8L45/8L90 Sonnax Shift Zip Kit Valve Body Repair

The Sonnax Zip Kit is the drop-in fix for shift complaints on GM's 8L45 and 8L90 eight-speeds, the transmissions behind 2015-and-up Silverado, Sierra, Colorado, Canyon, Camaro, Corvette, CTS, ATS and Escalade. As these valve bodies age, the aluminum bores that guide the clutch control valves and accumulator pistons wear and start bleeding off control pressure. The result is harsh or bang shifts, flare and slip on the 1-2 or 3-4, delayed engagement, and erratic shift timing that a scan tool will not code for because nothing is electrically broken.

Part number 8L45-8L90-SHIFT-ZIP rebuilds the pressure circuits without reaming. Every Zip Valve is precision-machined to drop straight into the worn bore and reseal the circuit, so there are no special reamers, fixtures or line-boring tools to buy. The kit contains the S1/S5 clutch control valve kit, the S2/S3/S4/TCC clutch control valve kit, and the 1-3-5-6-7 accumulator piston kit with signal accumulator pistons, sleeves, springs, end plugs and O-rings. A detailed technical booklet with inspection and rebuild tips ships in the box.

This is a valve body job. Pull and disassemble the valve body on the bench, clean it, install each Zip Valve and accumulator piston in its location per the printed instructions, then reassemble and reinstall. Done correctly it restores firm, on-time shifts and correct line and clutch apply pressure on a high-mileage 8L45 or 8L90 without a replacement valve body.

Important fitment note: later-design valve bodies updated the S4 valve to a single .531 inch diameter. The clutch control valve in this kit cannot be used in that location, or shift complaints will result. Verify the S4 bore before installing. Ships from the USA; handling in 1-2 business days.