In almost every instance, bigger is always going to be better when selecting the best options for your disc brake conversion system for your classic car. Most everything from the size of the brake rotors all the way to the power brake booster is a situation where bigger is better. Let’s take a look at those components and explain what we mean by that statement.
First, let’s look at the most visible part in a disc brake conversion kit and that is the brake rotor. There is obviously a limitation when it comes to the brake rotor and that is the wheels being used on the vehicle. The best thought that can be taken here is to choose the biggest brake rotor that will fit in the wheel but stays within your desired budget. We understand that there are some really big options out there but they might be crazy priced for your particular situation. That said, we also have to remember that the bigger wheels that would allow that 15” rotor should get a bigger rotor and brake package. This is not coming from a looks standpoint but from the standpoint of how much more work the bigger wheels is requiring of the brake system. It takes more distance to stop a vehicle as you increase the wheel and tire size. You should have a brake system that addresses that.
On the other hand, there are times when people are trying to keep a smaller wheel due to it being the original wheel and tire package for the vehicle. We understand that but also offer a bit of a warning. There are companies that are selling disc brake conversion kits that actually use a rotor package that is actually small enough to fit within a stock 14” wheel. To do this, however, they must go backward in rotor size. Some going all the way down to a ten-inch rotor. This is simply not smart and truthfully, you should keep your drum brakes at this point. Think about what you are doing and then compare it to what you see on the road. There was never an engineer for any of the car manufacturers that took a 4,000-pound vehicle and designed a brake package that small. They wouldn’t do it and you shouldn’t want to do that to your vehicle either.
Power Brake Boosters
The other main component in a brake system that you have choices on usually is the power brake booster. Obviously, this is only if you have chosen to convert to a system with that Power option. The power brake booster is the component that uses engine vacuum to help aid in the application of the brake pedal and the feeling that comes from that application. Too small a booster for the vehicle and the pedal will feel hard. Therefore, always use a booster that is maximized in size to the space available. If an 8” booster will fit without any trouble but a 9” booster will fit with just a tad bit more work or inconvenience later, go with the larger booster. You will enjoy driving the vehicle so much more.
The only time that choosing the larger booster won’t be the case is when the car is staying four-wheel drum brakes. In this case, a little more care has to be taken as too much size in the booster can actually cause a brake pedal that has a very touchy and sensitive feel to it. This will make the car an absolute handful to drive and nobody wants that.
The only area to avoid the bigger is better scenario is in the master cylinder. As you know, the choices in master cylinder bore can typically range anywhere between 3/4” and 1-1/4” in size. Going with the larger 1-1/4” bore would be the right thing to do in our bigger is better scenario but the master cylinder and the bore size are something that must be looked at more closely based on the rest of the brake system. The bore size needs to match the rest of the brake system from caliper and what type all the way to whether Power or Manual. There are many instances where the smaller bore will make the brake system perform much better than its larger counterpart. This comes from the master cylinder delivering larger volume at the larger bore size but a higher line pressure at the same effort than that of a master cylinder with a much smaller bore size.
Just like anything else in the vehicle, choosing the right components to do the job of a disc brake conversion can be a trick task. That is where we come in. We are in the weeds of this stuff every day and understand the needs of the system but also the need of the customer. Basically, we are here to help you in any way we can. Give us a call or shoot us an email.