Replacing Rear Disc Brakes Common Problems
Replacing disc brakes on the front of an automobile is a fairly simple operation. However, when it comes to rear disc brakes the repairs are often more difficult than they first appear. Review common problems associated with replacing rear brake pads and how to overcome them.
What Kind of Rear Brakes
Just a decade ago rear drum brakes were the most common type found on the rear axle of an automobile. Many do-it-yourself driveway mechanics became familiar and comfortable with performing the maintenance service on drum equipped cars and trucks. Today it’s more common to find an automobile with disc brakes on both the front and rear axles. Although the two systems look similar, the operation and the tools needed are quite different on some models.
Type of Rear Disc Brakes
When vehicle manufacturers decided that they wanted to install disc brake assemblies on both the front and rear axles they had a major problem to overcome. This problem is the emergency or parking brake that is typically applied to the rear axle. On the drum brakes, they simply run a cable that operates a lever to push the shoes out against the drum, holding the vehicle firmly in place.
On early rear disc brake systems they employed a complicated rear caliper set up. It used the foot pedal or lever inside the car to operate a cable that attached to an actuator mounted to the caliper. This in turn operated a ratcheting piston inside the assembly. As the lever moved it forced the piston out words producing a clamping force against the rotor assembly. Unfortunately, improved versions of this type of system are still used.
On new automobiles it’s more common to find a parking brake system that uses drum style shoes like they did in the old days. However, the drum is now a hub integrated into the rear rotor. The shoes and the hub are much smaller than a standard rear drum brake assembly. Nevertheless, they operate in the same manner. The manually operated cable attaches to an arm that forces the rear parking shoes outward against the inside of the disc brake rotor hub.
How to Tell what Kind of Rear Disc Brakes You Have
It’s important to know the type of emergency or parking brake system that’s deployed on the vehicle you’re working on. This is because special tools are often needed for a ratcheting piston type system. This is not the case on the more modern drum and shoe E brake system. For these reasons identification becomes critical to a successful do-it-yourself repair.
The easiest way to identify the type of system deployed on your car or truck is to find the rear section of the parking brake cable. If the rear calipers use a ratcheting type piston there will be an actuator lever mounted on the back side of the assembly along with a bracket supporting the cable. This is where they connect the cable. On the shoe and hub style systems, there are no brackets and cables leading to the rear calipers. Instead, the emergency brake cable seems to disappear into the center of the rear axle backing plate.
Problems with Ratcheting Caliper Disc Brakes
Since the caliper piston is manually operated for the parking brake function you can’t use a C clamp to push the piston back into its bore. These types of pistons wind back into the bore making room to install the new pads. The manufacturer installs two dimples into the face of the piston allowing for a spanner wrench or a special rear caliper piston tool to engage without damaging the seals. Trying to force the piston in without the special tool can lead to caliper replacement.
One of the main problems with the ratcheting rear caliper is the heat and dust the components are exposed to normal operation. The other factor leading to problems is that many drivers don’t apply the parking brake to exercise the components. Combining these factors of heat, dust and lack of use makes it common to find a seized ratcheting mechanism. Although these rear calipers can be disassembled and repaired it’s often beyond the realm of a do-it-yourself operation. However, those refusing to surrender can purchase re-manufactured or new loaded rear calipers ready to install.