Pulling my hair out...HELP...brakes

[GMC-YA68]

Here's my story

Recently acquired a 1973 GMC 3500 dually. Sat for years before I ended up with it. Passenger rear wheel would NOT roll when I got it. We had to winch on and off the trailer.

I first went straight to the fronts and put new calipers, pads, and replaced both rubber brake lines because they were rusted shut and barely had fluid passing thru them.

The truck would "drive" but brakes have always sucked. At this point I haven't done anything with the rears. (Besides hitting the locked up one with a hammer to break it loose)

I then put a new rubber line on the rear, the one that T's to each rear wheel.

Drove around the block and brakes still were very hard. The next night the one of the rear wheel cylinders let go. Ended up replacing both sides. Kept shoes and drums as they were.

Bled everything, still no change. Then the next day...brakes went to the floor, no pressure. I replaced the master cylinder (bench bled it) and installed, brake pedal turned hard as a rock again.

Put a new booster on today. No change at all. Except for a massive vacuum leak sound.(hissing) It's the check valve going into the booster. It is very noisy and causing the truck to raise it's idle 1000rpms. I can pull that and stick my finger over it and the hissing completely disappears and my idle returns to normal.

Pros; what's the fix here.????

[TrailerTrash]

sounds like the check valve or one of the hoses could be cracked. did you replace the check valve?

[GMC-YA68]

Yes, new booster came with one. Also tried the old one and no change. It has plenty of vacuum at the check valve but is the booster supposed to be air tight? It acts like it's just pulling air straight thru from somewhere.
Posted via Mobile Device

[homemade87]

You should have no volume pulling thru the booster while engine is running . It should hold a steady vacuum ( just like you put your finger on the check valve . Sound like to me you got a bad booster and is leaking . If you can here a steady vacuum pull thru the check valve you need to return it and get another .

[GMC-YA68]

Originally Posted by homemade87

You should have no volume pulling thru the booster while engine is running . It should hold a steady vacuum ( just like you put your finger on the check valve . Sound like to me you got a bad booster and is leaking . If you can here a steady vacuum pull thru the check valve you need to return it and get another .

Winner winner chicken dinner. Swapped out another booster just now. Fixed everything. Truck stops on a dime. Frustrating brand new parts like this fail out of the box but shut happens I guess. Thanks for the help.

[TKCR]

Originally Posted by GMC-YA68

Winner winner chicken dinner. Swapped out another booster just now. Fixed everything. Truck stops on a dime. Frustrating brand new parts like this fail out of the box but shut happens I guess. Thanks for the help.

Happens even in a new car manufacture plant. You'll get a bad part from time to time. I've even heard of an engine throw a rod on the first test drive around the test track.