john, i don't think the rear brakes are the primary problem. the brakes were functioning
prior to replacing the master cylinder. i checked them and replaced the front pads and rear shoes about two months ago. i decided to replace the master cylinder and front calipers because the pedal pressue was slowly leaking down after applying pressure to the brake pedal.
I agree that plugging the port for the rear brake line at the master cylinder should eliminate the rear brakes as being part of the problem.
If I understand correctly, the brake pedal was going down gradually when the vehicle was stopped and in gear before you replaced the master cylinder and front calipers and now you have the same problem only it is worse.
Bleeding the brakes is critical and can be deceptively difficult. I've attached the proscribed procedure for your truck. It is pretty straight forward, but you must be absolutely certain there is no air left in the system. You may have to refill the master cylinder a couple of times before you get all the air out. When you stop seeing air come out of the bleeder, bleed it again through at least four pedal strokes.
I also agree that the adjustment on the rear brakes is most often a contributing factor. Plugging the line at the master cylinder prevents the rear brakes from contributing to the problem to a degree, but does not insure that they are properly adjusted nor does it guarantee that the problem is only in the front.
I hope this helps,
NOTE: Bleed primary and secondary hydraulic brake systems separately, bleeding longest line first on each system. Do not allow reservoir to run dry during bleeding operation. Never reuse fluid that has been drained from hydraulic system.
KEN, I HAVE DONE ALL THE THINGS THAT YOU SUGGESTED AND I STILL HAVE THE SAME PROBLEM (VERY LITTLE BRAKE PEDAL PRESSURE, ESPECIALLY WITH ENGINE CRANKED)? COULD THE PROBLEM BE WITH THE POWER BOOSTER? I CHECKED THE VACCUM PRESSURE AT THE BOOSTER AND IT SEEMS TO BE VERY GOOD. I HAVE NOTICED THAT WHEN DRIVING THE VEHICLE THERE SEEMS TO BE SOMEWHAT BETTER PEDAL PRESSUR WHEN THE ENGINE IS REVED UP FAIRLT HIGH.
I think I may have miss understood the problem. I'm not sure I understand what you mean by brake pedal pressure.
Do you mean that the amount of pressure you must exert on the brake pedal to make the truck stop is excessive? That would indicate a problem with the power booster, especially if it improves with higher engine RPMs.
Or by brake pedal pressure, do you mean that the pedal still gradually goes to the floor when you step on it and the brakes don't hold?