Based on my research, air brakes should last between 100k - 200k depending on the driver.
My Berk has 36k on it & when I took it in for service this spring to FL, the mechanic said that at the rate of brake wear on my coach & the miles driven, I should be good for another 25 yrs or so.
I don't plan on having the coach that long but he also said that he'd never had to replace the air brakes on a RV in the 27yrs he's worked for FL.
Check with your mechanic the next time you gt your coach serviced.
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It ain't easy being me...I've tried.
I would think that unless something happens to them like overheating or oil saturation from a leaking wheel seal, they will last many many years. We have 22,000 miles and not the slightest wear noted yet, just checked.
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2015 Legacy 340KP
2012 Wrangler Sport
Variables such as what you tow, mountain driving, driver technique etc are all a factor. But, 100k would be reasonable to expect. Just keep up the maintenance as scheduled.