Quick answer
The number on an air brake chamber is stamped on the flat face, the clamp band, or a metal ID tag — often cast right into the housing on highway tractors. Read two things: the type (the diaphragm area in square inches, e.g. Type 30 or a 30/30 for a spring brake) and the stroke (long vs short). Also note whether it's a single service chamber or a spring brake, and the mounting. Those characteristics — not the brand — are what you match to order the correct replacement. If the tag is corroded away, the VIN gets the spec that left the factory.
The number stamped on the old can tells you everything you need to order the right one — if you know where to look and what each part of it means.
Where the number is stamped
Look on the flat face of the chamber, the clamp band, or the metal ID tag riveted to the body. You're after two things: the type number and whether it's a spring brake. On a highway tractor it's usually cast right into the housing, so a wire brush and a rag will find it faster than a parts catalog.
What the type number means
The type is the effective diaphragm area in square inches. A Type 30 has a 30 in² diaphragm; a Type 24 has 24 in². Bigger area means more clamping force at the same air pressure. Drive axles on most road tractors run Type 30; steer axles usually run smaller service-only chambers.
A "30/30" means both halves are Type 30 — a 30 service side and a 30 spring side stacked together. That's the double-diaphragm spring brake you'll find on the drives.
Stroke is the detail that trips people up
- Standard (short) stroke: the older spec, less pushrod travel, matched to a standard slack adjuster.
- Long stroke: more travel before it's out of adjustment — what most modern trucks run so brakes stay legal longer.
- They look nearly identical. Swap one for the other and the brakes go out of adjustment or come up short on travel. Always match the stroke to what came off.
Service chamber or spring brake?
A single service chamber applies the brakes when you hit the pedal — that's the steer axle. A spring brake (the double / piggyback) adds the parking-and-emergency spring and lives on the drives and the trailer. If you can see a second, larger housing bolted behind the first, it's a spring brake, and it gets replaced as a complete unit — never opened.
Lost the tag? Use the VIN
Corrosion eats ID tags. If yours is unreadable, the VIN gets us the spec that left the factory, and the number on the slack adjuster and the axle tag help confirm it. Send us a photo of what's left of the old can and we'll cross it.
Order it right the first time
Match the type, the stroke, and the mounting and the new chamber drops in on the same bolts. PartStop chambers are aftermarket direct replacements cross-referenced to Bendix, Haldex and Meritor, and we confirm fit before it ships — same-day out of Tacoma, 6+ month warranty.
Frequently asked questions
What do the numbers on a brake chamber mean?
The type number is the diaphragm area in square inches — Type 30 = 30 in², Type 24 = 24 in² — and more area means more clamping force. A '30/30' means a Type 30 service side plus a Type 30 spring side (a double-diaphragm spring brake). Stroke (long vs short) is a separate spec you also match.
How do I make sure a part fits my truck?
Use the free VIN lookup at partstop.net/vin (parts verified against your truck's build data), match the OEM / cross-reference number from your old part, or call (253) 600-1351 — fitment is checked before you buy.
In stock at PartStop
Shop these air brake chambers
Premium-quality aftermarket direct replacements — cross-referenced to Bendix, Haldex and Meritor. Same-day shipping from Tacoma, 6+ month warranty.
Fleet pricing
Running a fleet? Buy in packs and save
Chambers are a wear item — stock the shelf and a torn diaphragm is a quick swap, not a parked truck. 2-, 4- and 10-packs drop the per-unit price.
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Need the part, not just the reading?
Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.