Rear Caliper Piston Boot Becomes Brittle on Vehicles Operating in High Temperatures and Extreme Driving Cycles (Install New Silicone Based Piston Boot)

Some customers with Shuttle Bus conversions or other upfits that enclose the rear brake area with tool boxes and other equipment may find that the rear brake caliper piston boots are becoming brittle and over time may crack. This condition is most noticeable on vehicles where the unit is driven in a stop and go drive cycle, followed by a long park or idle time.

During the time that the vehicle is not moving, the heat from the normal "hot soak" of the caliper and rotor is being contained by the body or the aftermarket components around the caliper. The body or the components are blocking air flow to the caliper area and preventing the heat from escaping quickly enough. The heat is causing the piston boot on the caliper to become brittle. Over time the boot can crack.

Important: Remove the rear brake dust shields (1) on C4500 and C5500 Motor Home (U Models) and Commercial Cutaway (V Models) that exhibit this concern. Refer to the graphic above. Once the shields have been removed, proceed with the correction to the caliper.

A new piston boot is available that will tolerate the heat generated in these extreme circumstances. The new part is made from a silicone-based material and is part of the various caliper kits that are now available to service these calipers.

There is a Seal Kit available to rebuild the caliper. There is a repair Kit available that contains seals, a boot and pistons should the pistons need to be replaced. The new caliper assemblies for use with or without In-Wheel Park Brake (RPO J69) also have the new silicone-based boot already installed.

Choose the appropriate kit to address the condition of the caliper and use the related SI rebuild or replacement procedure that applies to the kit chosen.

For vehicles repaired under warranty, use the appropriate published labor operation for the repair made.