Rear brakes not working

[bill_face]

Hello all,

Just got my '79 GS550 out of hibernation, and the back brake is decidedly iffy. Initially it worked, and then it stopped working, i could press it all the way down with no / extremely limited braking.

So i decided to have a little fiddle. if i pump the brake i get a bit of resistance (not sure if it brakes as I was back home by then). I decided to take the pads out and have a look at them. They have about as much left on them as the thickness of the pad back plate (~3mm).

Problem 1) When i had the pads out i pushed the brake pedal to see if anything moved. It went in on one side, but not the other (that i could see) The side that went in, didn't retract, and i pressed it again to see what happened, and it went in a bit further and didn't retract. So now the brake pad doesn't fit back in on that side.
Question: If i release the brake fluid valve and push it back in will that help my cause?

Problem 2) there are two fluid release valves.
Question: When bleeding the brakes do you do one at a time, or both simultaneously (with two spanners and bits of tube?)

Problem 3) the one valve is missing its dust cap.
Question: When bleeding are there any further precautions to take in light of this?

[Grimly]

The rear caliper is a total sod for seizing up and/or unequal application of pistons to the pads.
Only proper solution is a strip and rebuild, but if you can work the pistons in and out a few times in-situ, it will buy you some time until you need to do that.
Regarding the bleed valves, furthest away one first, then the nearest. Or vice-versa, it really doesn't matter.

[Nessism]

Bad brakes can get you killed. Do a full teardown, including the master cylinder, and clean out the grunge. Replacing the line, seals, and any corroded pistons is also highly recommended. Also, grease the lever pivot.

[rphillips]

Yep, what he said ^^^^^. Not a question, they should be like new as long as everything goes right. Be sure of getting "all" the goop and corrosion out, no pits nor grooves in master cyl. or calipers, and be careful installing seals and cups, don't pinch, tear, nor get them rolled in their groove while installing.

[zuluwiz]

And while you're in there, replace the pads. They're not expensive, but putting new, modern pads in can make a major difference. Some older bikes (like mine) still had the original pads in. They were metallic and didn.t even sweep the whole rotor. Needless to say, brake performance was sub-optimal. Your life depends on your brakes. it's not something to try to save money on.

[Finn]

I would rebuild the brake caliper and the master cylinder both and get the system sorted at once - that's what I had to do with my GS.

[bitzz]

My personal rule when dealing with almost 50 year old vehicles that I want to drive: When there's a brake issue, and I don't know the last time someone (me) has gone through the brakes thoroughly, I go through the brakes thoroughly.
The service manual will call for service and/or replacement of the master, caliper, hoses and fluid every 4 or 5 years, regardless of use.

[rphillips]

I'd never thought that. I thought only wear items in master or caliper are replaceable rubber, I wouldn't think any of the metal would wear at all.

[Grimly]

I'd never thought that. I thought only wear items in master or caliper are replaceable rubber, I wouldn't think any of the metal would wear at all.

It's corrosion that's the killer, especially on chromed steel pistons.

[rphillips]

Well yea, any damaged parts got to be repaired or replaced, but I'd think age would have nothing to do with it. I's talking about the replace every 4 or 5 yrs. If there's nothing wrong, don't waste your money just cause of the age of the parts.

[Who Dat?]

Even when everything is working PERFECTLY, if you remove the caliper from the rotor and push the pedal, only one piston is likely to move. It will always be the one with less friction at the seal. Might not be much less, but they are seldom exactly equal.

And, when you release the lever, the amount that they go back in is basically not visible. They will only go back by the amount of distortion in the profile of the seals. You will need to push them back manually. No need to open the bleeders to do that, just make sure there is some room available in the reservoir and push slowly.

Regarding the two bleeders, when you are bleeding air from the system, they both need to be done, but only one at a time. Common practice when bleeding brakes is to do the farthest bleeder first, then work toward the master cylinder.

The missing dust cap should be replaced, but it's not going to affect anything in the meantime.