Soft Brake Help for a Newbie

[kennythewelder]

Oh you can also do a pressure bleed, google it.

 

[bivey77]

I'm at a total loss now. I have no brakes at all at the rear. Here's what I've done since I last posted.

I found that when I had removed the RWAL, I had actually cross-threaded the brake line fitting into the combination valve. So, I went to the junk yard and got a new combination valve, RWAL system, and the brakes lines between them all. I connected it all (with the RWAL back in).

I also replaced the master cylinder with another new one. This one, I bench bled with hoses until I saw no bubbles, I left it for a couple hours and did it again to make sure that there wasn't anything leaking. It looked good, no bubbles. I installed it and bled all of the brakes in the right order.

Now, I have no brakes. Before I bled the brakes, I lifted all 4 wheels and removed them. After bleeding the brakes, the pedal feels nice and firm when the truck isn't on. But as soon as I start it, the pedal goes all the way to the floor. With all 4 wheels on stands, I started the truck and put it in gear. The real wheels spin even with the pedal to the floor.

Also, the brake light stays on, if that helps diagnose.

Please help!

 

[east302]

Do you have both an ABS light and BRAKE light? I think the brake light is turned on when the pressure switch on the combination valve is tripped. That's when one circuit has much less pressure than the other--such as an open line or leak. But, that should close the valve, isolating that circuit, so if you're getting fluid at all four wheel then that probably isn't the case.

Sorry, that wasn't helpful at all, but this reminds me of a video I saw. Some guy with a Corvette could never get rid of a soft pedal, and it was air trapped in the master cylinder. The way the cylinder installs, it is sloped down toward the firewall. By jacking up the rear of the vehicle, the front of the cylinder was lower than the rear (at the booster) and he managed to get the air out by slowly pumping the brakes.

No guarantees, but it's with a shot in your case.

Edit: here it is. I don't know if it's even the same type of MC.

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There was a thread where someone bench bled by using a woodworkers clamp to keep the piston compressed. He then tilted the MC up and down to get all the bubbles out. I think this accomplishes the same thing that the Corvette guy was saying.

http://www.tahoeyukonforum.com/threads/master-cylinder-bleeding.98532/




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[bivey77]

Thanks for the suggestion. I actually started this whole process by just jacking up the rear. Just recently, I've jacked both the front and rear. There doesn't seem to be a difference, at least in my case.

And there is just one brake light, no ABS light.