race brake educators please step inside

I pulled the trigger on the Strange Pro/Race rear disc brake kit and proportioning valve for the Duster. I have Wilwood four piston calipers in the front and have killed two sets of rotors and recently after hitting them hard at Famoso a few weeks in the final things got a bit hairy. It's been obvious to me that the fronts have been doing most of the work the last few years (to much imho). I know that the front should be biased more, but I find about every track I go to I'm using the last turnoff. Keep in mind we're only trapping at 140 + or - a couple mph. The car currently has a 15/16 master and only what I believe is a distribution block after that before the calipers/wheel cylinders. Any tips on where to set the proportioning valve, or test tools to aid in the adjustment would be appreciated.

forgot to add.. currently running stock 70 drum set up.

Tire sizes? What master cylinder?

Get any factory blocks, valves, or whatever off of it while you're doing the work.

Compare the piston sizes of the Wilwood vs. the Strange calipers. Not all 4 piston units are made the same.

That 15/16 MC may work depending on the bore size of the Wilwood calipers. But I would expect it to have to go up in size a bit. How was the pedal with the drums? Expect the pedal travel to increase with those Strange calipers using the same MC.

What kind of prop valve... also.. the bigger
the master cyl.. the less travel you get( the
pedal gets real hard)you might need a smaller
master so it travels more and brakes harder...
anything.. if your running large tires on the
rear you need more braking in the rear so the
rear tires are working harder.. just dont let
the tires skid at all.. I'm going to reduce the
master on my Rampage 1 size to get a better
pedal.. it stops fine but I have to press the
pedal to hard.... tell me your total package
that you have

front tires are 26", slicks are 29x10.5. The master is an aluminum mopar style. I'll have to do some research on the wilwoods presently on the front to get the piston size. Present pedal with the drums adjusted up was pretty soft, but I liked it that way as it wouldn't "hit" so hard during the stripe games.... or so I thought. You're saying remove the "blocks"... the only block I've seen is for the rear drums and all it appears to do is split the fluid from the line coming from the master.

Car doesn't appear to have a proportioning valve on it. IIRC it was a 4 corner drum set up originally, but we swapped it over to a 73 front disc set up long ago before finally going to the wilwoods when we did the tube K. Got the feeling it's going to be "all new" by the time I get this done. Just another things that got added to and changed over the years.

Sounds like you need 2 things... 1 size
smaller master(it will allow a bit more
travel and apply the brakes harder.. but
put on a adjustable prop valve.. that will
let you balance the front to rear better

Heres some reading for you
http://www.markwilliams.com/braketech.aspx

thanks guys... went out and peaked a little more, definitely no proportioning valve. front line single line to the rear "T" and the rear line at master goes to the line lock and then to a "T" and on to the front calipers. Ordered a proportioning valve with the brake order as I was "kinda/sorta" sure I'd need it. will probably see how things go with the 15/16 master. I had a larger one on the Mirada (also manual brakes disc/drum and it was rock hard with no feel what so ever. Really liked how this 15/16 acted so far, but if I need to change, we'll do it!

"When any four piston caliper is used with drum brakes on the rear, a pressure reducing valve must be installed for front pressure control. Because of the small front tire contact area compared to the rear large slick contact area, the rear brakes must absorb more of the stopping energy than the front (contrary to a normal street car)."

... this in a nutshell will explain warping 2 sets of Wilwood rotors.

Hi Jay. I had the same problem.

I changed to 4 piston Wilwoods on the rear with no prop valve. I also have a 15/16 master cyl. Calipers have the same bore size front and rear now.

Things are much happier now, but I'm not fast like you and never play stripe games.

You won't know what is really going on until you get a pressure gauge so you can see what the line pressure is. Just like guessing what your oil pressure is by looking at the bearings.

Get a pressure gauge so you can measure the pressure in the front line and the rear line. Once you know what the pressure is you can figure out what each end is doing when you stop. There are all kinds of reasons why the brakes aren't working properly. Could be a smashed line, something out of adjustment, a blown seal, etc.

with Andy. It might be as simple as switching the lines coming from the master.

In the reading on P's link to MW I read about the gauge deal.... looks like that would be the way to get things set up rather than figuring it out in the shutdown area so to speak.

I use these for checking brake pressure at the caliper or wheel cylinder
reasonable price, and really takes the guess work out.

https://www.summitracing.com/parts/ssb-a...ASABEgL5wfD_BwE

I would expect that if you take 2 1" wheel cylinders off and replace them with 2 calipers with 4 1.75 pistons each, there would need to be an increase in volume (larger bore MC) needed, especially if you had a soft/long travel pedal with the drums.

On a Strange Mopar style MC, the port nearest the pushrod is the higher volume outlet and is typically used for the rear calipers on a typical - big rear tire, small front tire - drag car. A larger bore MC will make the pedal "tighter" or have less travel. It will also reduce pressure at the wheels, causing you to have to use more pressure on the pedal. Bore size and getting the tubing hooked up to the correct port, determines how the brake pedal feels. Safety and personal preference are the issues.

I've never had to use a valve to reduce pressure to one end or the other on a properly set up system. Yes, sometimes you don't get the perfect MC on it the first time.

Valves, switches and any other OE "stuff" in the brake plumbing should be removed when going to the race/aftermarket stuff.

I just put the Street Wilwood front brakes on my duster, but have Drums in the rear...I'm using the stock P.valve right now, have not drove it yet (maybe someday!) so is this going to work correctly you guys think?
Brian

How big are your rear tires

front tires are 26", slicks are 29x10.5.

I assume you mean front runners and a bias slick
or drag radial