Allison AT540 AT542 AT543 AT545 Transmission Rebuild Kit

The Allison AT500 series is a four-speed hydraulic automatic built for medium-duty work: school bus chassis, Class A motorhomes, delivery vans, and vocational trucks. This kit covers the AT540, AT542, AT543, and AT545 units from 1971 up, and it is the overhaul set you reach for once the transmission is out and on the bench.

You get the friction clutch plates plus a complete gasket and seal package: the pan and pump gaskets, the front pump and output shaft seals, and the full O-ring and sealing-ring assortment. That is every soft part the rebuild consumes, in one box, so you are not stopping the job to chase individual part numbers. Tear the unit down to the bare case, wash and inspect the steels, and reuse them if they are flat and clean; the frictions, gaskets, and seals all go back in new.

These transmissions come apart for a few repeat reasons: slipping clutches after high-mile bus and RV duty, front pump and output seals that weep onto the driveway, and burnt fluid from years of stop-and-go service. Rebuilding with fresh frictions and a full seal set restores clutch holding capacity and shuts down the leaks instead of patching one symptom at a time.

Fits a wide range of AT540, AT542, AT543, and AT545 applications, including school bus chassis and older Class A motorhomes. Confirm your unit's exact variant before ordering. Ships from the USA, handling in 1-2 business days.