Issues Adding Power Brakes 54 Chevy

[Nick Z]

I am adding and under the floor 47-59 Chevy/GMC Truck, Power Booster Kit (Part# BB-T4755) to my 3600 series 54 Chevy pick-up.

Kit instructions that I followed: https://www.performanceonline.com/bl...r-booster-kit/

I have run into a few small issues in the process. The initial kit purchased from Tuckers appeared to be missing a few pieces to connect the pedal to the booster, I ended up using a Heim bolt and thread all to connect the booster to the pedal. It feels like I have the correct rig so the it does not press up on the pedal and it does not press into the booster when at rest. I was having trouble getting the pressure to build up on the bleed(s). I discovered every since wheel cylinder was corroded to hell, so I replaced all of them. I also replace most of the brake lines so that they could connect to the correct ports on the master cylinder (front lines to the aft port of master and rear to the front port of the cylinder.) I am still having issues getting the bleed to build up enough pressure to stand on the brake pedal with the engine off. I am able to build a little pressure, but as soon as I turn the engine on the pedal goes to the floor when pressed. I tried to reverse bleed without positive results. I also tried to use the bleeding hand tool without positive results. I then tightened all of the brake pads so that they scrape a little when I spin the tires while on jacks. I then did a test with the truck on jacks by spinning the tires and having someone press the brakes. The tires do stop, but I am still not getting the amount of pressure I want on the pedal, as I did with the old master installed. I called Performance Online Tech support and Tuckers, but have not been able to figure out the issue. They told me I MIGHT have a bad part, either cylinder or booster. Please let me know what I can try to fix the pressure issue. Thanks.

[dwcsr]

You have several issues that I can see. First being that the master cylinder bore may be to small and that's why your not getting a pedal. It needs to be 1.25" minimum for 3600 and 3800 trucks

You need a 1/2" spacer between the hiem and the pedal tab so it lines up better.

The linkage your using has to have at least 1/2" thread engagement in each side of the connector and into each end. Don't' use the clevis on the pedal use the heim joint

I'm not sure why they sell this for 3600 and 3800 they must know by now it doesn't work. Your not the first with this issue and a POL booster kit

[Nick Z]

Originally Posted by dwcsr

You have several issues that I can see. First being that the master cylinder bore may be to small and that's why your not getting a pedal. It needs to be 1.25" minimum for 3600 and 3800 trucks

You need a 1/2" spacer between the hiem and the pedal tab so it lines up better.

The linkage your using has to have at least 1/2" thread engagement in each side of the connector and into each end. Don't' use the clevis on the pedal use the heim joint

I'm not sure why they sell this for 3600 and 3800 they must know by now it doesn't work. Your not the first with this issue and a POL booster kit

I really appreciate the reply. The kit did not have the spacer with it, I will see if I can find one at a hardware store or make one so it lines up a little better. About the 1/2" thread engagement in each side of the connector and into each end, do you think that could be effecting my pressure? Do you think I should install a thread all that is pushing on the pedal and on the booster a little more than rest in-between both? I will look at the bore issue after I can get easier items fixed. Thanks.

[dwcsr]

The tread engagement is for safety, the threaded rod needs to be into the connector and rod end at minimum of 1.5 times the diameter of the rod so it does not pull out or snap off under a hard stop. It has no effect on pressure

The spacer is 1/2" wide with a 3/8" hole , you will need a longer bolt,

I've done many 3600 and 3800 trucks and its the reason we make our own master/booster kit that's the correct size.

[Nick Z]

Originally Posted by dwcsr

The tread engagement is for safety, the threaded rod needs to be into the connector and rod end at minimum of 1.5 times the diameter of the rod so it does not pull out or snap off under a hard stop. It has no effect on pressure

The spacer is 1/2" wide with a 3/8" hole , you will need a longer bolt,

I've done many 3600 and 3800 trucks and its the reason we make our own master/booster kit that's the correct size.

Ok, the treads are engaged fully into the rod ends. I will get that spacer, thanks for providing the hole opening dimension. I was reading about MC bore sizes and I read that a smaller bore means more pressure, or excessive pressure. http://www.markwilliams.com/braketech.aspx

If at all possible I would like to see if I can get this kit to work for me. How much do you charge for your kits, or what MC do you think I could use that would work with this kit if I can't get this MC to work.

[dwcsr]

Originally Posted by Nick Z

Ok, the treads are engaged fully into the rod ends. I will get that spacer, thanks for providing the hole opening dimension. I was reading about MC bore sizes and I read that a smaller bore means more pressure, or excessive pressure. http://www.markwilliams.com/braketech.aspx

If at all possible I would like to see if I can get this kit to work for me. How much do you charge for your kits, or what MC do you think I could use that would work with this kit if I can't get this MC to work.

Required line pressure is more than just bore size, its a combination or pedal leverage, bore size in the master and the wheel cylinders or Disc caliper bore size, and fluid volume moved and weight of vehicle and what it takes to stop it

All things being equal, pedal leverage, wheel cylinders, the smaller the bore the higher the pressure but the lower the volume. larger bore lower pressure but more volume. You figure out how much volume you need and then go with the appropriate master. So if you have drums all the way round they need less volume. The master stock should be 1.125 diameter. Disc front need more volume so you may go with 1.25" master. Drums need less PSI to operate. Adding a booster crates more line pressure when going up in master size. So you could have 800PSI on a stock system but get 1000 psi with a single diaphragm booster

How do you know what PSI you have, You need a pressure gauge setup for the calipers and have someone press the brake pedal at a normal foot pressure and again at a hard stop foot pressure.

From experience I know I can get 1200 to 1400 PSI from a stock pedal ratio with a 7" dual diaphragm booster and a 1.25" master that will operate 4 wheel disc brakes with dual pistons and 13" rotors. I also know that moving to a 1.3 or 1.5" is to much brake for these trucks, the 1.25 engages the brake at about 3/4 pedal and stops it without skidding. It stops an 8600 lbs truck nicely.

But remember this is for 3600 and 3800 trucks not 3100 trucks