Air Brake Chamber Cross-Reference Guide

You pull a brake chamber off a drive axle, wipe it down, and the only marking left is half a part number. Now what? Brake chambers look interchangeable until you put the wrong one on — so before you order anything, it helps to know the four things that actually decide fitment.

Service, spring, or piggyback

A plain service chamber (a Type 20 or 24, say) handles normal braking on a steer or drive axle. A spring brake — the “piggyback” can you see on drive and trailer axles — adds a parking/emergency section behind the service chamber and carries two numbers, like a 30/30. Mixing these up is the most common ordering mistake, so figure out which one you’re holding first.

Reading the size and stroke

The “type” number is just the diaphragm’s effective area in square inches — bigger number, more clamping force. A 30 pushes harder than a 24. Stroke is how far the pushrod travels before the brake’s out of adjustment, and it comes in standard (~2.5″) and long-stroke (~3″). Long-stroke chambers are marked, and you never mix stroke types on the same axle.

Cross-referencing the brands

Once you know the type, the service/spring setup, the stroke, and the port/mount layout, the chamber’s interchangeable no matter whose name is stamped on it. That’s the whole trick — the brand number is shorthand for that spec. GBK chambers cross-reference the common ones, and you can find your number on a brand page: Bendix, Haldex, MGM, or Automann.

Every GBK chamber lists its full “This Part Replaces” table, so you can confirm the match before you buy. Browse brake chambers, or if your number’s worn off, tell us the axle and what came off and we’ll sort it out.

One safety note worth repeating: a spring brake stores a serious amount of force. Never crack one open without caging the spring first.