If you are changing to disc brakes on the rear, you probably already have discs on the front, so you may want to consider changing the master cylinders you have because you no longer have the self-energizing effect of the rear brakes. With drums you need much less pressure to actuate the rear brakes. Now the braking balance will be different, but there are several ways to adjust this balance.
One way that works, particularly if you are on a budget, is the use of an adjustable proportioning valve. This unit allows hydraulic pressure to be regulated. The proportioning valve leaves the brakes at one end of the car at the same pressure while reducing pressure at the other, so the total braking force to all four wheels is less. I have found these valves work quite well in my dirt short track cars.
A better way to achieve brake bias, however, is with the dual master cylinder setup. This has a mechanically adjustable point that can shift the leverage of one master cylinder to the other in infinitely varying increments. The adjustment feature consists of a flexible cable with a knob. When this unit is properly installed, the driver can adjust the brake bias while on the track.
Our Wilwood brake setup has 71/48-inch and 31/44-inch diameter cylinders. The smaller cylinder will put out more pressure but less volume than the larger cylinder given the same input force. These cylinders can be purchased in a variety of sizes.
Either way you go, you should have some way of controlling the brake bias to balance the handling of your car. Corner entry can be very dependent on the front-to-rear braking control.
Do The DeedSince we didn't have a starting point and we needed a 9-inch Ford housing for a future project car, we called Quick Performance in Ames, Iowa. When the truck unloaded at the Stock Car Racing shop, also known as Sleepy's Workshop, we had a complete kit. All the necessary parts were there-including nuts and bolts special to the project-to install disc brakes on the 9-inch housing.
Two new metric calipers complete with pads were in the box with the steel brackets to mate them to the housing. A pair of new brake rotors was also included. A really nice touch from Quick Performance was the fine Moser Engineering axles.
Using a stand to support the housing, we installed the axles. They must be in place to properly locate the calipers. With the axles in, the rotors must be installed and tightened to the axle.
Now the calipers can be located. The first step is to determine where around the rotor to put them. You will find a right and a left in the kit. Each caliper must be placed so that the bleeder screw is at the highest point of the caliper cylinder. We have seen a situation where the caliper was placed toward the rear of the car and too far down, which resulted in the brakes not being fully bled. We had to drill and thread new bleeders at the top.
Bolt the caliper to the weld-on brackets and trial-fit them to the axle and rotor. Due to varying axle housing sizes, the brackets may need to be trimmed to correctly fit. The depth at which the brake pad engages the rotor determines this. All of the pad must be touching the rotor. Use a 11/416-inch shim under the bolts holding the caliper to the bracket. This usually locates the pads correctly and prevents the bolts from rubbing the rotor.