Don Terrill’s Speed-Talk

when using an adjustable proportioning valve on a drag car with all disc brakes. should the prop. valve be placed before or after a line lock for front wheels. could someone explain this one in detail and why the valve is placed where you say it should be. thanks art in NY

The prop valve should be for the rear wheels. You want your front wheels to lockup before your rear wheels.

Paul

On my car I placed the line lock before the prop valve because , the prop vale has separate outlets for right front and left front brake lines or 1 inlet and 2 outlets for front bakes.

Prop valve to the rear on mine with skinnies and 14x32 rear tires.

The prop valve should ALWAYS be placed after the master cylinder and before the rear brakes.

It is important to select the correct prop valve with respect the the slope and knee of the prop curve.
In our race cars, we place a brake pressure sensor in both front and rear brake lines. This permits the measurement of the hydraulic brake bias.

You want your front wheels to lockup before your rear wheels

I don't.

panic wrote: ↑Sun Dec 11, 2022 2:48 pm You want your front wheels to lockup before your rear wheels

I don't.

In a perfect world they would both lock at the same time, or better yet not lock at all do to effective ABS. I know the auto manufacturers wanted it that way. When we did “failed ABS testing” they wanted fronts locking first as it wold prevent poor drivers from having the rear end come around on them. We had to design the systems for the lowest common denominator of drivers.

Paul

FC-Pilot wrote: ↑Sun Dec 11, 2022 5:50 pm

panic wrote: ↑Sun Dec 11, 2022 2:48 pm You want your front wheels to lockup before your rear wheels

I don't.

In a perfect world they would both lock at the same time, or better yet not lock at all do to effective ABS. I know the auto manufacturers wanted it that way. When we did “failed ABS testing” they wanted fronts locking first as it wold prevent poor drivers from having the rear end come around on them. We had to design the systems for the lowest common denominator of drivers.

Paul

I don't want either the fronts or rears to "lock up".

I do want to control the apportionment of brake forces between front and rear. Called brake bias or balance.
The distribution of brake forces must be in response to vehicle weight transfer under braking. The harder we brake, the more weight is transfered to the fronts and less is available at the rear; the rears will lock up prematurely.

Actually, we never want lock up; we seek a predetermined amount of wheel slippage to produce maximum stopping force. The brake balance is often used to assist corner turn-in.

David Redszus wrote: ↑Mon Dec 12, 2022 8:25 pm

FC-Pilot wrote: ↑Sun Dec 11, 2022 5:50 pm

panic wrote: ↑Sun Dec 11, 2022 2:48 pm You want your front wheels to lockup before your rear wheels

I don't.

In a perfect world they would both lock at the same time, or better yet not lock at all do to effective ABS. I know the auto manufacturers wanted it that way. When we did “failed ABS testing” they wanted fronts locking first as it wold prevent poor drivers from having the rear end come around on them. We had to design the systems for the lowest common denominator of drivers.

Paul

I don't want either the fronts or rears to "lock up".

I do want to control the apportionment of brake forces between front and rear. Called brake bias or balance.
The distribution of brake forces must be in response to vehicle weight transfer under braking. The harder we brake, the more weight is transfered to the fronts and less is available at the rear; the rears will lock up prematurely.

Actually, we never want lock up; we seek a predetermined amount of wheel slippage to produce maximum stopping force. The brake balance is often used to assist corner turn-in.

Yep, that’s what we want. Unfortunately when dealing with 60 year old cars and their equally old technology, we do what we can. As the OP was talking about a prop valve, I was talking about basic 60’s technology thinking. Now if I were back on a test track working with engineers and with modern systems you bet we were making the most of the dynamic system we had at our disposal (well all except for my last employer, he had their head in the sand).

Now I am off flying planes and not having to fight with management and bean counters to build a better mouse trap.

Paul