How the Pedal Feels From the Driver's
Point of View is a Good Indication of
What's Happening in Your Brake System
By Jerry Slattery
We occasionally overhear conversations at street rod events such as: "How does your brake system work?" "What kind of components did you use?" "Well, mine doesn't do that, but I feel this when I push on the pedal." The pedal is a good indicator, especially to the well-trained foot of a seasoned brakeman. In this story, we uncover what these subtle indications mean and what steps you can take to improve your rod's stopping ability. The street rod industry is making some good kits these days, many based on stock applications that work and give you parts availability just about everywhere.
All these question-and-answer sessions are really clearing up some of the mystique about brake theory. To simplify the hydraulic brake system and answer some basic questions about how the system feels when you step on the brake pedal, we went to Vince Bunting, owner of C.H. Topping in Long Beach, California, a full-service performance brake shop, with inventory, counter books and plenty of hands-on experience.
The brake system is really a hydraulic system that makes pressure and moves fluid. In a street rod, there are a lot of ways to achieve this. The different bore diameters of master cylinders, calipers, wheel cylinders, pedal ratio and booster diameter really determine the amount of braking force created by the brake system. Changing these bore diameters can increase or decrease the amount of pressure output.
Dialing in your brake system means making subtle changes, although the real problem for street rod builders is that there is not enough room to use the largest diameter booster that is really needed to produce the maximum amount of pressure. Consequently, all street rod builders are trying to make the most pressure in the least amount of space. Street rods are really under-boosted, which is why in this story we are trying to get the most out of what we have on the cars (providing we are using the correct components). In most street rods there just isn't enough space for big boosters, so we have to "tweak" a little here and there to get the most out of our brake systems.
Using your rod as a baseline for how improvements or what component well it stops, these bottom-line brake replacements to make. SRR facts should give you a good idea of where and how to make stopping
Brake System Design Tips
Money will probably tell this story! The builder with the fat checkbook will probabl buy his components from the best street rod brake source. Whether you have "cubic bucks," or can only afford a donor car to help build your rod, the information here will give you a good idea of how to approach your first brake system.
If you have limited experience with brake systems and are trying to put your first one together, the least you could do is use the components from an American passenger car. We recommend a Ford or Chevy (mid-'70s on up) with weight similar to your rod. The '77-'88 mid-size GM passenger cars had 10-1/2-inch-diameter rotors and rear drums, while the full-size Camaros had 11-inch-diameter front disc brakes and some with rear discs.
First, you'll need to weigh (at a public truck scale) a rod of the same vintage and with the same components as you're going to build. Let's say, for example, it's a '34 Ford three-window coupe that weighs 2,960 Ibs. While you're at the truck scale, weigh just the front and then just the rear. Let's imagine the rod has a 302 V-8, C-6 trans and Ford 9inch rearend. The front weighs 1,568 Ibs (or 53 percent) and the rear weighs 1,391 Ibs (or 47 percent). A small motor will give these kinds of (almost balanced) figures. To generalize, most rods will fall into the 2,500-3,500-lb weight category. Imagine your new dream rod will have four-wheel disc brakes with 25- or 26-inch-diameter front tires with 67 inches of tread width. This rod can use 11-inch front rotors, non-floating or floating single-piston (GM type) caiipers having a piston bore diameter of 2-3/8 inches, or Wilwood (non-floating) four-piston calipers using 1-3/4-inch bore diameters. The rear of the rod with 28-inch-diameter tires and 8-9 inches of tread will finish our scenario. Ideally, the rear single-piston floating calipers can have the same diameter pistons (or smaller is okay, too) as the fronts and use 11-inch rotors. Or, you can use the 10- or 11-inch-diameter rear drum brakes. The master cylinder and booster from your donor's brake system would be ideal to use in your rod.
Depending on the make and model of your donor, it will probably have a power booster about 8-10 inches in diameter and a master cylinder bore diameter of between 1 and 1-1/8 inches. You can also use the combination valve under the master cylinder It includes a metering valve, proportioning valve for disc/drum systems. Your pedal ratio should be at least 5:1, but measure the pedal arm in your donor car This will give you an idea of what the factory engineers were designing safely.
The problem in street rods starts here. Most street rod builders won't have room under the chassis for anything bigger than a 7-inch-diameter booster (because most framerails are 6-7 inches high), when in reality they should use the larger diameter booster. There just isn't enough room under the chassis unless it hangs down or sticks up through the floor somehow. And, the firewall seems to be "sacred ground" when it comes to mounting the larger diameter booster, in the only place where there is room for 9-, 10- or 1 2-inch-diameter boosters. At least you know what the ideal factory-engineered scenario should be. Try to stick with it. Using a booster too small (7-inch diameter) for the factory-designed systems that used 8-, 10- and 1 2-inch-diameter boosters means you'll be trying to compensate somewhere to get the most pressure to the rotors and drums. This is what we are trying to help you understand—how to tweak your brake system to get as much pressure as possiblel The more you know about brake systems, the better you'll understand where the problems lie.
Always consult an experienced performance street rod brakeman if you're not sure or just need advice. If you call C.H. Topping and ask advice from Vince Bunting, you'll find out about their remote-mounted, large-diameter booster/master cylinder that uses your current brake system as the slave cylinder to operate the much more powerful booster and the correct master cylinder for your system. This system is one of the latest advancements in street rod brakingl