Adjustable Proportioning Valve

[ab65cpe]

Hello Everyone, What do I have to do to get the correct adjustment. Now when I depress the brake pedal, the fronts lock and the rears continue to spin (on a gravel road). I assume I need more braking at the rear. Thanks. ( '65 V8 Auto Conv w/front discs and rear drums)

[supershifter2]

adjust till the rears lock up and then back off the rears so they dont lock up. you dont want the rears to ever lockup.

[22GT]

No. You're done. You want the fronts to lock first. If the rears lock first, the back swings around and becomes the front, and you go backward off the road.

[66sprint200]

I agree, the fronts should lock up first. Will the rear end swing around while the rear tires are locked up & the front wheels are not ? Seems strange that locked up tires will "pass" tires not locked up. Obviously, you will loose control regardless w/ either front or rear locking up. Dean

[JohnnyK]

No, if it were me, I'd do it until the fronts lock up and the rears just barely do (after the fronts, of course, if it's possible.. Might be so you can't get the rear to lock up without doing it first.. Haven't played with mine enough.

[supershifter2]

when you lock up the rears the back end wants to fishtail. i cannot explain the reason for this but when you lock up the rears and not the front you can spin out. a 180 degree turn is done by using the parking brake to lock up the rear wheels and turing the steering wheel about a 1/4 turn. i love do 180's especially on wet pavement at night when no cars are on the road.

[Arya]

Originally Posted by supershifter2

when you lock up the rears the back end wants to fishtail. i cannot explain the reason for this but when you lock up the rears and not the front you can spin out. a 180 degree turn is done by using the parking brake to lock up the rear wheels and turing the steering wheel about a 1/4 turn. i love do 180's especially on wet pavement at night when no cars are on the road.

Weight shift, momentum, car's geometry.

You definitely want more to the front.

[66sprint200]

Thanks for explaining about the fishtailing guys. Dean

[64.25]

I also think you should adjust so there's more rear braking- what I did was adjust until the rears started to lock first and then back off some (instructions should come with the valve as to how much- 1 turn ...). True you don't want the rears to ever lock first but you also want them to do some work. John

[wareagle]

Originally Posted by 66sprint200

I agree, the fronts should lock up first. Will the rear end swing around while the rear tires are locked up & the front wheels are not ? Seems strange that locked up tires will "pass" tires not locked up. Obviously, you will loose control regardless w/ either front or rear locking up. Dean

OT, but noticed your picture. I used to live about 2 miles from Elvis' birthplace in Tupelo. When were you there?

[Renegade600]

Usually you want to adjust until the rears start to lock, then back off on the rear slightly.
This will keep the majority of the stopping on the front, but in a panic, all will have stopping. You do not want so much the rear skids in the rain, but you also want the back brakes functional.

This is the way I've set up all the hot rods I've built, and they have all stopped straight and true.
Tom

[caveeagle]

Seems strange that locked up tires will "pass" tires not locked up. Obviously, you will loose control regardless w/ either front or rear locking up. Dean

I know it seems counter-intuitive, but a 'locked-up' skidding tire will have less resistance (especially laterally), than a tire that has good traction with the ground.

This is why semi-trailers will tend to jack-knife when they lock up the rear trailer brakes. Anyone with a lot of experience driving large trucks has probably experienced this at some point. It is actually a very creeping feeling when you lock up the rear brakes on a large truck. You can actually sort of 'feel' it. And then you can see the trailer start to swing around in your mirrors. Hopefully you notice fast enough, get off the brakes and the trailer will fall back in line behind the tractor.

Same concept with our cars. Just a lot less dangerous.

[ScotiaFE]

The best way to set the brake bias is with a gauge on the front and back.
It's a bit of work, but a lot of piece of mind.
1200 psi on the front and 800 psi on the rear should work great for you.
You want the front about 15 to 20 precent more than the rear.
This is a great kit, but you need two kits to do it correctly.

http://www.summitracing.com/parts/ssb-a1704

[Fullbasement]

Originally Posted by 66sprint200

Seems strange that locked up tires will "pass" tires not locked up.

You're just thinking too straight forward literally.

Think of it this way. Rainy day, you're coming around a tight turn and you suddenly have to brake. Of course you don't want anything to lock up. But if the rears are way ahead of the fronts, then they will give up traction and want to swing out. And the fact that the front has the majority of the weight due to the engine etc. makes that light rear end want to pivot around the center of that weight.

Now if the fronts lock it's no fun either, but those front brakes will be much more effective because of the weight of the engine adding to the tire traction.

[supershifter2]

Originally Posted by 64.25

I also think you should adjust so there's more rear braking- what I did was adjust until the rears started to lock first and then back off some (instructions should come with the valve as to how much- 1 turn ...). True you don't want the rears to ever lock first but you also want them to do some work. John

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