I'm currently upgrading to rear disc brakes and the car has had no proportioning valve for years running a 15/16 bore Chrysler style master. I'm doing so due to the fact that I've been killing Wilwood rotors on the front after only a few events and always using the last turnouts at the tracks I attend. I'm putting a valve on the line going to the front brakes (race car only). In searching around on this there seems to be quite a difference in opinion on it's location.... Noted a few of the brake parts manufacturers recommend this. Thoughts?

I mounted my adjustable prop valve on the firewall, worked just fine. Although in an effort to clean my firewall up I'm moving it to the rear just before hose that connect the brakes from body to axle.

Proportioner goes in the front system. Large rear drag tires will over come skinny fronts. When I first used Will Woods in 93 we wiped a pair of rotors in one season. It was the pad material. That 2nd pair of rotors were good until 2016. Two different cars, same set of rotors transfered to a faster car.
Doug

Baer sells a master cylinder with the ability to mount a prop valve to the bottom of it. So in their mind it doesn't seem you can get to close to the master, they seem to know what they are doing.

I have 4 wheel Disc Wilwoods. Adjustable Prop valve on rear brakes. Set it to the middle of adjustment when I installed it years ago and have never touched it. Lots of street miles and plenty of track passes.....never a stopping issue. Brake pads look great and no abnormal wear, front or rear. The idea for rear adjustable was to have front brakes with full load from master and dial up or down the rears as needed, depending on stopping quality.

Here is the Baer master cylinder with prop valve that I'm using on my Duster project.

Never used one, never had to. Use the correct MC with the correct bore size and the bias built in, and plumbed correctly according to your combination (tire sizes, caliper sizes) and it just always works. If you use any old auto parts store master and don't know the bias, it's trial and error.

That would make for a very nice clean set up. I too just converted to wilwood discs on front and rear after 30 yrs with stock fronts and wilwood rears.

I will have to see if I need to change out my old master cylinder. If so this may be an option.

Trying to attach pic...

I mounted the proportioning valve in the rear circuit. I put some rivnuts into the subframe connector and mounted the valve so that the adjustment knob just pokes through the floor between my knees when I'm driving. And I found a rubber grommet with an ID the size of the top of the prop valve housing. I slid that into the floor sheet metal and then slid the prop valve into the ID and then bolted it to the subframe connector. I'm not sure if it is really watertight since the car never sees the rain.

baer sells this bracket.

Mine

That’s basically what I’m doing Doug.... and it will be on the front brakes.
Jay

My street car is set up like DVW is, easy to reach
BTW, don't forget to remove the residual valve from the M.C.

Jay, I'm mounting mine between the front hoop bar and the kick panel. I've moved all my lines from the engine compartment to under the dash area. Let me know if you want a picture.

DVW, Why does the valve have a front and rear in port and 2 - front and 1-rear out port?

Can, why remove the residual valve?

I have wilwood 2 psi res. Valves installed, as I have wilwood disc brakes installed
Mark

Valve has 1 in then 1 out going to the line lock. Line lock has 1 in, 2 out with 1 of them plugged as the front line T is further down.
Doug

you may want to call wildwood and check what friction rate the pads are or should be. I bought a 4 wheel disc brake kit from them a few years ago and it was eating the rear rotors, they had sent the wrong friction rate pads, changed the pads and all was good.

I do proportion valve on front brakes and line lock on rear brakes. This way I match front brake power to equal the rear with bigger tires and the line lock I hit the button 1st, hit the brakes 2nd then only the front brakes will clamp on. This I feel allows a safer burnout as I can control roll out with my brakes and not just expect to roll or possibly launch forward as soon as I let go of the line lock button.

If the M.C. is above the highest point on the brakes like a stock Mopar has then the residual valve maintains pressures on the pads not letting them retract all the way, no need for the valve on disc. in my opinion
I installed a SSBC front disc kit on my 1955 Dodge Coronet and used a later model Mopar brand aluminum dual piston M.C. for a later car that had disc brake application that I assumed that the residual valve was not there, it was and when I would push the car out of the shop into the sun the change in brake fluid temp. would make the car harder to push back, untightening the front brake line cured that when it burped fluid out of the fitting
I'm building a 1940 Ford Tudor sedan with 4 wheel disc with the M.C. mounted under the floors and I used the Wilwood 3 lbs. residual valves in both lines to avoid allowing the fluid to drain back into the M.C. over filling it and making me have to pump the brakes to stop

My master is in stock location.... no residual valves added anywhere. This wasn't a post about aesthetics, but rather the theory of valve placement. Coming from a "regular" automotive background it's easy to say that you'd want the valve on the line to regulate the rear brakes as the fronts do most of the stopping.... HOWEVER, when you put "drag race" only and skinny little front runners into the equation it changes the story somewhat. Obviously no matter the tire size, you don't want too much rear bias (good way to find yourself suddenly staring at the starting line at trap speed), but you do have a lot more meat out back with the slicks to help slow things down.

Another chapter in things you notice when you go faster.

Jay "slo-kid"

Threw it out....Neither of my cars has one....

never ever? all in know is that with Wilwood/drum combo and "nothing" I'm eating up real estate getting my junk stopped, and my 3rd set of front rotors should be here tomorrow.

The thought crossed my mind to simply install the rear discs (Strange) and see how things go, but I'll most likely throw the valve on.

where did you put your proportioning valve?

In a box on the garage shelf. Bias seems good with Wilwood 4 wheel disc on my junk. I would try it first.

Mark Williams recommends panic stopping on a slippery surface at low speed to test brake bias. Will this replicate real conditions? Don't Know. What I do know is you don't want to panic stop one day and find out the rears skid instead of the fronts, don't ask how I know. Most drag cars will skid the fronts with no valve do to tire size bias. But if all 4 skid together or the front just slightly earlier it'll stop straight.
Doug

Both cars are big tires pro-street types with Willwoods on all four corners....My chassis guy said to throw it out...So I did...That was many years ago...Sure simplifies the Line Line plumbing.

I was told also to leave it out. Strange brakes all around.

Can't say that I don't agree with the "splice just makes one more place to leak" theory

I've read the MW manifesto Doug. That was linked on another rear brake discussion quite awhile back. I "kind of" thought the rear drums should work for my deal, but like I stated earlier, since getting the W8 mill running we've been killing front rotors a lot sooner than I prefer. I was also a little leary of the "skid test" you noted, although it probably falls into the better than nothing bin.

I'm running the Wilwood 150-8850K pads

"Wilwood Smart Pad BP-10 brake pads feature a medium-friction compound with the low noise and low dust of a street performance compound, plus the increased friction characteristics of a semi-metallic race compound. They have smooth engagement, with consistent response from a flat torque curve throughout their entire effective temperature range. These pads have good low-to-middle temperature wear rates and they bed quickly and provide a fast response without excessive abrasion on vented iron rotors. They are ideal for a variety of high performance street/strip, drag race, and track-day categories using vented iron rotors. They also provide light-to-medium braking on dirt tracks, including late models, Modifieds, sportsman, and street stocks"

my new front rotors (solid, not slotted) should be here today, and I stock pads for them now (another lesson learned) so maybe we'll try it without the valve and see how it goes.

With the correct pedal ratio and master cylinder you should not need an adjustable proportioning valve. I have not had one on a car in YEARS. To include the RJ car in the garage with Carbon Brakes.

IMO the Wilwood pads are part of the issue IMO. We switched to Hawk pads and have never looked back.

I agree may/may not need one. But cheap and easy to do during the build. Not so much after its all laid out and done.
Doug

I have Wilwood Dynalite on the rears and 11" Mopar brakes on the front with a Strange "mopar style" master and mine stops smooth and easy with no drama without a valve of any kind

Gus

Setting up a brake system is actually a complex engineering problem. Many bracket racers approach it by randomly buying parts out of a catalog and then they have issues. There is a lot more stuff written on how to pick a cam than there is on how to pick a brake system which is probably a mistake.

For starters the fronts usually do twice the work of the rears so you need twice as much brake force up front as at the rear. That means the front pistons need to be twice the area of the rear pistons if the rotors are the same diameter.

If the front tire is too small to handle the brake force then you end up with a different problem. Trying to stop the car with the rear brakes is very tricky. The car is a lot more stable if most of the brake force is coming from the front tires.

Killing front rotors sounds like a pad issue to me but maybe the rotors are undersize. You might not have a brake balance problem, you might just have a component issue.

The best way to debug brake problems is to put a pressure gauge in both the front and the rear brake lines. Once you know what the pressure is in the lines then you can debug the rest of the issue. For really tricky problems you can use a heat gun or temp paint to figure out if the rotors are overheating.

Also, a disc drum type of car requires a prop valve since drum brakes are non-linear and disc brakes are linear. So you need a prop valve to "blow off" the excess pressure to the drum brakes or else they'll always lock up.

A 4 wheel disc car does not need a prop valve if the caliper piston size is correctly matched. The piston ratio front to rear depends on the weight distribution of the car as well as the height of the center of gravity. Basically what you are trying to do is to match the brake force with the weight on the wheels. So a nose heavy car needs more front brake force than a car with a 50/50 weight distribution. And a car that is jacked up in the air transfers more weight to the front during a stop than a car that is super low to the ground.

A good chassis should be around 50/50 weight distribution and low weight transfer to the front and would need 2x the brake force up front than in the rear. So the area of the front caliper pistons needs to be 2x the area of the rear caliper pistons. If you follow that forumula you should be in the ball park. You can tune it with the pad selection. If it is way off then you need to adjust the line pressure or the piston size or the rotor diameter.

It isn't black magic, just regular old engineering calculation. Randomly selecting brake parts out of a catalog won't work any better than randomly selecting pistons and camshafts will work when building an engine.

Jay the big tires go in the back.. ... I do not have a valve on my car...

Same brakes, same results.

So...some think it goes on the front, some think it goes on the rear, some are having trouble stopping their car and want to reduce braking one end or the other to fix it.

Big tires on the back, skinnies up front, you can't have the fronts doing the majority of the work. That will wreck you.

How many door cars are out there with 2 little calipers up front and 4 four piston calipers on back? They aren't out there spinning around in circles in the lights.

Which port of your MC delivers the highest volume or are they equal? You need to know.

I've seen Wilwood calipers that look like other company's parts, but the bores are substantially smaller. They will not work the same. What size are the bores of your calipers?