I read several posts that say if the spring is removed from the proportioning valve the breaking performance improves. Will the rear wheels lockup easier under rain with the 36mm calipers ? How difficult is to remove the spring ?
Proportioning Valve Spring
- Thread starter Schulmann
- Start date
So I just remove that medium size spring and leave everything else inside, isn't ? That looks very simple. I would like to hear feedbacks on the handling of the car.
According to the calculations that I made the effect should be much stronger than installing 40mm calipers in the rear. I calculated 50% more force on the rear. Am I right ?
I have done also some testing. My rear right wheel locks up depending the road conditions. The tire is used and I have an alignment trouble too. I would say that with a stock viper it is better to keep the proportional valve. But with a 14'' front brake system, go for it.
According to the calculations that I made the effect should be much stronger than installing 40mm calipers in the rear. I calculated 50% more force on the rear. Am I right ?
I have done also some testing. My rear right wheel locks up depending the road conditions. The tire is used and I have an alignment trouble too. I would say that with a stock viper it is better to keep the proportional valve. But with a 14'' front brake system, go for it.
GTSnake
Enthusiast
I was told that removing the rear O-ring would rebalance the proportion to more 50/50. However after talking to JonB he said all it does is remove braking power from the front thereby making the braking system less effective overall.
I don't think you will be improving your system by removing the valve spring.
I'm planning on putting mine back to the stock configuration.
I don't think you will be improving your system by removing the valve spring.
I'm planning on putting mine back to the stock configuration.
Tom F&L GoR
Enthusiast
Schulmann, not really.
Removing the spring or cup seal allows the rear brake line pressure to rise along with the front brake line pressure. As hard as you can push, the front and rear pressures will now always be the same.
When your brake line pressure rises above the prop valve break point, you will get more braking from the rear calipers. But, as you depress the pedal even more and eventually achieve 50% higher rear brake line pressure than before, you are then also at very high front line pressure. Under those circumstances you have already locked up the front wheels. Try it; it's a small, free, worthwhile improvement, but no magic bullet.
The balance in the braking system (to totally oversimplify it) comes from having the rear calipers lock up the wheels at the same brake line pressure that the front calipers lock up the wheels because the Viper OEM brake system only has one master cylinder. If you convert to a race car system, with two master cylinders, you could achieve different brake line pressures independently, and with ABS, the system is altering the brake line pressure at each wheel (in 4 channel, in 3 channel the two rears are controlled together.)
Think of it this way: start with the brake line pressure that the fronts lock at, then use that psi and larger and larger rear piston diameters until the rears lock. Braking is due to the psi in the line times area of the piston, so if you're stuck with one master cylinder, you have one pressure in the system and can only vary piston size, piston quantity (or rotor diameter to gain the mechanical advantage.)
I admit to taking StopTech's advice for the first version. The 38mm rear caliper provides (mathematically) the same front to rear brake piston area ratio as the Stoptech front caliper (with reduced size pistons) kit. Since there was room for a bigger piston, I went to 40mm (Brembo brake seals only come in even number sizes.) It appears that the car still could use a larger size, based on those that have 40mm calipers and removed the prop vavle, and the fact that 43mm size pistons chosen for the ABS calipers (which, to controlled by ABS, would have to be slightly oversized, I would think.)
GTSnake, I think there is still a misunderstanding with what it does. Removing the spring doesn't decrease the front brake capability, it allows more work from the back brakes. If the back brakes do more work to slow you down, perhaps the fronts do a little less work. But that's different than maximum braking, when you want all four wheels to be doing as much work as they can.
Removing the spring or cup seal allows the rear brake line pressure to rise along with the front brake line pressure. As hard as you can push, the front and rear pressures will now always be the same.
When your brake line pressure rises above the prop valve break point, you will get more braking from the rear calipers. But, as you depress the pedal even more and eventually achieve 50% higher rear brake line pressure than before, you are then also at very high front line pressure. Under those circumstances you have already locked up the front wheels. Try it; it's a small, free, worthwhile improvement, but no magic bullet.
The balance in the braking system (to totally oversimplify it) comes from having the rear calipers lock up the wheels at the same brake line pressure that the front calipers lock up the wheels because the Viper OEM brake system only has one master cylinder. If you convert to a race car system, with two master cylinders, you could achieve different brake line pressures independently, and with ABS, the system is altering the brake line pressure at each wheel (in 4 channel, in 3 channel the two rears are controlled together.)
Think of it this way: start with the brake line pressure that the fronts lock at, then use that psi and larger and larger rear piston diameters until the rears lock. Braking is due to the psi in the line times area of the piston, so if you're stuck with one master cylinder, you have one pressure in the system and can only vary piston size, piston quantity (or rotor diameter to gain the mechanical advantage.)
I admit to taking StopTech's advice for the first version. The 38mm rear caliper provides (mathematically) the same front to rear brake piston area ratio as the Stoptech front caliper (with reduced size pistons) kit. Since there was room for a bigger piston, I went to 40mm (Brembo brake seals only come in even number sizes.) It appears that the car still could use a larger size, based on those that have 40mm calipers and removed the prop vavle, and the fact that 43mm size pistons chosen for the ABS calipers (which, to controlled by ABS, would have to be slightly oversized, I would think.)
GTSnake, I think there is still a misunderstanding with what it does. Removing the spring doesn't decrease the front brake capability, it allows more work from the back brakes. If the back brakes do more work to slow you down, perhaps the fronts do a little less work. But that's different than maximum braking, when you want all four wheels to be doing as much work as they can.
The proportioning valve supplies a more even braking at low pedal pressure and reduces the amount of brake force to the rears during hard braking. Removing the spring or o-ring will not detract from braking. The viper has way too much front bias, as can be demonstrated by numerous accounts of front wheel lock-up. Anyone who tracks the car has experienced the front wheel lockup.
By merely removing the spring you are not going to drastically alter the dynamics, even with Tom F&L's 40mm kit and the spring removed you will still have front wheel bias, but, no where near the oem level. If you are now locking up the rear wheels you have either suspension, brake or tire problems. You really should send Tom an email.
By merely removing the spring you are not going to drastically alter the dynamics, even with Tom F&L's 40mm kit and the spring removed you will still have front wheel bias, but, no where near the oem level. If you are now locking up the rear wheels you have either suspension, brake or tire problems. You really should send Tom an email.
