Brake Help-Drag Racing

[Aerosmith]

I'm putting a Strange master cyl(manual) and Wilwood 4 piston front brake kit on my 82 Camaro, it already has a 9" Moser with the 11" drums in the rear. I run 275/15 drag radials rear(9" slicks at the track) and 165/15 skinnies on the front. The master cylinder has a larger volume in the rear chamber than in the front. Does anyone know if the drums or discs require the additional volume? I have looked at every tech chart in Strange, Wilwood, Mark Williams, and others and cannot find anything on this.

Also, Mark Williams recommends an adj proportioning valve on the front brakes when running skinnies up front to put more braking to the larger rear tires, anyone know if it makes a difference whether the line lock is before or after the prop valve in the system?

Last, stock line size to drum brakes is 1/4", should I keep the stock size or go down to 3/16" on the rear like the front uses?

My theory is that by virtue of the factory using the larger size line on the factory drums and the smaller on the factory discs, that the drums must need more volume and the discs less volume and more pressure. However the 4 piston calipers will have a much larger volume than the stock single piston calipers, about 270% I think so I don't know. I wouldn't think the placement of the prop valve and line lock would make a difference.

Any informed help is much appreciated!

[squeeezer]

[quote="Aerosmith"]Last, stock line size to drum brakes is 1/4", should I keep the stock size or go down to 3/16" on the rear like the front uses?




yes then it goes to a hose and splits 3/16 lines to each wheel

[squeeezer]

run the adjustable prop valve otherwise known as a holdoff valve

utill you can no longer get a lock-up condition to the rear wheels

[af2]

As per Wilwood instructions I found:
The Primary (A closest to the firewall) is to be used with the highest piston bore area. In you're case the front calipers.
The secondary(B the furthest from mounting) is to be used for the smallest (wheel cylinders) area.
An in line 10 pound residual pressure valve must be used with drum brakes(in you're case the rear)

It also states to use an adjustable proportioning valve.

If you are going to use the line lock for the burn out as most do, install it after the Pro valve.
Those stock brake lines are fine.

Hope it helps.

[clay]

Another way to look at which resivoir to use is that disc brake pistons move out as the pads wear and this takes more and more volume of fluid to keep the system filled. You can add fluid to a smaller resivoir for makeup, the larger resivoir just makes life easier. Drum brakes basically always take the same volume of fluid in the system because there is an automatic screw adjuster on the bottom of the shoes that screws out to make up for shoe wear. Theorectically the cylinder always strokes the same amount and returns to the same place. Ditto on af2 about the residual pressure valve. Brakes will work without, but you'll have to pump the pedal a time or two to get a firm pedal without it - this one I know firsthand. I did dad's truck with 3/16" line everywhere and it works fine. On my nova, I have the line lock before what they call the proportioning valve (mainly the switch that turns on the "brake" light in the dash) just because that's where it was easiest - I can't really see where it would make a difference before or after. Mine does turn the "brake" light on in the dash when the line lock is set though. Clay

[Aerosmith]

Well damn, I did not see that in the wilwood catalog anywhere, can you tell me what page, or url that is on, the primary for the larger piston bore etc?
I already bought the 10lb residual valve because I knew I would need it. I guessed right on the prop valve/line lock in my mock up. I figured the lines should stay the same but every kit I could find on any site or catalog was 3/16" for the whole system. However they were all geared towards the 4-wheel disc setup. The rear discs will come probably next year if necessary.
Thanks guys. Any more good brake info is welcome if anyone has any. The web and catalogs are full of pad, rotor and caliper tech but have virtually nothing on laying out an effective system and master cylinder sizing etc.
Because the 3rd gen F-bodies have a poor stock pedal ratio(3:1) I decided to go with the 1-1/32" bore master and will move the pushrod mount up about 1" which will give me a 4:1 pedal ratio. Hopefully this should give me the necessary 1000 psi of pressure. I'm also fabbing a bracket to support the firewall fron the strut tower. I figure these things along with an-3 lines inplace of the rubber will negate any loss of pressure through flex of the firewall or expansion of the hoses.
That makes sense about the volume staying the same for the drums clay. I always tell people that if you have to top off your m/c, you probably have worn brake pads. I'm taking out the factory combination(proportioning) valve and using the Wilwood adjustable prop valve and residual valve so I won't have a brake pressure switch anymore. The dash light doesn't tell you anything you didn't know as soon as you pushed the pedal anyway. You either have pressure or you don't. I remember hearing Boyd Coddington say the pressure switch was just one more place for the brake system to leak.

[clay]

[af2]

I will try and scan the sheet for you. I am working off a lap top since my main PC crapped on me.

Couldn't get the doc to load but found the instruction sheet on line of the one I have.

http://www.wilwood.com/PDF/ds260.pdf

Hope the thing works.

[bowty1111]

I know on four wheel disc brake's the porption valve is tied to the back brake sysytem ,most of the one's I have used will turn 10 round's I've alway's set them around 5 or 6 turn's,don't know if it is the same on a rear drum system .Correct me if I'm wrong never have used one on a drum setup.Residule valve's are comforting nothing like a firm pedal.

[Aerosmith]

Thanks a lot af2, I don't know how I didn't find that. bowty, the Mark Williams site said to start with reducing the discs by 25%, the Wilwood prop valve will reduce up to 56% so I guess roughly half way to start with.

[wagon train]

I thought you would only need a residual valve if the master cylinder was lower than the wheel cylinders.

[af2]

[Aerosmith]

af2 is right wagon train, it's because the drum brakes have return springs that pull the shoes back and can push the fluid back to the master causing you to have to pump them before application. Stock master cylinders have them built in or the vehicle will have a combination valve, what most people refer to as a proprtioning valve, which takes care of multiple jobs.

[clay]

[af2]