brake problem after booster/master install

[70CHEVYBB]

I had a friend ask me to put on a power booster and master cylinder on his 48 ford. I found a 7" booster with a corvette master cylinder. I hooked up the rear brake line to the first port closest to the booster and the front brake line to the port farthest away from the booster. The master points to the rear of the truck. The problem is the front brakes lock up real easy. I am thinking I my have to reverse the brake lines. Any thoughts

[buggy5872]

it is is front disc and rear drum, I would switch the lines. Is the master for a 4 disc brake car or disc drum?

[OrrieG]

I think you are missing the proportioning valve, the lines are two different sizes (larger for front discs, smaller for rear drums) and cannot be interchanged. If you have the brake lines connected directly to the master cylinder you do not have the ability to "Proportion" the pressure front to back. you also loose the ability for the front or rear to work independently if there is a failure. Depending on how the mc is mounted you might also need check valves in the lines to maintain pressure and keep one end from doing all the work.

[mr48chev]

From looking at a Corvette brake parts supplier I am pretty sure that you have the MC connected correctly.

If it's disk/drum are the rear brakes adjusted correctly?

Or it may be that the power brake set up is working a lot better than he expected and he needs to get used to driving the car. When I had a booster on the firewall and disk/drums on the 48 the brakes would really hook up when you pressed the pedal and if someone who was used to having to really push the pedal hard to stop drove it they usually locked the brakes up.

[Chevette]

OrrieG wrote "I think you are missing the proportioning valve" and that would be my bet also.

[G&R's57GMC]

Reverse the lines, install an adjustable proportional valve in the rear line.

Does he have rear disc brakes ? If not you'll have to add a 10# residual valve in the rear line also.

[70CHEVYBB]

The truck has been driving with a manual brake setup for some time. It has a 70 camaro front sub frame and the camaro rear end. It is disc and drum. It has the camaro proportioning valve mounted on the frame beside the master (booster and master mounted to frame).

[mr48chev]

Along with having the rear brakes adjusted correctly have you got all of the air out of the rear brake lines?

One thing came to mind, does the front happen to have high performance pads on it while the rear just has standard lining on the shoes? I haven't run into problems with that but it could be that the rear shoes don't have a friction coefficient that is up to what the front brake pads have.

[70CHEVYBB]

I power bleed the system so I know there is no air. I just talked to the owner and he tells me that his brake are 8 or 9 years old. I think I will pull the rear wheel and look tonight.

[mr48chev]

Good idea. the pistons or some of the pistons may be stuck in the bores.

[70CHEVYBB]

I checked the brakes and everything is good. I did adjust them up some in the rear. I re bleed the system and fount no air. I think I was maybe jumping the gun a little as today after work I est drove it and everything seems to work well. Thanks for all the in put

[mr48chev]

Good deal on everything seeming to be working ok. And hey, you got us to work our brains a bit and that isn't a bad thing.

[Maximus]

do the brakes hold pressure / drag after being applied?? it sounds dumb, but i bought a "kit" with a MC/Booster/Bracket and my "Kit" was universal parts thrown together... the push rod was too long and held the MC piston in...... something to check if brakes are dragging..........

[70CHEVYBB]

No they release just fine. I have ran into the long booster rod that hold the brakes on.

[Maximus]

cool, glad to hear things were resolved