Rear Brake's Sticking

[Guest]

I haven't seen this posted yet but if it has please point me in the right direction. My 1979 GS750 has a rear brake that only sticks when either the bike gets warm or the bike is sitting outside in the Arizona heat. When the brake sticks, the bike is hard to move around but I can muscle it. It never happens when its cool in the garage and I move it around. So what I did is I removed the rear caliper and bought a rebuild kit for the caliper and the rear master cylinder. I cleaned out all the gunk in the rear master cyl but the caliper wasn't bad. I didn't replace the pads. I greased everything back up, used my mighty vac to bleed the system again with Dot 3 fluid ( I tried with Dot 4 after it), then go for a test ride. It takes a lil longer for it to happen but the issue is still there. For now I just drained the brake fluid out and ride with the front brake only. Has anyone seen this before?

[cowboyup3371]

When you cleaned the rear master cylinder, did you poke a single strand of 18 gauge wire through the extremely small return port to clear out all of the junk in it?

[602busa]

I was reading other forums about that. Anyone have a picture of the hole?

[Steve]

There have been many, MANY posts on this topic, but I'm not sure that anyone has actually posted any pictures.

I'll take a look in my parts inventory to see if I have a spare master cylinder so I can get some pics for you.

BUT, ... without resorting to pictures, here is a description:
It might be easier if you remove the m/c from the bike, but might be possible with it in place. You will need to remove the large fitting on the side of the m/c that leads to the fluid reservoir. Inside there, you will find two holes. One, near the bottom, will be one or two millimeters in diameter. The one you are looking for will be just above that, and will likely be about 0.5mm in diameter. The best way to clear that will be to take a single strand of copper from a wire, then poke it into the hole. Note that wire comes in different forms. Some 18ga wires might have 7 or 8 28ga strands, while other 18ga wires will have about 20 40ga strands. These numbers are NOT accurate, merely for vizulization purposes. This is to say that cowboyup's "single strand of 18 gauge wire" might have been one of the finer ones not the larger ones, so your experience might be different. The bottom line is to find a wire from which you can extract a single strand to poke through the hole.

.

[602busa]

You will need to remove the large fitting on the side of the m/c that leads to the fluid reservoir. Inside there, you will find two holes. One, near the bottom, will be one or two millimeters in diameter. The one you are looking for will be just above that, and will likely be about 0.5mm in diameter.

.

So this is on the actual fitting I'm removing or on the m/c after I remove the fitting?

[cowboyup3371]

On the master cylinder after you remove the fitting

[602busa]

I just took it apart. I see the holes clearly now

[Steve]

Make sure the TOP one is clean.

.

[602busa]

Funny thing is that the top one seems like its solid. Like there isn't a clog of debris, but like a solid piece. I'm using a few strands of RJ45 copper wire and nothing goes in. I tried putting an air hose to it and a lil more gunk came out. But still can't stick a piece of copper thru. I tried poking it at it lightly with a pick and I'm feeling metal. am i nuts?

[cowboyup3371]

RJ45 strands will be too thick; use a single strand of 18 or 20-gauge 12v wire for your bike

[Big T]

You greased everything?
Grease and brakes don't mix

[602busa]

You greased everything?
Grease and brakes don't mix

I greased the back of the brake pads. But I did find a strand of wire to clean out the holes. I also took my air gun to it for good measure. Went for a test ride and have no more issues. Thank you.

[Steve]

I greased the back of the brake pads.

What kind of grease did you use?

If it wasn't special grease that is meant to be used in brake systems, please do yourself a favor and degrease your pads.

I did find a strand of wire to clean out the holes. I also took my air gun to it for good measure. Went for a test ride and have no more issues. Thank you.

You are quite welcome. Thanks for the report.

.

[abaton6]

I just checked this out, as l am rebuilding the rear brake system on my GS 650. I used a wire from a wooden handle wire brush. Thanks for the tip.

There have been many, MANY posts on this topic, but I'm not sure that anyone has actually posted any pictures.

I'll take a look in my parts inventory to see if I have a spare master cylinder so I can get some pics for you.

BUT, ... without resorting to pictures, here is a description:
It might be easier if you remove the m/c from the bike, but might be possible with it in place. You will need to remove the large fitting on the side of the m/c that leads to the fluid reservoir. Inside there, you will find two holes. One, near the bottom, will be one or two millimeters in diameter. The one you are looking for will be just above that, and will likely be about 0.5mm in diameter. The best way to clear that will be to take a single strand of copper from a wire, then poke it into the hole. Note that wire comes in different forms. Some 18ga wires might have 7 or 8 28ga strands, while other 18ga wires will have about 20 40ga strands. These numbers are NOT accurate, merely for vizulization purposes. This is to say that cowboyup's "single strand of 18 gauge wire" might have been one of the finer ones not the larger ones, so your experience might be different. The bottom line is to find a wire from which you can extract a single strand to poke through the hole.

.

[canuckxxx]

I have the same problem with dragging rear brake on my '79 GS850. Maybe the master cylinder is different for the 850 because this is what I see when I look into where the reservoir connects. Those 2 holes are clear and I don't see any tiny hole that could he plugged.

Thoughts, suggestions?
Brian
rear master cyclinder where reservoir connects.jpg