Line locks, proportioning valves, plumbing, oh my!

[64nailhead]

Spring in the stock unit - it equalizes the pressure in a panic stop or hard and fast push of the pedal. The idea is to keep the rears from locking before the fronts, and being that the fronts do more than 60-70% of the braking, so that's where you need the volume.

A manual adjust proportioning valve is to control the volume of flow to the rears due to a caliper piston size (diameter) change. Obviously, a larger piston needs more fluid, yadda yadda yadda.

I can't speak for what everyone has done that works, but I've had lots of practice with swapping brakes and trying to get them to work correctly. Before I put on the oversized front calipers on my MC with a stock Exploder disc on the back I could not get the rears to do diddley squat because there wasn't enough volume because the fronts would be locked on tight and the rears wouldn't have enough volume. But my setup is odd, because I cheaped out, as always - very few run brake upgrades with a stock size front rotor.

I'm curious of 565's setup as well. I have a guess, but I'm curious how he arrived at his current setup. And he's correct, big bunches of 'go' require big bunches of 'stop'. I've documented my hair raising experiences with crappy brakes at 140 - it will make you re-think the need for reasonable braking power.

 

[-dw-]

I wouldn't recommend running without a proportioning valve. It serves a purpose.

What have I been missing since Ive done this swap 13-14yrs ago?

 

[81cutlass]

Spring in the stock unit - it equalizes the pressure in a panic stop or hard and fast push of the pedal. The idea is to keep the rears from locking before the fronts, and being that the fronts do more than 60-70% of the braking, so that's where you need the volume.

A manual adjust proportioning valve is to control the volume of flow to the rears due to a caliper piston size (diameter) change. Obviously, a larger piston needs more fluid, yadda yadda yadda.

I can't speak for what everyone has done that works, but I've had lots of practice with swapping brakes and trying to get them to work correctly. Before I put on the oversized front calipers on my MC with a stock Exploder disc on the back I could not get the rears to do diddley squat because there wasn't enough volume because the fronts would be locked on tight and the rears wouldn't have enough volume. But my setup is odd, because I cheaped out, as always - very few run brake upgrades with a stock size front rotor.

I'm curious of 565's setup as well. I have a guess, but I'm curious how he arrived at his current setup. And he's correct, big bunches of 'go' require big bunches of 'stop'. I've documented my hair raising experiences with crappy brakes at 140 - it will make you re-think the need for reasonable braking power.

So i can't remember if the G body got the Kelsey-hayes or Bendix style prop valve but they got one of them and they do the same thing. I'm 90% sure the diagram below is the G body one.

I know the internet claim is rear disks require the same pressure as the front disks, but rear drums take significantly less before they lock up. Hence the claim you need to swap to a disk/disk prop valve OR gut the factory prop valve to make rear disk swaps work.

I tried the disk/disk aftermarket prop valve at first when I went disks in the rear and still had awful rear brakes. I put the factory disk/drum prop valve back in and put a B body wagon master cylinder in and solved my lack of rear brake problem.

So what your saying is the factory prop valves have a pressure regulator in the rear that limits pressure to prevent lockup in the rear? 2000 psi front, 1500 psi rear (or whatever) I'm on board there. Regardless, it's internally set up to bias front to rear maybe 100% front 75% rear.

The wilwood aftermarket one just has a an adjustment which allows the pressure to bias more front of rear.

There is 2 issues from what I gather
#1, Jim, what you're saying is that aftermarket proportioning valves aren't actually proportioning valves, they are just needle valves. They temporarily delay pressure from getting to the rear brakes but eventually the pressure gets there.

#2 Proportioning valves need a 'signal' from the front brake pressure to reduce the rear pressure to a constant %. You can make a pressure regulating valve for the rear but if you only have 1000 psi up front and the rear is set for 1500psi, your going to get 1000 psi in the rear too and that might lock up your rear brakes in some situations.

So maybe the reason I'm initially confused is that the entire market on aftermarket prop valves has been lying this whole time?

I see 3 types of adjustable 'prop' valves

1- obviously needle valves

Compact Adjustable Proportioning Valve

www.speedwaymotors.com

2- probably pressure regulating valves

Summit Racing SUM-G3905 Summit Racing™ Adjustable Brake Proportioning Valves | Summit Racing

Free Shipping - Summit Racing™ Adjustable Brake Proportioning Valves with qualifying orders of $109. Shop Brake Proportioning Valves and Distribution Blocks at Summit Racing.

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3-likely adjustable prop valves

Wilwood Disc Brakes 260-11179 Wilwood Brake Proportioning Valves | Summit Racing

Free Shipping - Wilwood Brake Proportioning Valves with qualifying orders of $109. Shop Brake Proportioning Valves and Distribution Blocks at Summit Racing.

www.summitracing.com

What I'm not finding is option 3 that has a single outlet that easily can connect to the line lock and then T to both front calipers.

The risk I see (besides instructions and NHRA rules) from putting the line lock between the master and prop valve is that when you release the pedal after you close the valve and pressure drops to zero in the rear lines the spool/barbell In the stock prop valve will shuttle back and trigger the brake light. Same scenario if the rear brake line blows or one of the halves of the master goes out. Does the spool re-set when you release the line lock and you tap the brakes again or do you need to go through a special process to reset it?

Running a line lock before the prop valve creates a slight risk along with replacing a prop valve with a needle or pressure regulating valve.

Is my thinking cap on right?

 

[81cutlass]

Fully functional factory proportioning valve, the brake set up was recommended by Wilwood, they said the adjustable would work better for me than a fixed disc/disc valve and they were right, also I did this 20 years ago.
As far as the line lock I don't remember exactly how it is plumbed but I followed the directions and have it mounted on the frame rail below the master cylinder.

Interesting. Surprised they didn't recommend one of their adjustable prop valves. Maybe they weren't on the market yet?

The adjustable valve (assuming it's pressure regulating) after a stock prop makes sense if your car is lock the rear brakes up happy with the stock master but I'm not sure if would allow more pressure in the rear in the case you want over the stock proportioning ratio.

 

[565bbchevy]

Interesting. Surprised they didn't recommend one of their adjustable prop valves. Maybe they weren't on the market yet?

The adjustable valve (assuming it's pressure regulating) after a stock prop makes sense if your car is lock the rear brakes up happy with the stock master but I'm not sure if would allow more pressure in the rear in the case you want over the stock proportioning ratio.

I don't think their built in adjustable prop valves were out yet, I was told to test in a big open parking to dial it in and get the rears to lock up right after the fronts to make the big sticky rears and rear disc do a lot of the work without over powering the front skinny tires, I got it set to where it works perfectly.
I think back then we used a video camera and I had white stripes painted on my tires.
The only time I ever had an issue was when I went to work with some old BFG drag radials to burn them up and then after getting on it when I went to stop the rears locked up and skidded because the tires were so hard.

 

[64nailhead]

I believe the Wilwood that you linked above is a true proportioning valve. I say that because it's creating proportion between the front and rears based on individual axle bias - I believe.

The Summit adjustable one that you linked is more of a way to either limit the volume to the rears which also creates additional pressure between the factory prop valve and adjustable valve to maintain proper bias between the fronts and rears.

I'll go out on a limb and say that they way 565 has described his setup is the correct way to use it. I've never installed one like that, but it makes the most sense of the different types of valves.

The Wilwood unit looks to be an excellent option as well for a fresh install.

 

[bracketchev1221]

On the race car, I had the line lock right off the master to an adjustable proportioning valve on the front brakes to keep the fronts from locking up under braking at high speed. Ran the car for 20 years that way. Ran 6 different tracks and passed tech at every one of them. Mine was a disk/drum setup so I wanted to rely on the rears more with the little front tires.