6L80 Heavy Duty Billet 1-2-3-4 Clutch Apply Piston

The 1-2-3-4 clutch in a GM 6L80 is applied in first through fourth gear, so its apply piston sees more cycles and more line pressure than anything else in the unit. The factory piston is cast aluminum, and on high-mileage or tuned trucks it cracks around the apply face and hub. Once it splits, the clutch loses apply pressure and the symptoms show up as slipping in the lower gears, a flare going into second or third, or a burnt 1-2-3-4 pack that comes back a few thousand miles after a rebuild. Replacing the clutches without replacing a cracked piston is how a unit ends up on the bench twice.

This is the Sonnax 104984-01 heavy-duty piston, machined from 6061 billet aluminum instead of cast. The billet material and the reinforced apply area handle the pressure spikes that break the OE part, and the design is universal - it covers both the early and the late factory piston versions, so you do not have to identify which revision came out of the drum before you order. It drops into the OE 1-2-3-4 clutch housing and uses the factory seals and retaining ring.

Fits the 6L80, 6L80E, 6L90, and 6L90E six-speed automatics from 2006 up - the units behind the LS and LT V8s in Silverado, Sierra, Tahoe, Yukon, Suburban, Escalade, Camaro, Corvette, CTS-V, and the Chevrolet SS. On the bench, pull the 1-2-3-4 housing, inspect the old piston for cracks at the hub before you assume the clutches were the only failure, install the billet piston with fresh apply seals, then set 1-2-3-4 clutch clearance to the GM spec with selective plates before the drum goes back in the case.