Hard pedal (PB) Booster check good. Master shooting fliuid up ?

[rustytoolss]

My 62 Plymouth has an aftermarket Power brake system. The pedal is hard, the car is not safe to drive. I've checked the booster with the pedal drop test (it check good). I have 16-18" vac. Was working on it today. Remove MC from booster (8" daul) used screw driver to operate the MC piston. The front chamber(rear brakes) would shoot up a stream of fluid/ but did not see any movement from the rear chamber (front brakes) .
I could use some help here. The PO told me that the brakes never work right since the Power system was installed...He's right.

 

[MIKESPOLARA]

Need pic of your master. I think you have a Chevy master which the front port is for front brakes not the rear. Or just look at the size of each reservoir, the large one needs to go to front brakes. If both same size(Corvette master) then front port for front brakes

 

[rustytoolss]

Need pic of your master. I think you have a Chevy master which the front port is for front brakes not the rear. Or just look at the size of each reservoir, the large one needs to go to front brakes. If both same size(Corvette master) then front port for front brakes

I have a mopar style master cylinder 2 bolt type (cast iron with Black plastic tank and black caps). The booster is of the chevy style after market type with a bellcrank to operate the linkage.

 

[rustytoolss]

I've been trying to make this systm work for sometime now. The car was an orgnial manual drum brake car. Was converted to power disc front drum rear system by the PO. The problem is that the pedal is very hard, not safe to drive. I have 16-18" vacuum at idle. all new brake hoses, wheel cylinders, calipers. I've done the brake booseter vacuum pedal drop test/ checks good every time. The booster will hold vacuum over long periods of tme (like weeks) I have bleed the system many times (no air in system)
The car just always has a hard pedal , and feels the there is no power assist. The system has a 8" dual booster with a 1.125" mopar style master cylinder. Also there is no combo valve (1962) just a splitter block to the front brakes) and an adjustable pressure valve to the rear brakes.
I would like to keep the power brakes (if I can make the system work) . But if I can't make the power brake system work I'll convert back to manual brakes.

 

[MIKESPOLARA]

Change it to a 1" master. If your booster is good then that's about the only other thing that can make a hard pedal=too large bore master

 

[dan juhasz]

something is wrong with the booster

 

[rustytoolss]

Change it to a 1" master. If your booster is good then that's about the only other thing that can make a hard pedal=too large bore master

OK , But what about the fluid only shooting up from only one chamber to the MC ? is that normal ? Just asking

 

[rustytoolss]

something is wrong with the booster

Might be/ not sure

 

[MIKESPOLARA]

OK , But what about the fluid only shooting up from only one chamber to the MC ? is that normal ? Just asking

Yes, but it's usually the front disc port that does that, to do it with the rear you have to block off the other port

 

[MIKESPOLARA]

Hard pedal is 1. low vac 2. booster not functioning 3. Master bore too large

 

[Roger63]

I just went through the same thing, those small diameter dual chamber vacuum boosters are junk. I went through 3 of them with the same results, hard pedal and very little braking. Your gonna have to find a mopar booster that will work on your car. Or spend the big bucks and upgrade the whole system.

 

[rustytoolss]

Hard pedal is 1. low vac 2. booster not functioning 3. Master bore too large[

I just went through the same thing, those small diameter dual chamber vacuum boosters are junk. I went through 3 of them with the same results, hard pedal and very little braking. Your gonna have to find a mopar booster that will work on your car. Or spend the big bucks and upgrade the whole system.

I've been told that before. Was hoping to save the booster, guess not. I will compare cost, might go back to manual brake (DR Diff)

 

[MIKESPOLARA]

An 8" dual booster is not small, it provides a little more assist than a 11" single. 7" is small

 

[MIKESPOLARA]

I've been told that before. Was hoping to save the booster, guess not. I will compare cost, might go back to manual brake (DR Diff)

Change to a 1" bore master

 

[1STMP]

May also want to check your pedal ratio.
6:1 manual brakes
4:1 power brakes.
Agree with others that your MC bore is too large.
https://techtalk.mpbrakes.com/brake-troubleshooting/can-pedal-ratio-be-causing-my-hard-brake-pedal