proportioning valve or not?

[finz68]

My 1965 Coronet has been converted from power brakes to manual with a dual reservoir MC. The car still has drum brakes front and rear. There is no proportioning valve installed. Should I have one?

 

[gkent]

I think you have to make that decision based on how the brakes feel and the car stops. In a very good brake article it was mentioned that braking will change with circumstances such as a full tank versus an empty one! Only you can decide.

 

[Kern Dog]

No 4 wheel drum brake arrangement that I know of (Mopar) uses a proportioning valve. They did have a junction block for joining all the lines in a common area but that is called a distribution block.
The reason that actual proportioning valves were needed was because the differences in how disc brakes act in a linear manner while self-energizing drums have an exponential braking effect. For example, 50 lbs of pedal pressure may deliver 100 lbs of drum brake force, 100 lbs of pedal pressure may result in 300 lbs of brake force, 150 lbs of pedal pressure may result in 450 lbs of brake force. The two differing rates required the front and rear to have some form of steady balance.
A 4 wheel drum or 4 wheel disc system on OEM applications are designed with what is known as natural proportioning where the wheel cylinders or caliper sizes are chosen to deliver proper brake bias with no additional controls. The goal on 4 wheel discs is a 2 to 1 ratio where the front maintains twice the load of the rear. 66% versus 33% is one number that has been tossed around. Drum brakes? I'd assume about the same but I'm not certain. I am certain that the fronts do assume the greater concentration of force in a street car. Drag cars are different due to the radically different tire sizes...slicks versus pizza cutters....

 

[493 Mike]

Lots of cars have less friction material on the rear shoes to accomplish the same results.
Mike

 

[finz68]

No 4 wheel drum brake arrangement that I know of (Mopar) uses a proportioning valve. They did have a junction block for joining all the lines in a common area but that is called a distribution block.
The reason that actual proportioning valves were needed was because the differences in how disc brakes act in a linear manner while self-energizing drums have an exponential braking effect. For example, 50 lbs of pedal pressure may deliver 100 lbs of drum brake force, 100 lbs of pedal pressure may result in 300 lbs of brake force, 150 lbs of pedal pressure may result in 450 lbs of brake force. The two differing rates required the front and rear to have some form of steady balance.
A 4 wheel drum or 4 wheel disc system on OEM applications are designed with what is known as natural proportioning where the wheel cylinders or caliper sizes are chosen to deliver proper brake bias with no additional controls. The goal on 4 wheel discs is a 2 to 1 ratio where the front maintains twice the load of the rear. 66% versus 33% is one number that has been tossed around. Drum brakes? I'd assume about the same but I'm not certain. I am certain that the fronts do assume the greater concentration of force in a street car. Drag cars are different due to the radically different tire sizes...slicks versus pizza cutters....

Thank you. The reason I posted is my driver's side rear drum heats up to 170 degrees compared to 70-80 on the passenger side after a 30 minute drive. I had the wheel/braking assembly and bearing checked with 2 different mechanics and they found nothing.

 

[YY1]

I agree with KD, I've come to believe Mopar did a great percentage of "proportioning" with the bore sizes of the wheel cylinders and calipers, even on front disk cars.

That's why people installing aftermarket kits or a mix of OEM parts seem to have a lot of trouble.

If you use OEM stuff, get the same size cylinders as the car your calipers came from, and it works.