From October 2001 issue.

Why do you need long-stroke chambers if you have automatic slack adjusters?

“Well, just remember that the drum will expand from heat build-up, so even though an ASA starts out keeping a cool brake at 1-1/2 inches of stroke, if that drum expands very rapidly due to severe use going down a grade, the automatic adjustment’s not going to be able to keep-up with that,” warns Ohio brake expert Dick Radlinski. “Also, ASAs don’t always do a perfect job of keeping brakes in adjustment. There’s evidence that more stroke range will let auto adjusters work more efficiently.”

Radlinski points to A U.S National Transportation Safety Board survey: of 12,224 Type 30 brakes inspected, 9541 were manually adjusted units. About 26% were at or beyond two inches, and 13% of the overall sample were at or beyond 2-1/4 inches.

Even with ASA-equipped brakes (2683 units tested), there still were 15% with stroke at or beyond two inches, and 4% overall at 2-1/4 inches or worse.

“ASAs work pretty well when you’re way out of adjustment-2-1/4 inches or more,” he notes.”But they’re still not perfect at keeping the stroke fully within the two-inch legal limit.”