A distributor adding brake chamber diaphragms to a range faces the same question every time: which sizes first. Holding all of them in depth ties up money in sizes that may sit on the shelf for a year. Holding too few means telling a workshop to come back next week, and workshops do not come back.
There is no universal answer, but there is a better starting point than guesswork.
What a cross-reference count tells you
Every size we supply is mapped to the part numbers other companies use for the same diaphragm: vehicle manufacturers, brake system makers and aftermarket brands. The more catalogues list a size, the more vehicle builds and chambers it is likely to fit.
Across our range of 21 sizes the spread is uneven. The three broadest:
| Size | OEM numbers | Brands |
|---|---|---|
| Type 24 long stroke | 63 | 33 |
| Type 24 normal stroke | 51 | 21 |
| Type 30 normal stroke | 45 | 22 |
Type 24 long stroke is listed under more numbers than any other size we supply. At the other end, four sizes in our range have no verified OEM number yet; we still supply them, by Type and stroke.
A size with many numbers is not automatically a size that sells. It is a size that many catalogues describe — which usually means many vehicle builds, several brake system makers and a long service history. When you have nothing better, that is a reasonable first proxy for demand.
What it cannot tell you
A cross-reference count is a global figure. Your market is not global.
- Fleet mix differs by region. The truck makers and brake system suppliers that dominate one market may be minor in another, and the chamber sizes they prefer differ with them.
- Vehicle type matters. A distributor serving trailer builders and one serving bus operators will see different sizes moving.
- A count is not a sales figure. We do not publish sales data, and a number of catalogue listings is not one.
So treat the table as a starting assortment, then let your own records correct it within the first few orders. The chamber numbers your workshop customers ask for are better data than ours.
Stock both strokes, or neither
If you carry a Type, think twice before carrying only one stroke. Normal and long stroke diaphragms are not interchangeable in either direction: a workshop with a long stroke chamber cannot use the normal stroke part on your shelf, and fitting it anyway removes the brake's travel reserve. A Type stocked in one stroke serves only the chambers built for that stroke, and the rest walk out.
Our guide to normal and long stroke explains the difference.
A sensible first order
- Start with the sizes that have the broadest coverage, in both strokes where both exist.
- Add the sizes your own customers have already asked for, by chamber number.
- Order thin across many sizes rather than deep in a few, then reorder on what moves.
- Before committing, fit samples. We send up to ten pieces free of charge, across whichever sizes you choose; you cover the shipping.
The whole range, with every OEM number we cross-reference, is in the size chart. Distributors get tiered pricing — the distributor page says what we ask and what you get.