Proportioning valve after conversion

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mechanic190

mechanic190

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So I did a 73^ disc brake conversion from 72 Kelsey Haines disc brakes. For some reason a lot of Proportioning valves have popped up on here. Just got me thinking do I need to swap valves? I have new calipers rotors and manual mater all from napa. Just never even thought about the p valve
 
P valves for 73+ and Kelsey Haines close enough to run or do I absolutely need to run a 73+ one?
 
funwithfuel said:
If you swapped disc/drum for disc/drum, you're good to go.
Click to expand...

Mebbee, mebbee not

You have to understand that a proportioning valve is exactly what it says

When you start "re" engineering something, it no longer "is."

It's going to depend on the tires, the front brakes, and the rear brakes. All that can change
 
Havae you done a series of stops, increasing in hardness to see if the rornt or rear locks up? Try that and see. And if you can, try a panic stop from low speed on a wet surface too. If any lock-up front or rear is minimal and controllable, especially under hardest (panic level) braking, then you are good. That is the test whatever you do.
 
The master cylinder makes no difference, it just makes the same line pressure for both F & R circuits. It simply affects the "leg muscle" to line pressure relationship.

Posts 4 & 5 are correct. Indeed, any change to the factory design can change the ideal proportioning - bigger rear wheels, different disc pads, ... Ideally, one installs an adjustable prop valve and adjusts it by skidding on a wet parking lot as post #5. I think no factory car has that and most think like posts #3 & 6, i.e. "good enough". I don't know that anyone has compared Kelsey-Hayes disk/drum w/ 73+ disk/drum. Probably "close enough" and certainly better than no prop valve.
 
71 Dart, converted to 73 Dart disc.
Just finished this install yesterday, works perfect (not just close enough) with drum proportioning valve and master cyl.
Even stopping on wet pavement.
 
may be fine without a prop valve if large rear tires are used.
i read somewhere it was not used on wagons because they are rear 'heavy'
....test your particular combination and you will know
 
ir3333 hints at a good point. The ideal proportioning also changes with the front to rear load distribution. Many pickup trucks have (or had) a finger that sticks down from the bed and acts on a prop valve (on rear axle I assume). With more load (bed sags down), it applies more proportioning to the rear brakes. If you are a busy mafia guy, regularly hauling more than one body in the trunk, you might need that in your car.

dusterdragracer, I'm not sure you get the point. "works perfect" doesn't mean the car stops, a correctly adjusted prop valve will skid the front tires just before the rears skid. Unless you are doing such skid tests, with an observer, usually on a wet parking lot, and tweaking the prop valve to find the limit, I don't know how you know you are at the perfect point. Of course, most people don't and "good enough" is certainly acceptable, and "perfect" is a target that always changes with all the variables mentioned.
 
It might be just me, but I want the rears to skid *just* slightly ahead of the fronts. Not the other way around. Loose front traction = loose steering control.

A drag race car's use throws a serious wrinkle in the works. With that tire combo the prop valve may actually be needed in the front circuit as with those skinny front tires it is much easier to have too much front brake than too much rear brake..
 
dusterdragracer, I'm not sure you get the point. "works perfect" doesn't mean the car stops, a correctly adjusted prop valve will skid the front tires just before the rears skid. Unless you are doing such skid tests, with an observer, usually on a wet parking lot, and tweaking the prop valve to find the limit, I don't know how you know you are at the perfect point. Of course, most people don't and "good enough" is certainly acceptable, and "perfect" is a target that always changes with all the variables mentioned.[/QUOTE]


I see you didn't read my blog closely.That is exactly what I did, the brakes "work perfect",tested on both wet and dry pavement. As I said, have done this conversion many times, my buddy has also done it many times, it works perfect without any changes to the valve, or the master cylinder, so I don't know what to tell you, it works for me.Is balanced perfect.It stops so hard it makes your head hurt, without any skidding.
It is no problem to add an adjustable portioning valve to the rear, if you are not happy with your braking, but it was not required with mine.
It may be that you are comparing manuel brakes to power brakes. Mine are manuel.
 
A drag race car's use throws a serious wrinkle in the works. With that tire combo the prop valve may actually be needed in the front circuit as with those skinny front tires it is much easier to have too much front brake than too much rear brake..[/QUOTE]


You are correct, I have a adjustable PV on my front brakes on the race car pictured. It has 4 wheel Strange disc.......17" wide rears, 4 1/2" wide fronts

The conversion set up I am describing, is on a street SB Dart, with 15" wheels all around, and slightly larger (read slightly) rear tires.
 
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