Proportioning Valve question?

[daveybtv]

When I bought my car the previous owner had the PV plumed in to the front breaks. I just upgraded to the Baer Track4 and SS4 rear disc kit. Should I move the Adjustable PV to the rear line?

[dontlifttoshift]

Yes. On a street car the the prop valve should always be in the rear line.

[Ron Sutton]

Yes. On a street car the the prop valve should always be in the rear line.

Agree.



*Unless for some strange reason front brakes are WAY too much for the car, inducing lock up & push on hard braking & corner entry. You didn't say what kind of brakes the previous owner had on it. Maybe he upgraded the front braking too much & not the rear.

Regardless, you're putting on a more balanced system now ... and the PV should be on the rear brakes ... just like Donny said.

[daveybtv]

Thanks that's what I thought!

[Apogee]

Scary! Front brakes should always be 100% line pressure...and then adjust the rears to balance. Making the front brakes respond in a non-linear relationship with pedal effort is less than ideal and even dangerous.

Tobin
KORE3

[Ron Sutton]

Scary! Front brakes should always be 100% line pressure...and then adjust the rears to balance. Making the front brakes respond in a non-linear relationship with pedal effort is less than ideal and even dangerous.

Tobin
KORE3

I agree. But I have seem Racers that were brake rookies do it when they put too much front brake on the car & it was locking up their front tires on corner entry. They did it wrong to start with ... and corrected it wrong.

[Apogee]

Understood, and I'm not saying two wrongs can't make a psuedo-right...just not the way I would suggest going about it. It's seems ill advised to create a problem just so you can solve it in a sorta, kinda, maybe iffy way at best.

[Rod]

Understood, and I'm not saying two wrongs can't make a psuedo-right...just not the way I would suggest going about it. It's seems ill advised to create a problem just so you can solve it in a sorta, kinda, maybe iffy way at best.

ha ha ha ha!!! I built an SCCA car that had a bias adjuster front and rear along with a turning brake! man was I all wrong

[Zspoiler]

Using an adjustable proportioning on the street is bad news. Those are made for the track. I would a Brake proportioning valve for a factory 4 wheel disc of about the same weight. I also have Baer brakes on my car . I have 1979 Z-28 Camaro. And I use one from a 1980-81 Firebird. The factory has already done the work for you .Plus you have the warning light for your brakes.

[Ron Sutton]

Using an adjustable proportioning on the street is bad news. Those are made for the track.

Zspoiler ...

I'm not a big fan of proportioning valves ... even in racing. For racing, I feel they are a band aid to get the front to rear braking bias correct. When you use a proportioning valve to reduce braking to the rear ... to achieve the the proper front to rear bias ... you're doing so by reducing the rear braking & reducing total braking force.

In all of our cars, I design the brake system to be very close to the proper front to rear bias we need ... utilizing twin master cylinders and adjustable bias bars (or pedals with adjustable bias bar built in). This method is easy to dial in the optimum brake balance ... even fine tune it as track conditions change ... and it is NOT reducing total braking force. This method allows you to dial in the exact desired brake balance & keep the total braking force.

The draw back to this twin M/C & adjustable bias control option for most street cars ... is you are changing pedals & going away from the factory location dual M/C (and sometimes power booster). If a PT person wants to retain their pedals, dual master cylinder and/or power booster ... utilizing an adjustable proportioning valve is the best way to dial in optimum brake bias.

I personally wouldn't want to have a factory non-adjustable proportioning valve if I'm changing all the brakes & driving the car HARD. You're "stuck" with whatever proportioning came with the factory unit, and is highly unlikely to be optimum for your PT car with all the handling & brake changes you made. So in those situations, I think the adjustable proportioning valve is the RIGHT MOVE. Not the best method ... just the best if your sticking with a dual M/C.

Does that make sense why it's the right tool for some applications?

[Apogee]

Most OE fixed proportioning valves are very conservative for pro-touring applications, meaning the don't provide as much rear brake as the car can tolerate. That said, proportioning valves aren't a band-aid IMHO, but rather a tool that allows you to at least get close to optimizing front/rear brake bias over a range of deceleration rates, not just 100%. For a track car, tuning for 100% braking makes the most sense since you want to be on your brakes for the shortest period of time when you apply them. For a street car, you tend to use the full range of deceleration rates from 0.01 G's to 1+ G's in braking. The physics of the situation requires a non-linear front/rear brake bias, hence the use of proportioning valves which essentially use two linear relationships at different slopes to approximate what should be a curve...while not ideal, it's still better than trying to approximate a curve with one linear line. While a dual MC can be tuned to optimize braking for one deceleration rate, typically 100%, it still maintains truly a linear bias relationship front to rear thereby underutilizing the rear brakes under less the full braking.

That's enough brake theory for me...as posted by Rod, there are many ways to skin this cat, some of which fly in the face of everything we "know" to be true and yet still are made to work and work well.

Tobin
KORE3

[Ron Sutton]

That's enough brake theory for me...as posted by Rod, there are many ways to skin this cat, some of which fly in the face of everything we "know" to be true and yet still are made to work and work well.

Tobin
KORE3

Agreed.

[novaderrik]

Using an adjustable proportioning on the street is bad news. Those are made for the track. I would a Brake proportioning valve for a factory 4 wheel disc of about the same weight. I also have Baer brakes on my car . I have 1979 Z-28 Camaro. And I use one from a 1980-81 Firebird. The factory has already done the work for you .Plus you have the warning light for your brakes.

the Wilwood adjustable prop valve that i put in rear line of my 71 Nova made the car drivable- the 12" C4 Vette front brakes weren't exactly designed to complement the stock rear drums... it took a little doing, but i found the sweet spot where the car would just hunker down and stop if i mashed the brake pedal at highway speeds instead of just locking up the rears immediately.. ideal? probably not... but it's the hardest stopping and easiest to control car that i've ever driven and the adjustable prop valve was to thank for that...

[daveybtv]

I moved the PV valve to the rear line, seeing that my break set up is matched from Bear and I am using the correct bore master they recommended , should I start with the valve wide open full line pressure then back it off if it feels like too much rear break? never had one before but that makes the most sense to me?

[Ron Sutton]

Dave,

Yes, you should start with the PV wide open ... basically doing nothing. As you drive the car in a safe, controlled area ... test the brakes doing straight line braking ... increasing the braking pressure each step. Start soft, then medium, hard, harder. If at some point you are locking up the rear brakes ... dial a little rear brake pressure OUT of the system with the knob on the PV valve ... (Meaning decrease rear braking) ... and continue your testing.

What is ideal may be debatable & personal preference. For track driving, you want the front & rears to lock up together ... if they lock up. If the fronts lock up first, the car will push on corner entry. If the rear brakes lock first, the car will get loose on entry. So balancing them is both safest & fastest.

It has been a few years since I worked with adjustable PV valves ... but something is nagging me the adjustment direction is or seems backwards. I "THINK" if the knob is all the way out ... the rear braking reduction is maximum ... and all the way IN is NO rear braking reduction. But again, it's been awhile. So either find & read the instructions, ask Tobin or ask someone that uses them on a regular basis.

Best wishes.

[daveybtv]

Awesome Thanks Ron.

[Ron Sutton]

No worries. Post your testing results so everyone can learn.

[novaderrik]

just looking at a pic of a Wilwood adjustable valve on the Summit site, it says "less brake" with an arrow pointing counter clockwise on the end of the knob...

[Ron Sutton]

just looking at a pic of a Wilwood adjustable valve on the Summit site, it says "less brake" with an arrow pointing counter clockwise on the end of the knob...

Wow. Instructions right on the knob with an arrow. Even I could follow that.

[ROBS6T8]

Thank you Ron and Tobin. A very good read. : I too have a PV valve and was waiting to install the rear discs before I got all crazy with adjusting the brakes. She stops fine now but I'm thinking it's more front than rear. The new rear end will be going in shortly!
I will post my testing here.