Proportioning Valve -Yeah or Ney

[badss540]

On an 8 sec car would you run one or not, and i see cars with them either on the rear brakes and others on the fronts,any input,thanks...

[ProPower engines]

Seems to me that this is a job for chassis man in different forum.

I do not remember the master cyl. being connected to the camshaft ect......

[Ed-vancedEngines]

Your car you drive to the grocery store needs one. I am pretty sure a faster car does too. Race cars usually do well with an adjustable valve but it has to be adjusted right. Go to Mark Williams webpage and check out his many brake technicical articles. He will tell you how to use it correctly.

Ed

[badss540]

Thanks Ed, i posted it because the first tech i talked to at wilwood said to use ut on the rear brakes, car had a hell of a time stopping. contacted wilwood again and a different tech said to the fronts only, Lamb Components said to the front also and do not use synthetic fluid. thanks again.

[Ed-vancedEngines]

http://www.markwilliams.com/braketech.aspx

[af2]

Thanks Ed, i posted it because the first tech i talked to at wilwood said to use ut on the rear brakes, car had a hell of a time stopping. contacted wilwood again and a different tech said to the fronts only, Lamb Components said to the front also and do not use synthetic fluid. thanks again.

Why the rear i'll never know? I had one for the front and took it off. A wast of money. You need the most breaking power to all wheels as far as I can see.

[David Redszus]

The amount of braking force that is needed at the front or rear is a function of the vertical load on the tires. Under hard braking, weight is transfered towards the front and from the rear wheels. This would require less rear braking force as weight is transfered forward.

But if the hydraulic ratios are wrong, meaning the master cylinders/caliper pistons/wheel cylinders are not sized properly, the braking forces can be out of balance.

Properly balanced, you should be able to lock up all four wheels at the same time. The amount of brake force necessary to accomplish this task will be determined by vehicle static weight, weight transfer, and tire grip.

[Speedbump]

Exactly correct as said by David. Most factory systems use a combination valve that contains a metering function to apply pressure first to the rear to help contain the "nose dive" effect. The combination valve also proportions pressure front to rear for the change in tire loading and prevent premature rear lock up. The proportioning function was way more critical on a disc front/ drum rear set up since the drums use the hydraulic pressure AND servo action to do the job. It is less critical on 4 wheel disc setups. I would think most applications would need the proportioning valve on the rear since the normal stopping dynamic unloads the rear tires causing skid and loss of control.

[David Redszus]

It would be very hard to imagine an application that would call for a pressure regulator to be inserted in the front brake system.

A drum brake system does indeed have a servo function acting on the leading shoes and an anti-servo function acting on the trailing shoes. This must be included in the hydraulic ratio calculations as well as the friction material Mu values.

The selection of the correct pressure regulator is very important since the knee of the regulation curve will determine at what pressure it will function. Lever type regulators are hopelessly inaccurate and inconsistent. Knob type regulators are somewhat better. Always use brake line pressure sensors to determine how the regulator is functioning, if at all.

[xenginebuilder]

While I agree with the above observations about brake balance, my own experience with drag cars in particular is that you have some unique conditions which may require proportioning at either end. The original post:

On an 8 sec car would you run one or not, and i see cars with them either on the rear brakes and others on the fronts,any input,thanks...

At 150+ mph, even though the braking would be concentrated to the front, if the front brakes were adequate, the tire patch available is not going to be enough to stop the car without skidding. A mounted 14.5-32 tire and wheel has a lot of mass and leverage at that speed, and needs a certain amount of rear brake just to overcome that before the brakes can contribute to stopping. You have mass at the front and traction at the back. You might need to proportion either end depending on the mix of tire, brake caliper diameter and pistons, chute or no chute. Skidding the tires at all at either end can lead to a big problem. With some laps on the car, if you can't get it to stop properly with a small amount of proportioning, upgrade or change the braking at which ever end of the car needs it to mechanically balance the system to your particular vehicle.

[af2]

While I agree with the above observations about brake balance, my own experience with drag cars in particular is that you have some unique conditions which may require proportioning at either end. The original post:

On an 8 sec car would you run one or not, and i see cars with them either on the rear brakes and others on the fronts,any input,thanks...

At 150+ mph, even though the braking would be concentrated to the front, if the front brakes were adequate, the tire patch available is not going to be enough to stop the car without skidding. A mounted 14.5-32 tire and wheel has a lot of mass and leverage at that speed, and needs a certain amount of rear brake just to overcome that before the brakes can contribute to stopping. You have mass at the front and traction at the back. You might need to proportion either end depending on the mix of tire, brake caliper diameter and pistons, chute or no chute. Skidding the tires at all at either end can lead to a big problem. With some laps on the car, if you can't get it to stop properly with a small amount of proportioning, upgrade or change the braking at which ever end of the car needs it to mechanically balance the system to your particular vehicle.

That is the best way to sum it up!

[David Redszus]

If you have the weight on front and rear axles, vehicle weight, wheelbase length, and center of gravity height, the proper brake forces and brake bias can be easily calculated for any car.

Vertical loading not tire size will determine maximum braking force. Tire size will determine how long the tire will last.

[badss540]

Thanks for All the advice and respones, after talking to brake tech experts in this field (lamb, etc) I did it with the proportion to the front, I tested the car for the first time this past weekend, 1/8th mile track and started of slow and easy, no problems stopping from the get-go. last 3 passes (not yet full throttle and tune ) but at 125-5:60 she stoped fine, next its out to Fontana to see 1/4 mile testing, again thanks.