TransGo 4L80E 4L85E Reprogramming Shift Kit, Heavy Duty

The TransGo 4L80E-HD2 is a valve body reprogramming kit for the GM 4L80E and 4L85E automatics, 1991 and up. It rebuilds the way the transmission feeds and holds its clutches so the unit survives high torque and towing loads that cook a stock calibration. Unlike a simple shift-firmness kit, this is the heavy-duty and competition-level package, so it is aimed at trucks, tow rigs, and built engines rather than a mild street daily.

The centerpiece is the dual-feed direct clutch modification. On a stock 4L80E the direct clutch is fed on only one side, which starves it under load and leads to the classic direct-clutch burnup on the 2-3 apply. The HD2 kit routes feed to both sides of the piston so the clutch stays applied and holds real horsepower instead of slipping and glazing. It also raises and controls line pressure through the pump and boost circuit, which prevents the broken case and center support drum that come from either too little pressure or uncontrolled pressure spikes.

Installation is done during a rebuild or valve body service. The kit includes the recalibration springs, valves, and boost components with TransGo instructions that walk through which stock parts to remove and where each new piece goes in the valve body and pump. Made in the USA. This is the part you add when a 4L80E is going behind a Duramax, a big-block, or anything that will put the stock clutch feed and pressure schedule past what it was built for.