Okay, I’ve rear several posts and now am even more confused. I really just need a simple answer for a starting point. I have a new build not running yet. 34 Ford Coupe std hot rod. Disc brake front /drum brake rear. Brakes are installed except rear e brake. Today I bled the system and have a firm pedal. I have big/little tires and a Wilwood adjustable proportioning valve. I’ve read all about test drives, hard stops and wanting the rears not to lock up before the fronts. I just need to know a good starting point before getting on the road. 1/2 way seems like not enough rear restriction to me. I am ***uming turning the knob clockwise restricts the rear braking. I was thinking about 1/4 open from full close as a starting point. Advice on where to start brake bias is greatly appreciated. Thanks
You have no way of knowing what the balance is now so you'll just have to try it and see. You will want the fronts to lock up just before the rears in a hard (panic) stop. It helps to paint a white stripe on the tires of one side and have an observer watch. You'll need to find some abandoned pavement or a very large empty parking lot.
Thanks, I just thought someone here with a similar set up could get me a starting point before I try to bed the brakes in. I still have a few things to finish before it’s on the road.
My avatar car has SBC with Super Bell "Power Stopper" disc brakes up front and 11" Ford drums in back. The Wilwood proportioning valve is set at 1 1/2 turns out from full in. This should be a good starting point for you.
Variables like, the weight of the car, (front and rear), components used in the brake system and tires, typically dictate where they're set. I start with them wide open. If the rear brakes are prone to locking up on hard braking, I close it a quarter turn at a time until they work the way I want them. The prop valve on my current heap is wide open, four wheel disc brakes work fine.
I just went through this on my A PU with disks all the way around and I started with the valve wide open ( full brake pressure to the rear and went and drove it slow and did some light stopping to see if it was way off or not and then progressed to harder and faster braking . In my case I did not need the valve and I actually need more piston area on my rear brakes so the valve was useless as I have a design issue I need to rectify . there is simply no way your going to guess and be close unless your building the same car over and over with the same pads , shoes , disks , drums , master cylinder, tires and pressure , weight distribution, suspension spring weight , shock valving and so on . even road surface will factor in f you get really serious . On my Corvette I have it about 2 turns out . With disk /drums . On new brakes your going to have to break in the shoes and pads , especially the rear shoes before you can really accurately adjust the valve because initially the rears will need to wear in unless you really have the shoes arced perfectly and even then they need to break in . That's why I start with the valve set for max on the rear . You can drag the rear brakes a bit to speed up the break in just don't get them hot . You will also know right away if you need to adjust it down if its locking up at slow speed and that saves doing as many high speed stops were your more likely to flat spot tires or worse . Also finally after you THINK you have it right after a bunch of stops recheck it after the brakes are cold like it will be in a panic stop on the street out of the blue . Unless your road racing or driving hard in turns like a sports car you want it right for the one time emergency stop were your at the edge of lock up . Brake temp affects that especially with some shoes and pads . On my old 240Z car with SBC that I auto crossed years ago I was playing with the valve a lot I could adjust from the drivers . On the street I backed it off a bit so I knew id not lock up the rears except under the most hardest braking and it would be more predictable. On the track id set it so I could get both ends stopping about the same going into turns . Most guys way over think it and on the street you just need most of the rear brakes capability and if you locking brakes up in moderately hard stopping in traffic then its to much. better less than to much that takes control away . good luck
These adjustable prop valves have some proportioning built into them already, so even backed fully out they have a small restriction. So you really need to back it all the way out and then find an empty parking lot to do test stops. But you might discover you can leave it fully open, or begin turning it down until the rears don't lock up. On my current '39 Chev with discs up front and Explorer 8.8" drums in the back I found the prop valve restricted too much even wide open. I plumbed the rear line to eliminate the adjustable prop valve and my brakes worked perfectly!
You have apples and apples. He's dealing with apples and oranges. Your master cylinder also comes into play. Most of the dual master cylinders for modern cars are sized for the system of the car you got it from. Drum/drum disc/drum disc/disc. A lot of the disc master cyls also have built in residual valves. Our T is an apples/apples car but the Pvalve is turned in a couple turns to balance it out - baby Wilwood front calipers and skinny tires VS fat tires and big Hurst/Airheart NASCAR calipers in the rear.
^ I read what he wrote and you obviously read what I wrote, so I'm confused about the point you're trying to make.
Ok, first, thanks to everyone for the help. I read and found them all helpful. I should have been putting out more detail up front. The car is a Downs 3 window 34 highboy. SBC/350 automatic. Rear end/brakes are 9 inch Ford with drums. Front discs are Wilwood D52 4 piston calipers. Master cylinder is GM Corvette style but not sure it is from a Corvette. I put residual valves in line since m/c is mounted under the floor. The Wilwood adjustable proportioning valve is inline rear brakes and m/c. Tires are front/ 155-80-15 and rear are 285-60-16. Tire size huge difference was my initial concern. I looked at Wilwood on line tech support and there is lots of good information there but unfortunately not the answer to my question. I will call their tech support tomorrow and report back with what they say. Again, thanks to all for the help.
I used 100's of the Willwood adjustable Prop valves along with the blue and red residual valves. I always included the prop vslve instructions. I always wondered how many of my ch***is customers actually adjusted the valve or just let it as it came? My favorite is still 4 wheel drums with a MC with built in residual valves and no prop valve easy and they work good.
Now that’s embarr***ing, I thought there were no instructions, but it was a long time ago when I bought it. (the car has been in paint jail). Maybe I better go back out in the garage and look around.
My truck weight is split 50/50 front and back, under a hard 40 mph stop it will just start to leave black marks at the rear tires. My valve is turned few turns in, not rear sure how many, I just kept hard stopping and adjusting till I knew what it would do under a panic stop. I still check it every so often, in my area, drivers just don't give a sh!& about any other car on the road but their own.
I found it useful to use some light gravel covered road to adjust the valve, it's easier to read the gravel than trying to use pavement. I normally bleed the brakes with the valve wide open so there's no fluid restrictions, then go skid it in the gravel to see what's locking up first and adjust accordingly.
Turning clockwise/screwing in increases the maximum allowable pressure to the rear wheels. You need to unscrew counterclockwise to reduce rear braking. It’s basically a spring and limiting valve so the more you compress the spring the higher the line pressure will be at the cut off point.
Turning the knob clockwise will increase pressure to the rears, per the instructions from Wilwood. I started with (and recommend) the valves fully clockwise (maximum rear pressure) on my front disc/10" Bendix rear drum hotrods to quickly determine rear brake performance as over or under braking. Hard braking with the '32 resulted in "lazy" rears, so larger wheel cylinders corrected that issue, while leaving the valve fully CW. The '40 rears were a little aggressive, so a couple turns CCW resulted in very good F/R balance without a wheel cylinder change. Note-The brakes should be adjusted correctly and burnished or bedded before any balance evaluation is performed. Normally, green discs can be down on effectiveness and shoes may be up, but can reverse when burnished.
Since I have my master cylinder placed sideways behind the dash and the brake lines were inside the cab, I mounted the adjustable prop valve under the dash so that I could easily play with it. I've never adjusted it. Seems to work fine,
Great information here. Much appreciated and thanks to all. I contacted Wilwood tech support. They recommended starting out full counterclockwise (they call this fully proportioned) Next, do the test drives at moderate speed and stopping to bed the brakes in. After you smell brake lining your good. Then start proportioning a turn or so st a time until you achieve desired bias. Soooo there it is, straight from the horses mouth as they say. I greatly appreciate all the help. (still didn’t find the instructions)
Just keep in mind the fully CCW valve setting allows 100 master cylinder psi initially to the rears plus 57% of all additional M/C psi going to the fronts. The results may over work the fronts while under working the rears during burnish, and is why I start burnishing and any balance testing with the valve full CW., but that's my opinion.
That makes sense too, maybe I’ve come full circle and back to starting in the middle. I’ve still got time to ponder it as I’m currently building a battery mounting tray. Thanks
The Jalopy Journal
