poor braking
 

changed from stock front drum brakes to lightweight front disc brakes and used master cylinder required 1-1/8 bore brake pedal is hard as a rock car does not slow down checked the ratio on the brake pedal measures perfect the car is a 72 dart any help is appreciated

Re: poor braking
 

Have a used once Wilwood Master cylinder for sale.

Dan

Re: poor braking
 

On our 72 charger when we changed breaks from power to manual the linkage under the dash had to be changed to a different hole to give us more of a mechanical advantage. I want to say the bore in the master cylinder was smaller making it easy to build psi.
Good luck.

Re: poor braking
 

Like Larry said, at least on Fords, the manual brake cars came with a different brake pedal, with a pivot for the master cylinder pushrod closer to the pivot for the pedal itself, for more mechanical advantage. Again, with my Fords, manual master cylinders a re usually a smaller bore, like 7/8" or 15/16" diameter, compared to over 1" for a power brake application.

Re: poor braking
 

As was mentioned pedal ratio is critical .If the car originally had power brakes the ratio was only around 4 to 1 ,a ratio of 6 to 1 is considered ideal . also ,If you are only using discs on the front and retained the drums on the rear ,a master cylinder with a smaller bore will help.
On a disc /drum car I usually use a 1 3/32 bore master cylinder which wit the 6 to 1 pedal usually will yield around 1000 psi with reasonable pedal pressure.

Re: poor braking
 

On my ‘71 Duster, I used an aluminum master cylinder that came on the Volare/Aspens. I have Strange fronts and stock 10” rear drums and factory proportioning valve also from Volare/Aspen. Never a problem stopping or holding the car. You could have a bad brake hose or a stuck caliper. Make sure too use the braided front brake hoses.

Re: poor braking
 

Any particular reason to only use braided front brake hoses?

Re: poor braking
 

All our A bodies have 7/8 or 15/16 Cylinders
The large one would not let my elder legs hold
the two step or stop quickly.
We try for 7:1 and sometimes redrill the brake petal
itself and relocate the master if need on several of our
different stockers. Particularly on the two Aspens F Body cars.

You will figure it out.
PM me if needed.

Re: poor braking
 

The rubber fatigues and expands producing
a spongy petal.

At a minimum replace the stock lines every few
years.

Re: poor braking
 

thanks for the info does anyone have the part number for the volarie style master cylinder? would i be better off going back to the stock master cylinder? also i was told to delete the proporting valve all together was that a bad idea?

Re: poor braking
 

I race the Cuda without the valve.

Re: poor braking
 

I ran stock hoses with the factory disc. I believe with the Strange brakes you have to use the braided line for the required fittings. Like John said they don’t expand giving a firm pedal.

Re: poor braking
 

You can look up the part number on Rock Auto.
This is a dumb question, but do you have the lines hooked up to the proper ports on the master cylinder? Front to the rear and rear to the front.
Did the car have a power booster in it originally? Like someone else said in an earlier reply, the pedal ratio could be the issue.

Re: poor braking
 

Don’t use the stock type rubber hose over time it will deteriorate and will cause a restriction on on the return flow back to the master cylinder.

Re: poor braking
 

Change the master cylinder bore to a smaller diameter, I usually use one inch. The smaller the bore of the master cylinder the more force at the wheels. Pascal's law is used to calculate a well balanced brake system.


14.3 Pascal’s Principle and Hydraulics | University Physics Volume 1 (lumenlearning.com)

Re: poor braking
 

Don't forget the hose between the frame and the rear axle.

Re: poor braking
 

thanks for all the info parts are ordered

Re: poor braking
 

If installing Disk Brakes in the front and keeping the stock rear brakes you should install a Residual Pressure Valve i'm not too sure about the one you should use a 2 LB or 10 LB between the Master cylinder and the rear brakes according to Strange Engineering it also says to replace the 3 rubber hoses and install 3/16 steel lines


Kenney Kelley

Re: poor braking
 

Didn't the Disc Brake master cylinders have a residual
pressure valve right before the lines factory. It looks like
it would install in any mopar cylinder. We do not use any
on all our race cars. I worry about even a small amount of drag.

Re: poor braking
 

If you really want to diagnose then you need a pressure gauge. As someone mentioned smaller bore MC means increased brake pressure but also less fluid volume per stroke. Larger bore less pressure but more volume. Rock hard pedal is good but you might have other problems. What condition are the back brakes, most assume everything is good if they aren't leaking but wheel cylinders freeze up, good pedal just no braking action.

Re: poor braking
 

Many moons ago when I worked on cars for the general public, a customer brought in an early '70's Dodge van with a leaking master cylinder. We ordered out a new master, the parts house delivered it, we bench bled it and installed it, and all was fine except that you couldn't stop it without the brakes grabbing so hard it wanted to put you through the windshield. Calling the parts store and re ordering it and returning the first one revealed that the first one was for manual brakes, not power. It had a smaller bore and that caused there to be much more line pressure than the larger bore unit intended for the power unit.It may have been packaged wrong, who knows now. There is a decided difference between manual brakes and power assisted brakes as to the bore diameter.