Pick your brain about brakes

[Varnae]

Ok, so as many of you know, my bike is at my mechanic right now. He's got it running and from what he says it sounds great. The only problem now is that it won't stop. He's having issues with the brakes and I just wanted to pick your collective brains to see what you thought about the situation. On both the front and rear brakes, when you depress/squeeze the brake lever nothing happens. He has already made sure that there there is no air in the lines and it has brand new brake fluid in it. To show me, he took the top off the rear master cylinder and pushed down on the brake pedal, now when he does that (in theory) brake fluid should flow into the reservoir. The problem is that it doesn't seem to do anything. He says he's going to have to do a master cylinder rebuild on both the front and the back. But I can't help but wonder if the wheel cylinders are frozen. If that were the case though, wouldn't the fluid still fill into the reservoir? What do you all think?

[CatatonicBug]

When you press the brakes, fluid should NOT flow into the reservior. It should flow to the caliper. When you let OFF the brake, it flows back into the reservior though. One quick way to tell is to remove the line from the MC and hold your finger over the hole while pressing the piston in. If fluid shoots out past your finger, then the MC is still good (though there is still a chance that there is a small amount of leakage past the seals). I would suggest plugging the port where the line connects and squeeze/press the brake, and see if that stops the movement of the piston. The filler cap on the rear MC is the same thread as the banjo bolt and works great as a plug. If you can squeeze like crazy, and the piston won't go in, then the problem is further down the line - either air in the line or a leaky caliper. If you can afford it, and you don't know how long it's been since your MCs were rebuilt, it wouldn't hurt to replace the rubber in them though. They can get a little pricey though ($75 each, depending on the model). Has your mechanic taken the calipers apart yet? In this process, I would suggest using either the MC or compressed air to push the piston out of the caliper and clean/check the seals in there too. Be sure to have him clean UNDER the seal on the piston, in the little groove. Lots of gunk builds up there. HTH

[andysutt]

I just got done redoing my rear brakes.

My bike had no rear caliper on it when I bought it. Just the mastercylinder and the hose.

I don't know what was messed up, but when I added the caliper, took the top off the master cylinder to top it off and bleed the brakes... There was already fluid in there. It should have leaked out.

I pressed the brake peddle and nothing... caliper wouldnt move or anything.

I do know the mastercylinder/hose that came with my caliper was good, so I went ahead and swapped all of that.

Anyways, my point is, if your pedal moves but nothing happens, I would say its the mastercylinder not the caliper because my caliper would move while pressing the plunger on the new mastercylinder even w/o much brake fluid in it due to air pressure. I'd start with the master cylinders for sure.

[CatatonicBug]

There was already fluid in there. It should have leaked out.

Not really. If the MC is still mounted on the bike, and has a piston in it, the path between the reservoir and the outside world is blocked by the piston. That's why there are 2 seals on the piston. You can even ship these things around and the fluid will stay in them, unless you remove the piston.

I would definitely start with the MC as a culprit though. Try to get a pressure build-up wth your fingers, then with a mechanical block (like the filler screw) to determine the seal quility of the piston.

[andysutt]

Not really. If the MC is still mounted on the bike, and has a piston in it, the path between the reservoir and the outside world is blocked by the piston. That's why there are 2 seals on the piston. You can even ship these things around and the fluid will stay in them, unless you remove the piston.

I would definitely start with the MC as a culprit though. Try to get a pressure build-up wth your fingers, then with a mechanical block (like the filler screw) to determine the seal quility of the piston.

The reason I said it should have leaked out is due to the fact that the brake lever has been moved a ton of times, and should have pumped out the fluid.

What was on my bike when I got it was the master cylinder and hose.. no caliper. The hose was just zipped tied up out of the way. By pumping the brake lever, it should have came out

[fredintoon]

- - The only problem now is that it won't stop. He's having issues with the brakes and I just wanted to pick your collective brains to see what you thought about the situation. On both the front and rear brakes, when you depress/squeeze the brake lever nothing happens. - - - He says he's going to have to do a master cylinder rebuild on both the front and the back. But I can't help but wonder if the wheel cylinders are frozen. If that were the case though, wouldn't the fluid still fill into the reservoir? What do you all think?

Hi Varnae,
did the brakes ever work or what? When you say "nothing happens" do you mean the pedal and lever sink down but the brakes don't work or do you mean the beggars are solid and don't move?
If it's soft lever/pedal could be air in the system &/or bad master cylinder.
If it's solid pedal/lever, yes, the caliper pistons could be frozen.

[dbeardslee]

There's a seal thing on the plunger in the front master cylinder. If you squeeze the brake handle too far when you're trying to bleed that little sucker will pop right off its mount. Supposed to put a piece of 2X4 between the break lever and the handlebar to keep it from happening. That's where I would look first on the fronts. Not so much of a problem on the rear as it has a different plunger arrangement. I don't know if the 81 specials have the setup where the front and rear brakes are connected, or if so if the fronts can affect the rears. My $.02.

[DiverRay]

The mechanic NEEDS TO BENCH BLEED THE MASTER CYLS!!! The brakes WILL NOT WORK if you do NOT "bench bleed". I've done a few brakes, including a complete system rebuild, and without a bench bleed, the brakes WILL NOT WORK!

[DGXSER]

FYI Doug, 81 Specials do NOT have linked brakes. Apparently the 81 MNS does.

[renegade_xs11g]

The thing with brakes is....alot of people, yeah even 'mechanics' don't know about them

Like DiverRay said, you need to have your mechanic bench bleed the M/C
even a little air inside the master, will cause them to feel spongy, or like your's, NOT work at all.....

Varnae: in your situation, the 'mechanic' has pulled the cover off, and pushed on the lever, this will push fluid out of the chamber, and then when he released lever, sucked in air! you'll never get 'em working without bench bleeding,

Andy: in your case, you got the bike without a caliper on the rear....chances are the lever was pushed a few times without the caliper on,
that would fill the M/C with air, and not push fluid out, even with an open line


if it were my bike, car, truck whatever, I'd have it somewhere else,
all, and I do mean all 'mechanics' should know,
NEVER PUSH ON THE BRAKE WITH THE COVER OFF
at least unless your are doing a bench bleed



Sorry, I just get irratated when I hear about licensed mechanics not knowing what they should
but then again, I have been around the garage for over 30 years,
I did my first brake job when I was 7

[CatatonicBug]

FYI Doug, 81 Specials do NOT have linked brakes. Apparently the 81 MNS does.

Yes, that is true. The '81 MNS is the only XS with the linked brakes. The next year's XJ had them as well.

[TopCatGr58]

Hey Varnae,

Depending on the condition of the front MC, if the reservior is all dried up, cracking, faded, etc., and IF the mechanic quotes you a price close to $80.00 including the rebuild kit for the front, UNLESS you are trying to maintain perfect stock look, it would be cheaper, easier, better to get a NEW front MC from several sources, MikesXS, Partsnmore, etc., get the one for dual caliper systems, 16mm, and then Spring for Stainless Steel braided brake lines!!!

The rear, you'll have to have it rebuilt, not as easy/cheap a replacement available for it!
T.C.

[andysutt]

Maybe someone should post a tech article on how to bench bleed for those of us that don't know how

[79XS11F]

Is bench bleeding required when you use a brake bleeding vac pump to do them?
Rob

[DGXSER]

Rob,

I know I have used a vacuum pump to bleed out a completely dry system a couple times this year, the rear system on two separate bikes. Never bled anything prior to filling the reservour and pulling the vacuum.