How to Clock a Brake Chamber on a Commercial Truck

Clocking a brake chamber is an important maintenance task that ensures proper alignment between the chamber and the pushrod. Misalignment can lead to premature wear, poor braking, and safety issues. This guide will teach you the steps to correctly clock a brake chamber on a commercial straight truck, tractor, or tractor-trailer combo.

Here’s a quick step-by-step guide:

  1. Cage the return spring using the chamber’s caging tool kit to contain energy
  2. Loosen (don’t remove) the two flange nuts attaching chamber to mount
  3. Rotate brake chamber body left or right until pushrod is perpendicular
  4. Confirm 90-degree angle with protractor or angle finder
  5. Tighten flange nuts to torque spec once oriented properly
  6. Release caged spring using the caging tool
  7. Road test vehicle and perform brake checks

What is Clocking a Brake Chamber?

Clocking refers to adjusting the orientation of the brake chamber in relation to the pushrod so that the angle of the pushrod is perpendicular to the air chamber mounting studs. This allows even pressure and wear across the entire brake pad surface area.

Benefits of Proper Brake Chamber Clocking:

  • Prevents uneven brake pad wear
  • Optimizes braking capability
  • Reduces risk of brake failure
  • Prolongs brake system component life

When to Clock a Brake Chamber

You’ll need to clock a brake chamber in these situations:

  • After replacing an old or damaged chamber
  • If uneven brake wear indicates misalignment
  • Following brake job when slack adjuster angle has changed
  • Routine safety inspection reveals improper pushrod angle

Use a protractor to verify the angle – it should be 90 degrees.

Safety First – Caging the Brake Spring

Before beginning, you must cage the brake spring using the caging tool attached to the chamber. This contains the strong return spring so it won’t violently unwind when you loosen the chamber.

Consequences of not caging the spring:

  • Spring tension could crush you against another vehicle
  • Risk serious injury to your body or head
  • Damage to the brake chamber or other components

Follow the caging procedure in your manufacturer’s service manual. Once caged, you can safely loosen the chamber.

Step-by-Step Clocking Instructions

Follow these detailed steps to properly clock your brake chamber:

1. Loosen Clamp Bolts

  • Using a wrench or impact gun, slightly loosen the 2 flange nuts mounting the chamber to the mounting bracket. Do not remove them.

2. Rotate Chamber Body

  • Turn the chamber body left or right until the pushrod is perpendicular to the air chamber studs.

3. Confirm Alignment

  • Place an angle finder or protractor on the pushrod to verify 90 degree angle.

4. Tighten Clamp Bolts

  • With the chamber oriented properly, tighten clamp bolts to the torque spec in your manual.

5. Uncage Spring

  • Use the caging tool to release the spring tension.
  • Remove caging pin and tools.

The brake chamber is now clocked correctly and ready for safe operation. Road test the vehicle and perform several brake applications to ensure proper functioning.

Diagnosing Incorrect Chamber Clocking

Symptoms of poor chamber orientation include:

  • Uneven brake wear on that wheel
  • Reduced stopping power
  • Wheel pulling left or right during braking
  • Excessive pushrod stroke

Use an angle finder on the pushrods of all wheels. If one is significantly different from 90 degrees, the chamber requires clocking.

Uneven pad deposits also indicate misalignment. Inspect the pads during service.


Do I need special tools to cage the spring?

Yes, you need a caging kit designed for your specific brake chamber model. Never loosen clamps without caging the powerful return spring.

How do I access the brake chamber?

Chambers mount to the slack adjuster behind the wheels. You’ll need to crawl under the truck or raise the axle to reach them.

What is the proper pushrod angle?

The angle should always be as close to 90 degrees as possible, i.e. perpendicular to chamber studs.

Can I reuse old clamp bolts?

Reuse undamaged bolts, but replace any worn, corroded or stretched bolts with new SAE grade 8 flange nuts.

Correctly orienting your brake chamber takes precision and attention to safety. But mastering this skill helps optimize stopping distance, prevent uneven pad deposits, and reduce wear on the foundation brake components. With the right tools and these step-by-step instructions, you can accurately clock the chamber every time.

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