Major issues can arise between air disc brake callipers and water. Trailer air disc brakes are designed to withstand harsh conditions like heat, dust, and water spray. However, if water enters an air disc brake calliper, it will eventually fail. Let’s explore what technicians can do during service to prevent this.

First, it’s crucial to understand the calliper components that protect the piston, adjuster lever, and self-adjusting mechanism.

These components include the piston boot and guide pin boots, brake chamber, adjuster boot, and adjuster plug. They must be in good condition and properly installed to function correctly.

If water gets into the calliper, it will cause ongoing damage to the internal mechanism until the brakes fail.

Piston boot

The self-adjusting mechanism needs to be completely free from contaminants like dust and corrosion to work effectively. This is only possible if the piston boot is undamaged.

If a torn boot is discovered during service, inspect the piston for signs of dust or moisture. If there is any doubt at all, replace the entire calliper to ensure proper operation in service.

Adjuster boot and plug

The brake calliper adjuster is sealed against water and dust in two ways: a boot around the adjuster and an adjuster plug.

The adjuster boot needs to be clean and in good condition. The yellow adjuster plugs are removed for pad replacement and are often not replaced, which leaves the adjuster boot unprotected to deal with dirt and grime on its own.

Mud, dust, and regular movement will wear away the sealing face of the adjuster boot. This is why the adjuster plug must always be reinstalled after service.

Brake chamber

Image: Hendrickson/Supplied

An often overlooked source of water in brake callipers is from the brake chamber. Problems can arise from either an incorrect mounted chamber or from repeated driving through flood waters.

Before installing a brake chamber, ensure the seal and sealing face are in good condition and apply a thin layer of grease on the seal.

Uneven tightening can cause the calliper to cock over and not sit flush, while under or over torquing can cause distortion or movement that will allow for water leaks.

Even a correctly mounted brake chamber can allow water ingress if the vehicle is repeatedly driven through flood waters.

Flood waters contain grit and grime that can accumulate on the piston rod, which will cause accelerated wear of the piston rod seal. It may be best to replace chambers that have been covered in flood waters.

Guide pin caps and boots

Calliper guide pin bushes wear out, guide pin boots can be torn by debris, and guide pin caps can be punctured by stones and rocks.

Inspect guide pin boots and caps for punctures or deterioration. Guide pin bushes should not have more than 2mm of free play. Replacing worn guide bushes minimises calliper movement and uneven pad wear.

By carefully inspecting and repairing these Hendrickson trailer air disc brake components, technicians play a key role in ensuring trailers remain operational and safe despite occasional adverse operating conditions.