Power disc brakes

[Dep]

Question, my jeep came with factory front disc/rear drum, I have a power brake set up that I want to install, its for the set up i have. I'm also looking at a rear end to swap into it, and it already has a rear disc conversion, is this going to work with the power booster?

 

[tarry99]

The booster is only one part of the equation and it should work OK as long as you have about 21 inches of vacuum at idle..........

The master cylinder bore size for the front & rear disc has to be sized correctly to the calipers bores being used at each end as disc brakes require more fluid transfer volume each time the brakes are applied. Along those lines they also require more pressure...............if your vehicle had manual (non boosted) brakes there is a chance that the ratio at the pedal may have to be changed for the boosted system...............basic brake pedal ratio for manual brakes is about 6 to:1 while a power brake pedal ratio is about 4:1.............obviously if you had a 6:1 ratio and used that with a power booster the brakes would be quite touchy........

 

[gert]

the booster should be fine its the master cylinder that will need to be changed to a Disc/Disc MC, the conversion kits usually use one from a corvette I believe late 60s application most drum master cylinders have a residual pressure valve in them that you do not want on a disc brake

 

[Knighttime85]

I did a swap to power brakes, but kept the drums in the rear it was a simple bolt in process with the parts I used. I kept the stock proportioning valve, and piping since I didn't change the rears. The place I got my kit from sales proportioning valves with the booster and MC for stock setup or disc conversion in the rear I just had to inform them of my setup. I had them send the Disc/Disc valve for when I swap in the future. Below is a link the the place I got mine.
GPS Automotive | Disc Brake Conversions | Power Brake Boosters | Master Cylinders

 

[Lumpy Grits]

With a disc/disc deal from a disc/shoe set-up. You may have to change your proportioning valve also.
Disc brakes require much higher psi to work than the shoe type brakes do.
LG

 

[Dep]

ok, so if I stay with my disc/drum set up and all I did was add a booster, should I change the proportioning valve? I can pass on the rear axle its not a must have.

 

[Lumpy Grits]

ok, so if I stay with my disc/drum set up and all I did was add a booster, should I change the proportioning valve?

No need to.
LG

 

[Dep]

well thanks everyone, I appreciate the help.

 

[Lumpy Grits]

Post up how it all goes.
LG

 

[Dep]

will do

 

[Hedgehog]

I have to say this and it's just a word of warning. I went to front disk/power brakes on my '75. After fussing and fussing with them, I still don't like the touchy SOB's and wish I had left them alone.

 

[Lumpy Grits]

Hey HH, any clue as to why they are so touchy?
Just sounds like wrong combo of components maybe.
I have the OEM, PB setup. With my 'shoe' 9" rear axle the Jeep stops great and not touchy at all.
LG

 

[Hedgehog]

They work, I just don't like the feel of them. I'm to the point of just runnin' them and getting used to the feel.

 

[mstar]

Hedge, put a BIGGER CAM in it .that will calm it down.

 

[Lumpy Grits]

Hedge, put a BIGGER CAM in it .that will calm it down.

LG

 

[mstar]

LG

Not enough vacuum to operate booster properly.
I have a hot rod motor in a pickup with power brakes that work so so because of low manifold vacuum. it needs a electric vacuum pump but I haven't done it yet.

 

[Lumpy Grits]

How much Hg is needed for the booster to function?
How does lack of Hg make the brakes 'touchy' like HH is having? I should make'em far less so.
LG

 

[Hedgehog]

I've got plenty of vacuum. Thank you guys for the help, but we are getting off topic here. This isn't about my brakes. I though I'd just mention that it can be tricky messing with stock brakes.