Answer

The booster works just like a vacuum booster. All it does is increase the pressure on the master cylinder to make the truck stop with less pedal effort. If the front brakes are locking up, you need to first determine if the rear brake are even working. If for some reason they are not, then that leaves all of the stopping effort to the fronts. If they lock up as soon as you hit the pedal, I would be more concerned about a combination valve as a possible cause as this valve is what distributes fluid to the front and back and determines how much goes to which system. But start by making sure you do not have a problem with the rears not working. This kind of failure would have the same causes, if it did not even have power brakes. Even a defective master cylinder could cause this kind of problem, look to see if fluid out put from it is working both front and rear, try backing off the lines a small amount at the master while someone applies pressure and see if you have fluid pressure at both. You want to avoid getting air in the system. Let me know what you find. Thanks

Expert:	Bob
Pos. Feedback:	99.8 %
Accepts:	2702
Answered:	5/4/2008

Auto Tech

Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)