In our classic cars, maintenance is something we all must do. Generally, that involves a Saturday morning where we jack the car up and grab a handful of tools to perform some form of a task on the car. Or it could be a bottle of polish followed by some elbow grease. Either way, the work usually involves effort and sweat. If you are driving a classic car that has a disc brake conversion on the rear using a single piston GM caliper, there is a maintenance item that you can do that doesn’t require any tools or sweat and very little effort! What am I talking about? We are going to get you into the habit of using the emergency brake and call it maintenance. This isn’t going to necessarily be every time you park - but more often than I bet you use it now. From our experience in the classic / hot rod industry, we have seen many cases where people almost never use their emergency brake. In fact, some folks don’t even have the emergency brake connected.
One of the most common aftermarket calipers used on classic cars and hotrod builds is also a key component in many rear drum to disc brake conversion kits (including some of the rear systems that we sell) is based on General Motors' design. It is a very good caliper that works for many different applications. As we have previously described in a TechTalk article detailing how to adjust these brake calipers, part of the functionality of the emergency brake is to continuously readjust the rear brake calipers based on pad wear. As your car's brake pads wear and friction material is removed, the pads are further away from the rotor surface.
GM designed calipers use a “sprag” inside the caliper piston. The sprag is essentially a clutch that applies torque in only one direction - like a ratchet. When the parking brake is applied, the sprag is activated if there is 0.030” or more clearance between the rotor and friction material on the brake pad. If the clearance distance is 0.030” or greater, the sprag revolves inside the piston moving the calipers outward and keeping the rear brakes properly adjusted. It is likewise critical to have the calipers adjusted correctly to begin with. Again, click here for a link to the article on adjusting rear brake calipers.
Of course as always, inquiring minds want to know: “what happens if this advice is not followed and you don’t adjust the calipers to begin with or you don’t use the emergency brakes?” Well, here are 2 likely bad outcomes:
Scenario #1 – You will start to lose service in the brakes because the caliper piston is traveling further to reach the brake rotors. If this happens, the brake pedal will feel very soft. This happens over time and is never really noticed until that one time when you really need the brakes and they aren’t there for you.
Scenario #2 – The sprag can seize inside the piston and possibly stop working. If the piston seizes and the sprag doesn’t work, you could be operating strictly on the front brakes. That is a scenario that none of us want.
For whatever reason, it can be difficult to remember to activate your emergency brake. Most of us have developed a "park and walk away" mentality when driving our classic car or even our daily driver. However, one of the best things you can do maintain full functionality for brakes with this type of rear caliper is get into the habit of using the emergency brake when you park. You’ll be benefitting your car and performing a bit of maintenance all while being a little safer as well.