Billet aluminum replacement for the 1-2-3-4 clutch apply piston that cracks in GM 6L80 and 6L90 six-speeds, Sonnax 104984-01.
A 6L80 that slips in first through fourth, flares on the 1-2 or 2-3 shift, or burns its 1-2-3-4 clutch pack again shortly after a rebuild may have a cracked apply piston behind those clutches. This is the Sonnax 104984-01 heavy-duty 1-2-3-4 piston, machined from 6061 billet aluminum to replace the cast factory part in the GM 6L80, 6L80E, 6L90 and 6L90E. It belongs in Silverado, Sierra, Tahoe, Yukon, Suburban and Escalade builds, Camaro and Corvette units, CTS-V cars and the Chevrolet SS, especially ones that tow or carry more power than stock.
The 6L80 makes six speeds from five clutches. The 1-2-3-4 clutch, as the name says, is held applied in first, second, third and fourth gear, which puts it to work more than any other pack in the transmission. Its piston sits in the clutch housing; line pressure fed through the pump cover pushes the piston into the frictions and steels to lock the clutch. Because it applies on almost every drive cycle and sees full line pressure under load, the cast OE piston takes repeated stress at the apply face and hub. Sonnax and the rebuild trade report that the cast part cracks in service. Once it does, pressure leaks past the crack, the clutch cannot clamp fully, and the pack slips and overheats.
Low-gear slip is not always the piston. Low line pressure from a worn pump, a sticking regulator valve, or leaking sealing rings in the pump cover feed circuit will starve the same clutch. Check line pressure against commanded pressure first, as laid out in our 6L80 pump failure symptoms guide, and read through the other failure patterns in 6L80 common problems and fixes. With the unit apart, clean the old piston and look hard at the hub and the apply face under good light. A hairline crack is easy to miss on an oily part. If you find one, the clutches alone will not fix the unit.
The listing covers the 6L80, 6L80E, 6L90 and 6L90E from 2006 up. Sonnax describes the 104984-01 as a universal design that replaces both the early and the late factory piston, so you do not need to identify which revision came out of your housing. It is built to drop into the original 1-2-3-4 clutch housing. If you are working on a 6L45 or 6L50, or you are unsure what unit you have, send us the year and VIN before ordering. The rest of our parts for this transmission are on the 6L80 collection page.
| Fitment | GM 6L80 / 6L80E / 6L90 / 6L90E, 2006 and up |
| Part Number | Sonnax 104984-01 |
| Position | 1-2-3-4 clutch apply piston |
| Material | 6061 billet aluminum |
| Coverage | Universal - replaces early and late OE piston versions |
| Shipping Weight | 1.5 lb |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Yes. Sonnax lists the 104984-01 as a universal design that replaces both the early and late OE 1-2-3-4 pistons in the 6L80 and 6L90.
Yes. Use new apply seals from your rebuild or seal kit. The piston is designed to use the factory-style seals in the OE housing.
The cast piston cracks on stock units too, especially high-mileage and towing trucks. If the housing is already open, the billet part removes a known failure point.
It can. Slip in the lower gears may set gear ratio codes such as P0731 to P0734, but a cracked piston often shows up first as flare or harsh shifts before any code sets.
Set clutch clearance, refill with Dexron VI, and clear transmission adapts so the TCM relearns 1-2-3-4 clutch apply.
