On this week’s show there’s a question about a car w/disc brakes on front and drums on the rear. That’s how all my cars have been configured. Disc front, drum rear. Ray suggested one way to tell if the caller’s problem was in front or the rear was to use the parking brake to stop the car as an experiment. If the problem remained, it was probably the rear brakes. It made sense, as I understand how the parking brake works with rear drum brakes. But listening to the call, I realized that I have no idea how the parking brake works when the car is configured with rear disc brakes. It seems like it’s a more complicated problem to connect a cable to control disc brake calipers. Anyone offer a brief tutorial?
Depends on the car. Some rear disc brakes have a mechanism built into the caliper that pushes the piston out ever so slightly to make the pads squeeze the rotor. Some cars have an entirely separate system, that uses the center “hat” of the rotor like a brake drum with little shoes inside that are actuated like a classic drum brake setup.
asemaster has pretty much said it all. With the system built into the caliper the driver needed to use the park brake on a regular basis to keep the rear brakes in adjustment since the p/b calipers did not automatically adjust like normal calipers.
The top hat design has been used for some time as I have seen them on older vettes and Volvos.
Yes, my Dodge has the drum-in-hat arrangement. That means that I don’t have only four sets of brake pads for the discs, I have an extra set of shoes for each rear wheel.
Neat! I also have wondered how they do that.
Thanks all for the good info. @asemaster … In the first instance, do you mean that the caliper piston is pushed out entirely by the emergency brake cable; ie. that if the rear hydraulics fail, it still works?
Those caliper pistons are threaded, if that helps.
@GeorgeSanJose, Yes, the e-brake portion of the caliper is entirely mechanical.
I suppose I should also mention that some late-model Audi/VW use a system like this that is electrically operated and not mechanical. This system requires use of a scan tool to access the braking system to retract the caliper piston during pad replacement.