An automatic slack adjuster connects the brake chamber pushrod to the S-cam and maintains the designed running clearance as the foundation brake wears. Two adjusters can look similar but differ in arm length, spline count, spline diameter, offset, control geometry, and mounting.
Common automatic slack adjuster cross-references
| Common Reference Numbers | GBK Option | GBK Catalog Specification | What to Verify |
|---|---|---|---|
| Meritor R801074 / R803112 Euclid 11402 |
PA801074ASA$36.00 | 6" arm, 28 splines, 1.5" spline diameter | Arm length, spline count, spline diameter, offset, mounting, control geometry, and axle application |
| Bendix 065172 Gunite AS1133 Midland CS56033 Sirco 2172 |
PA1133ASA$36.00 | 6" arm, 10 splines, 1.5" spline diameter | Arm length, 10-spline fit, diameter, handedness, offset, mounting, and control arrangement |
The five specifications that control fitment
- Arm length: measure from the S-cam center to the clevis-pin center using the specified hole
- Spline count: a 10-spline adjuster is not interchangeable with a 28-spline adjuster
- Spline diameter: verify the S-cam shaft diameter, not only the spline count
- Offset and orientation: confirm the arm shape, handedness, and clearance around the axle and chamber
- Mounting and control geometry: confirm the clevis, brackets, control arm, and installation procedure required by the adjuster design
Why the arm length alone is not enough
Both GBK options above use a 6-inch arm and a 1.5-inch spline diameter, but one uses 28 splines and the other uses 10. The correct replacement must match the complete S-cam and mounting configuration.
Do not use manual adjustment to hide a brake problem
Manual adjustment should not be used as a routine way to bring an automatic slack adjuster back into service. Excessive chamber stroke can indicate worn or incorrectly installed foundation-brake components, a seized or damaged S-cam system, an incorrect chamber or clevis setup, a failed adjuster, or another mechanical problem.
When the stroke is outside the applicable limit, inspect the complete brake assembly and correct the cause. Follow the vehicle, axle, and adjuster manufacturer service procedures for installation, setup, lubrication, and inspection.
What to document before ordering
- Complete part number stamped on the original adjuster
- Arm length and the clevis hole being used
- Spline count and spline diameter
- Offset, handedness, and arm shape
- Control arm or bracket arrangement
- Axle position and brake chamber size
- Photos showing both sides of the installed adjuster
Browse GBK automatic slack adjusters, or search the Bendix and Meritor cross-reference pages.
Send GBK the original number and installation photos when the spline, arm, or control arrangement cannot be confirmed.
Cross-reference numbers identify possible replacement options. Buyers and installers must verify the arm length, spline count, spline diameter, offset, mounting, control geometry, brake system, and axle application before installation.
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