To bypass or not to bypass proportioning valve?

[surfingfreeman]

Hello All
Finally getting to the installation of my whoa brakes and am contemplating bypassing the rear proportioning valve, if you have any experience with AND without please chime in! Thanks and have a nice weekend
Mike

[engineerted]

Yes, do it. Did mine 6 years ago no issues. I did install an inline portioning valve at the MC for the rear brakes.

Ted

[toplessexpat]

I removed mine, and put it back in again a week later having driven on a slick road. It's a matter of personal choice - but every now and then the italians did do something that (IMHO) shouldn't be reversed

[vandor]

Instead of removing it you could disconnect the linkage and tie it so it's all the way up - then it will always be open and act like it's not there. Then drive the car for a while and see how you like it.
FWIW I have kept the compensators on all my Spiders.

[surfingfreeman]

Well put.......desperation the mother of all invention.....or something along those lines.

[Dawgme85]

Mine was leaking, so I had it bypassed recently. So far, no issues, even after some fairly spirited twisty road driving yesterday.

[Exit98]

Let’s talk a little about the brake proportioning valve.

Rear wheel lock up in a high speed panic stop situation isn’t something you want to experience. The back end will come around in an instant and you will lose all control. These early mechanical valves addressed this condition in a simple but effective manner. In a panic stop much of the weight of the car is transferred to the front wheels taking almost all the load off the rear. As the body of the car lifts up and away from the rear axle a lever attached to a spring moves the valve to restrict additional pressure to the rear brakes.

Two circumstances led to the development of these devices. On pickup trucks a means of varying the rear brake force was necessary to handle the wide disparity in rear braking power required between an empty pickup and a fully loaded one. By the 1960 pickups were no longer 45 mph hay bale haulers; they were driving at highway speeds, generally lightly loaded, and were spinning off interstates backwards at an alarming rate.

In cars the late 60’s saw the development of the improved front disc/rear drum system. The front discs were capable of handling almost 80% of the stopping power, so again, a means of controlling rear wheel lock up was essential.

Modern ABS systems now take care of this issue seamlessly. ABS is surely the single most important active safety device of the last 50 years. Modulating brake pedal effort is no longer a learned art for an experienced driver. Now we teach our kids to slam on the brake in a panic situation, expecting to hear the thump-thump of the ABS, and to steer the car away from danger.

Ferrari’s of the 60’s and early 70’s use a very similar set up to ours. I’ve seen this very same discussion about bypassing these valves on their forums.

I hope you or I never experience an extreme circumstance that would require full activation of this valve. But if you do you’ll be glad you decided not to disconnect it, it’s there for an important purpose.

[toplessexpat]

...you’ll be glad you decided not to disconnect it, it’s there for an important purpose..

x 2

[MrWampus]

Thanks for that detailed explaination Doug. I can speak from experience that a properly functioning valve does its job well. In my first spider when I was in college, I went on a joy ride down a country road. I was going WAY too fast (about 85) but I was young and still immortal at that time. Up ahead I saw an old farm truck with a boat in tow ease out of a driveway on the right side right into my lane. I slammed on the brakes and skidded to a stop a few feet behind the boat. I'm sure I fully locked the front wheels and maybe the back but the car skidded straight. I very nearly went to my own funeral with the word "Evinrude" stamped in my forehead.

I don't know how those brakes would have performed if I had tampered with them but they worked well as designed.

The old farmer just eased his truck and boat over to the right shoulder so I could pass and I went back home and changed my shorts.

[surfingfreeman]

Thanks everyone for your insights and opinions, I think I will follow csaba's suggestion and force it open and drive it a bit and see what it feels like under extreme braking situations but in a somewhat controlled environment, I see wilwood has and interesting "tuneable" valve

[So Cal Mark]

I've had my valve bypassed for about 10 years now, and anyone that has attended our canyon drives can attest to the fact that I absolutely flog my car through the mountains. I've never experienced rear lockup or anything close to it. If you've lowered your car, your valve doesn't function anyway. If you're content getting the minimum function from your rear brakes, keep the valve connected

[surfingfreeman]

Mark what about it's role in poor weather conditions?

[Curly]

Mark is spot on about the valve being rendered useless if the the car is lowered, or for that matter even just fitted with heavier front springs. The valve will only work as designed if the rest of the suspension retains the original specifications - if your car is significantly lowered or the suspension stiffened up, you might as well bypass the proportioning valve.
I've left it functioning on my Spider, even though it is slightly lower and stiffer than original, but removed it on my AC Coupe which is set up as a classic tarmac rally car. Despite it being removed and being driven at 10-tenths on on tight twisty tarmac, often in the wet, the rear brakes have never locked up unexpectedly.

[baltobernie]

... I see wilwood has and interesting "tuneable" valve

Yes, here it is installed on my Spider:



I'm running stock calipers and rotors, with Ferodo pads. Unless the vendor who sold you the big brake kit has already compensated for front/rear bias, I would think that you'd need to have a proportioning valve, either the Fiat OE or aftermarket.

Having an adjustable valve allows you to tune your individual brake system, so that with your combination of springs, brakes, pads and tires you get maximum braking force on both ends of the car.

[Kevin1]

All of the big brake kits I have seen (Whoa, Vics, 500 brakes) upgrade the fronts only. This shifts the brake bias forward. With the kits installed, would that make removing the compensator more desirable than leaving it in since the fronts are now doing even more of the braking?