Brakes anyone?

[bigred cummins]

Ok, my brother's truck (92 W250 Single Cab LE) has absolutely no brake pedal. When you push on it it goes straight to the floor. I've replaced the booster/master cylinder, rear shoes recently, and bled 3 pints of brake fluid through it to no avail. Any Ideas? (And yes, I bled the ABS thingy near the rear.)

[cougar]

I just went through this.
Adjust the rear brakes until it gets hard to turn each tire. Turn the tire in both directions to center the shoes. See if that changes the peddle.
The ABS thingy will make the brakes feel mushy, but if the rear brakes are properly adjusted, they will work just fine.
Can you pump the brakes up? If you can, do they hold pressure of slowly bleed down. If they bleed down, you have a bad master cylinder. I just had a brand new one from Napa do that.

[PToombs]

Did you replace it with a rebuilt or a new MC? Lots of stories on here about how a newly rebuilt MC was bad and didn't work.

[chrislib]

Are the caliper slides clean and lubed? If the slides stick the binding can cause the caliper piston to be pushed back in when the pedal is released.

[cougar]

I just went through 2 new NAPA master cylinders and both were bad. The Car Quest replacement is so far so good.

[Mark Nixon]

ALWAYS "bench bleed" a new, rebuilt or run dry master cylinder.
As a kid of 17 I went through 3 on a '72 Duster before the counterman asked me if I had done that.
When I looked at him blankly, he explained it.

Also have had them bleed out fine, no leaks, but have "sinking pedal" or "comes and goes hard pedal", which is an internal leak between the piston cups.

A very simple test,which is reliable enough that the DOT uses it in safety checks on hydraulic braked vehicles, is the one where you pump the pedal 3 to 5 times and hold it for a length of time, any sinking beyond, I think, 1/2 inch indicates a pressure problem and is an automatic OOSO.

Mark.