is coming through the banjo fittings at the master cylinder, although that's another potential source. I replaced the banjo bolt washers, although the bottom one against the master cylinder is steel, because I couldn't purchase a copper one locally. I can't see any abrasions or signs of damage to the brake lines anywhere. No sign of fluid leakage on any lines or at no joints.
My next bleed attempt is to pressurize the brake reservoir and bleed the brakes using the pedal and the pressurized reservoir. I just set that up and haven't gone though the bleeding process.
What am I missing? How come this is so difficult?
Is there a small bleed hole in the master cylinder that needs to be cleaned with a small wire? I know of this requirement for the front master cylinder. I've looked for a hole, and I can find only one. It's the one behind the reservoir hose barb, and it's pretty good sized. There are the three holes in the plunger, behind the star piece on the end of the plunger. Those are the holes, I assume, that relieve fluid pressure and prevent the brakes from locking up when the fluid gets hot. Am I right?
The summary of my problem; I believe when I'm bleeding the brakes, that on the down stroke of the brake pedal, I get fluid to move in the brake line. My guess is that on releasing the pedal, instead of the brake system filling with only fluid from the reservoir, that it is also sucking air. I'm guessing it's the rubber valve that's on the plunger of the master cylinder. How to overcome that???
If you're with me still, congratulations. This is still a tough one to figure out. I wish I had a mechanic who is good so I can hire him to fix this for me. Unfortunately, it appears I'm on my own.
Putting things together, I also rebuilt the master cylinder. It would not hold the circlip, so I found a used master cylinder with 11,000 miles on it, very new looking. I replaced the rubber parts and used the old plunger, since it has a "screw" on the shaft of the plunger that's between the two rubber valves inside the master cylinder brake cylinder. Not able to bleed the brakes to solid, I went with the kit plunger, which has the star shaped plate covering three bleed holes. This star shaped plate pushes against the rubber valve that's on the end of the spring. The original "screw" style plunger has no holes or star shaped plate covering the holes.
I tried bleeding brakes using the brake pedal method with speed bleeder on the motorcycle and regular bleeder on the sidecar brakes. I got some pedal out of it, but not adequate.
Eventually I tried using a vacuum pump, which under higher vacuum started pulling air at the bleeder. My guess is the air is coming in through the outer rubber valve on the brake master cylinder. What I'm referring to are the two rubber valves inside the master cylinder. One is on a spring, and the other is on the plunger. I'm referring to the one on the plunger. I don't think air is coming through the banjo fittings at the master cylinder, although that's another potential source. I replaced the banjo bolt washers, although the bottom one against the master cylinder is steel, because I couldn't purchase a copper one locally. I can't see any abrasions or signs of damage to the brake lines anywhere. No sign of fluid leakage on any lines or at no joints.
My next bleed attempt is to pressurize the brake reservoir and bleed the brakes using the pedal and the pressurized reservoir. I just set that up and haven't gone though the bleeding process.
What am I missing? How come this is so difficult?
Is there a small bleed hole in the master cylinder that needs to be cleaned with a small wire? I know of this requirement for the front master cylinder. I've looked for a hole, and I can find only one. It's the one behind the reservoir hose barb, and it's pretty good sized. There are the three holes in the plunger, behind the star piece on the end of the plunger. Those are the holes, I assume, that relieve fluid pressure and prevent the brakes from locking up when the fluid gets hot. Am I right?
The summary of my problem; I believe when I'm bleeding the brakes, that on the down stroke of the brake pedal, I get fluid to move in the brake line. My guess is that on releasing the pedal, instead of the brake system filling with only fluid from the reservoir, that it is also sucking air. I'm guessing it's the rubber valve that's on the plunger of the master cylinder. How to overcome that???
If you're with me still, congratulations. This is still a tough one to figure out. I wish I had a mechanic who is good so I can hire him to fix this for me. Unfortunately, it appears I'm on my own.