Brake Help. What does this sound like??

[krause95]

So this is whats going on with my brakes. When I pump my rear brake it takes 3-4 pumps before the rear brake fully engages and then when I let off on the brake and let it sit for a few seconds I have to re-sart the pumping process to get any brakes. I thought it was the master cylinder so I rebuilt it and I just put it back on and its doing the same thing. I can't find any leaks in the brake line and they are bled. To put another twist on this, I tried using the old master cylinder that I use to have on the bike and it worked fine. That is the old style master cylinder and the one I have is newer (2001+). I would just use my old master but I already build my mid controls and every thing to work with this new style.

Any Ideas what this sounds like? Maybe the brake cylinder in the drum?

[nuklhd]

don't those new fangled disc things have something in the master cylinder,a check valve kinda thing that wont work with a drum unless you leave it out.? maybe thats it.

[andri]

The drum brake pads have these strong ass springs pulling them back away from the drums. This would press the brake fluid back into the master
cylinder.
That is why on the older master cylinders ,intended for a drum brake, like the Wagner, there is a valve that restricts the fluid from returning easily back
into the mc.
That valve is removed from the mc when used with disc brakes to allow the brake fluid to flow easier back into the mc as the fluid in the caliper warms up.

So since you fitted a newer style master cylinder, intended for disc brakes, it does allow the brake fluid to flow unrestrictedly back into your mc, due to the
high force applied by the brake pad springs, forcing you to pump your brakes every time you need them.

I am not aware of a solution, other than getting a master cylinder intended for a drum brake. But maybe someone on here can help you with that.

Sucks though, since you already put alot of work into fitting the new one.

[spidr]

On vehicles, we use a residual valve. It just threads inline, they make a 2lb for discs, and a 10psi for drums. THey're cheap and easy to fit, I'd try there.

http://www.summitracing.com/int/part...3279/overview/

[krause95]

Great, thanks guys this is super helpful I was clueless as to what was going on.... So if I buy that residual valve that should help/fix the problem? Should I get the 10psi one for my drum brake or what do you recommend?

[spidr]

I cant personally attest to wether or not the old master would have the residual valve built in, but that is what it sounds like. We use them all the time with trucks we build, and yes you want to 10psi, the 2 psi just wont cut it.

Again since I dont know harley drums though, is there an adjuster like a car? You'll get a similar effect if its not adjusted properly, becuase the wheel cylinder needs to take up the gap before it applies the brakes.

[krause95]

Yeah I guess I'm not entirely sure what you mean by the adjuster? Would it be on the drum or the mc or both?

[spidr]

On hydraulic car brakes, there is a star wheel adjuster at the bottom of the drum, opposite the wheel cylinder. They're normally self adjusting, but need to be initially adjusted to work.

Actually, just realized that you said it works fine with the old master........Disregard. Put the residual valve in.

[krause95]

Ordered the valve last night, I'll post if it helps or not