Rear brake not working

[m2pete]

​

Thanks again Pieters86. My 3/8 was six-point. I bought a 12-point, and it works.

When I remove the brake line from the master cylinder and press the brake pedal, fluid comes out of the top, so I am thinking the master is ok. The fluid is clear. The only possible restriction seems to be the connection for the brake light switch (see attached). Anybody heard of fluid being stopped by this switch?

 

[Cooter]

Yes.

clear the line and banjo switch,

 

[m2pete]

Well, good news: I rebuilt the master cylinder with new parts, put everything back together, and filled the reservoir. Tried the old school method of bleeding the brake line by pumping the pedal and holding it down, opening the bleeder, closing the bleeder, then repeat. No fluid ever comes out of the bleeder and the pedal never gets hard, I think because the size of the master cylinder is very small compared to quantity of air that could be in the line? Is there a better technique, or do I need to purchase a pressure bleeder?

 

[Cooter]

the parts are still full of corrosion.

clear the line and banjo switch,

.

 

[Bueller-Bueller?]

I think your line is clogged. I would just replace it (amazon has lots of brake lines very reasonable) very least take it off and blow air it it. If the line is clear make sure the caliper moves.

 

[34nineteen]

Is fluid being pumped out of the master? Don’t worry about the bleed nipple at this point. You may need to “bench bleed” or “prime” the master first.

If a line was clogged, he would have a firm pedal.

If the master is not moving fluid, it doesnt matter what the rest of the system is doing.

The master is small enough where it’s not going to take a big air bubble to have the master (Baretts college nickname) “dry pump” (Cooters college nickname).

Start there.

Let me say it again.

Start there.

 

[Cooter]

Question for the OP.

When you "re-built the master", that included taking off the 90* plastic fitting that connects to the reservoir, Clearing that line, including the very tiny hole that feeds the master with fluid from the reservoir that is clogged with corrosion, and replacing that o-ring?

Your "rebuild" also included cleaning the fitting of the brake light pressure switch?

Disconnecting the brake line from the caliper and blowing compressed air through it?

We're trying to help you and now just guessing here, you're not doing such a great job of explaining what's happening.

 

[m2pete]

Yes, new 90 degree plastic elbow and o-ring, cleared the small hole, new piston and seals and spring. I think next step is try to force new fluid through the bleeder, after removing the line from top of master cylinder. If no flow, will remove brake light switch and one or more sections of line.

 

[Cooter]

 

[ajax5777]

I have rebuilt many a master cylinder but not one on my Buell, so I just want to through this out there cause its happened to me. And again, I have not rebuilt a Buell cylinder, but are you (OP) sure you put the part with the new cups in correctly? It will only work if the cupped rubber faces the correct direction. On some cylinders it is amazingly easy to put it in backwards, which would be much easier. Being from the school of hard knocks I've adopted a saying "if something goes together smooth and easy, you probably did it wrong". Just trying to cover everything. Good luck.

 

[m2pete]

Hello Ajax, thank you for your suggestion. I am sure the rubber cups were installed correctly, as it was clear how they went on originally, and clear how they are designed to scrape the cylinder walls. It is interesting to me that by pumping the pedal, I cannot build up any pressure, no matter how much air might be in the line. The master cylinder should be working like a one-way valve.

I am currently trying to remove the copper brake line between the reservoir and the brake light switch. Does anyone know what size socket is needed to remove the brake light switch? I tried an open-end wrench, but it is just too tight for that. The size is larger than 22mm, and less than one-inch, so that makes it 23, 24 or 25mm.

 

[Cooter]

No need for specialty tools, a decent sized syringe can be used to push fluid into the bleeder for 'reverse bleeding'.

Or something else to watch out for, if your still-filthy-not-cleaned rear brake caliper piston is sticky, it will retract back into its bore when you release the pedal, instead of staying out and causing the vacuum that's needed to draw fluid into the master cylinder bore. If that indeed is the case, you can see it happening.