Let’s be honest here, the only time we think about replacing our master cylinder is when the current unit isn’t working properly. With all of the technological advancements in our industry, we know that even a stock master cylinder will still move fluid and help your vehicle come to a halt. So, if a stock-type master cylinder is “good enough,” why do we need a fancy new one?
For our situation, it involved pedal effort. We recently added a Wilwood front disc brake kit to our 1964 Corvette. Considering it is a manual brake system, our pedal effort was going to be a little tougher with the disc brakes thanks to a 1-inch-diameter bore of the stock-type dual reservoir 1967 Corvette master cylinder. The 1-inch bore was fine for drum brakes, but the additional pedal effort encouraged us to seek out a 7/8-inch bore master cylinder.
Wilwood Engineering was the top choice when it came to 7/8-inch bore master cylinders. Wilwood’s tandem master cylinder is a nice-looking piece and its aluminum construction will shave a few pounds off of our modified 1964 Corvette. We also wanted an adjustable proportioning valve to match the new master cylinder, so we opted for Wilwood’s kit. We made a trip to the local parts store for an adapter fitting (front brake line to the proportioning valve) and a short piece of brake line to connect the proportioning valve to the residual pressure valve, which runs inline on the rear brake line. The swap took a few hours and the toughest tasks were dialing in the pushrod length and bench bleeding the master cylinder.
The end result is a brake system that is ready for severe action. We may never take our Corvette to the track, but it’s good to know that these parts are designed and tested for racing applications. The small bore provides the right amount of brake pedal feel with our new front disc brakes, and we always like the idea of shedding a few pounds from our car. Take a look at how we upgraded our early C2 Corvette with a new master cylinder and proportioning valve, and see if it’s the right choice for your application. Vette
1. We already upgraded our single reservoir master cylinder with a dual reservoir unit. While this master cylinder still functioned, it didn’t look great and we worried that the large bore would increase the brake pedal pressure effort with a recent disc brake upgrade.
2. Our first step is to loosen the brake lines on the bottom side of the combination valve. The short lines from the master cylinder to the combination valve can stay in place, and the entire assembly can be removed as a single unit.
3. Next, we removed the two nuts that attach the master cylinder to the firewall, using a 9/16-inch wrench.
4. Under the dash, we locate the brake pedal pushrod and clevis. Using a straight screwdriver, we pry the clip (see red arrow) over the end of the retaining pin. Then, we can remove the pin and the pushrod can be removed.
5. With all of the nuts and brake lines removed, we can remove the master cylinder and combination valve as a single unit.
6. The new Wilwood 7/8-inch aluminum master cylinder (PN 260-9439) comes with the necessary plugs, fittings and adapters to make it work with most applications. We start by installing the two supplied plugs for the right side of the master cylinder, and then the two line adapters on the left side.
7. After measuring from the mounting flange to the center of the clevis on the old master cylinder we determined that we needed a shorter pushrod. We used a Wilwood Universal Brake Pedal Pushrod Kit (PN 330-13914). The snap ring is removed and then re-installed in order to replace the pushrod.
8. Some applications may need an even shorter pushrod than the one provided in the universal kit. It is very important that the rod is short enough that the piston returns all the way to the stop.
9. After getting our pushrod length dialed in, we can install the rubber boot, and then do a final install on the clevis and jam nut.
10. All the ports on the Wilwood Adjustable Proportioning Valve kit (PN 260-13190) are 3/8-24 with an SAE inverted flare. We chose to only use one of the two ports for the front brake outlet so we plugged the other port. Also note the adapter needed to use the original style front brake line, which uses a 1/2-20 fitting.
11. Now, we can slide the new tandem aluminum master cylinder over the studs. This would be a good time to crawl under the dash and make sure that the clevis is in the proper location on the pedal.
12. Part of the Wilwood Proportioning Valve mounting kit are these spacers, which go between the master cylinder and the proportioning valve mounting bracket.
13. Unfortunately, the mounting bracket in the proportioning valve kit does not provide sufficient clearance with the firewall on C2 Corvettes with manual brakes. After mocking up the proportioning valve, we modified the bracket to get the valve farther away from the firewall.
14. With the bracket modified, we can install the master cylinder for the final time. The two original nuts hold the master cylinder, spacers and proportioning valve bracket in place.
15. The red plastic fittings and clear tubes are used for bench bleeding the master cylinder. Since the master cylinder mounts in a level position on Corvettes, we can bench bleed on the car.
16. Bench bleeding the master cylinder eliminates any air pockets in the system so that the fluid flows properly. If the master cylinder isn’t bled properly, the entire brake system suffers. We pour Wilwood Hi-Temp 570 brake fluid into the reservoirs to get it started.
17. Next, we very slowly push and release the brake pedal. Too much pressure will allow air to make its way into the plastic tubes since they are not securely fastened to the fittings. Notice the bubbles in the tube. When the bubbles are gone, you should be good to go.
18. Before we start connecting the brake lines to our new master cylinder and proportioning valve, it’s important to install a 10-psi residual pressure valve inline with the rear brake line since we are retaining our drum brakes. You will not need a residual pressure valve if you have four-wheel disc brakes.
19. Our modified proportioning valve bracket required us to tweak the provided hard lines. After the necessary bends, we got it lined up and tightened the fitting with a 3/8-inch line wrench.
20. Next, we can tighten the fitting on the master cylinder side. We repeat the process on the rear line, and then tighten the lines on the bottom side of the proportioning valve. We used a short piece of line from the parts store to connect the proportioning valve to the residual pressure valve, which ties into the original rear brake line.
21. We can top off the fluid and install the lid on the master cylinder. You must bleed your entire braking system after installing a new master cylinder, especially when installing a new proportioning valve. Always check your fluid level after bleeding the system and carefully make a test drive to check out your new components.
Photography by the Author