No dice on all counts. I did try adjusting the drums a little tighter and ended up with them too tight, so I backed them off a little. They're pretty much where they should be. Vacuum bleeding was no help either. I have good, firm pedal with the engine off, total mush with engine on. Crap.

I guess I'm going to go get some stock wheel cylinders and see what happens. Any last minute suggestions before I start yanking off perfectly good parts and replacing them with other perfectly good parts that may or may not fix the problem?

Thanks, guys. I know this is a PITA, but I appreciate the help.

 

OK, now I'm reallystumped and hope you guys can help me.

New stock-size master cylinderis on the truck.

The truck, however, continues to demonstrate an incredibly soft pedal. I have adjusted the rear drums so that the shoes are just slightly touching the drums. I can hear it and feel slight resistance when I turn the wheels. The parking brake is high and firm and grabs better than it ever has. Brakes are hot after a drive so I know they're working, just not as well as they should and the pedal is mush.

I have been over every inch of brake line and every union looking for a leak. You would think that under pressure, it would show fluid leaking out where the hole was, correct? No signs of leakage anywhere. Am I wrong that a leak would at least drip when pressure was on the system?

I tried wrapping the bleed screw threads with teflon tape, thinking that they were introducing air to the system when I cracked them open. No change.

I bought a new vacuum bleeder today thinking my old one was not holdingvacuum,and at 20-25 inches of vacuum, I just slightly crack the bleed screw maybe 1/16 of a turn or less--just barely. The fluid in the reservoir bottle of the vacuum bleeder percolates and bubbles, but no fluid comes out. There's clearly air in there somewhere, but with the amount of fluid I've moved through it, I can't imagine where. Opening it further, some fluid comes out, but the bubbles are bigger and more rapid.

I have now been through about 8 pints of fluid, and still have the soft pedal. Fluid is obviously being pulled through, but there is still air somewhere in the system. I tried the vacuum bleeder at all 4 corners with the same result. Air is not leaking past the vacuum hose at the fitting because it holds 20+ inches of vacuum pretty well.

The pedal is pretty solid without the engine running, but with boost it goes to the floor. I should note that before I did any work, the pedal was high and solid with no problems.

So what the heck am I doing wrong? What am I missing? This shouldn't be this hard, right? Any advice? Someone want to come over and do this for me because I'm a retard? I'm already10 days and $1000 into this project--I'll pay you just to get it done!

Jeez, I hate this $&#*ing truck. Next time I'm getting a Chevy.

 

Sorry for digging up an old post, but I am having this exact same issue and have had no luck resolving it. I have done pretty much the same things with zero improvement. I have tried to contact the OP with no luck so far.

Anyone have the magic bullet?

 

With the ABS on these trucks if you change a major component like the master cylinder and you allow large amounts of air into the ABS module then you need a way to hold the module valve in a centered position in order to bleed the brakes correctly. You could possibly try to bleed the brakes with the key in the run position and without the engine running.

 

I only have the rear wheel ABS. What tool is it?

 

It looks like a piece of steel with a notch cut down the center of it and it locks the valve from shifting back and forth allowing air pockets. its really nothing fancy and if you were in a pinch to do it I would say a good pair of small vice grips would probably grip it well enough to hold it.