There are so many variables that effect the operation of a caliper, it is impossible to place a generic lifespan on them. Because of this, a good mechanic will develop the ability to be able to accurately determine when it is time to replace the calipers. For your example, this article will go over the signs of wear as well as the different options of calipers out there.
Determining Caliper Replacement
Replacing calipers with every brake job would be considered overselling by most customers and regulators. On the other hand, never replacing calipers would be considered underselling by most shops. Typically, there are two groups of customers who should be offered the option of replacing the calipers. To emphasize, notice the word “option”, meaning the customer will have a choice.
Group 1: If the vehicle fits the following criteria the customer should be offered the option of replacing the calipers:
• The vehicle has high mileage
• Original equipment calipers are still installed
• Each set of pads lasts less than the previous set (premature pad wear)
Presenting Caliper Options
When presenting the option of replacing the calipers you should make the following points:
• First, explain to the customer that based on the vehicle’s history and current condition the only way to restore maximum pad life is to service the inside of the caliper. This usually means replacement. As a result, the function of the square cut seal will be restored. (See more info below for a better explanation of the square cut seal).
Group 2: When a vehicle fits the following criteria, the customer should be offered the option of replacing the calipers:
• Start by informing the customer that parts or labor will be required to restore the caliper’s. However, If the caliper requires the replacement of smaller parts, the customer should also be given the option of replacing the caliper (See Figures 34.1). Often times it can actually end up being more expensive to fix the caliper than to replace it.
Note: Without a proper inspection most of the conditions listed above would NOT be found.
More Info: Floating Caliper Operation
Calipers are not “instant on, instant off” parts. This is because they go through a cycle or process during both the “apply” and “release” phases. (See Figure 34.3).
Understanding these 2 processes is key to being able to identify many of the causes of premature pad wear. To begin, the “apply-cycle” starts with the application of the brake pedal, which results in pressure being generated in the hydraulic system. Likewise, hydraulic pressure created in the caliper housing pushes in all directions. In fact, the operation of the caliper works on the principle that things will take the path of least resistance. The easiest thing to move in a floating caliper should be the piston. Hydraulic pressure pushes the caliper piston into the inboard brake pad causing it to press against the inner friction surface of the rotor (See Figure 34.4).
Once the inboard pad is against the rotor, the caliper piston is no longer the easiest thing to move and system, causing pressure increase. Next, the easiest thing to move is the caliper housing. As a result, pressure acts against the caliper housing using the caliper piston as a backstop. This pressure causes the caliper housing to move toward the center of the vehicle on its mounting pins. Inward movement of the caliper housing pulls the outboard pad against the outer friction surface of the rotor (See Figure 34.5). Once both the inboard and outboard brake pads are against the rotor’s friction surfaces, increasing the hydraulic pressure results in even clamping of both brake pads.
A different process takes place to allow the brake pads to release. For example, the part responsible for the release of the brake pads is the square cut seal. The square cut seal is a square o-ring that sits in a machined groove in the caliper housing. You’ll notices that the groove in the caliper housing is beveled towards the open end of the bore. This square cut seal forms a seal between the caliper housing and the piston’s sealing surface (See Figure 34.6).
As the caliper piston moves out to apply, the square cut seal is flexed into the beveled portion of the housing groove. Next, the square cut seal will remain in the stretched position as long as the brake pedal is applied (See Figure 34.7).
Finally, once the brake pedal is released and system pressure goes to zero, the square cut seal returns to its natural relaxed state because of its elastic properties. As the square cut seal returns to its natural state it pulls the caliper piston back with it. The relaxing of the square cut seal is what is responsible for the release of the disc brake pads.
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