Plugs into the GM 6L80/6L90 input drum so you can air-check the 3-5-Reverse and 1-2-3-4 clutch circuits on the bench before the case goes back together.
If you are rebuilding a 6L80 or 6L90 out of a Silverado, Sierra, Tahoe, Yukon, Escalade, Corvette or Camaro because it lost reverse, slipped in third or fifth, or banged into third, the input drum is the part you have to prove good before the case goes back together. This machined fixture lets you air-check the 3-5-Reverse and 1-2-3-4 clutch circuits on the bench, one port at a time, so a rolled seal or a cracked weld shows up on your workbench instead of on the first test drive.
The 6L80 is a clutch-to-clutch six-speed, and the input housing carries two of its five clutches: the 1-2-3-4 clutch, applied in first through fourth, and the 3-5-Reverse clutch, applied in third, fifth and reverse. Both pistons live in the same welded housing and are fed through sealing rings that ride on the pump cover stator shaft. In the case, those rings seal each feed. Out of the case, nothing does, which is why blowing air into a bare drum tells you very little. This tool takes the place of the stator shaft. The body slides into the hub, its O-rings seal each feed land, and the face is stamped 35R and 1234 so you know which piston you are stroking.
GM's own bulletin on 2006-2009 6L80 and 6L90 vehicles lists exactly those complaints and ties them to a cracked 1-2-3-4 / 3-5-R clutch housing or to leaking pump seal rings.
Do not tear the unit down on codes alone. A sticking 3-5-R regulator valve in the valve body and trapped air in the 3-5-R circuit can mimic a bad drum, and our 6L80/6L90 3-5-R clutch failure guide walks through separating those causes. The broader 6L80 common problems guide covers pressure and solenoid checks. Once the drum is on the bench, GM's test is soap on the weld, a thumb over the air bleed and air into the 3-5-R feed; bubbles mean the housing must be replaced. This fixture makes that test sealed and repeatable and lets you check the 1-2-3-4 circuit separately.
Fits the input clutch drum (1-2-3-4 / 3-5-R housing) on GM 6L80 and 6L90 transmissions used in 2006-and-up GM trucks, SUVs and performance cars. It does not test the 4-5-6 or 2-6 clutches. Early and late 6L80 drums differ internally (GM changed the 1-2-3-4 piston, its housing and the 3-5-R piston for 2008), but the feed hub this tool seals into is the same job on both. If you are unsure what you have, send us the year and VIN. A heavier billet option, the 6L80/6L90 drum leak tester, is also listed, and every part and tool for this unit is in the 6L80 collection.
If the drum fails the test, a replacement 6L80 input drum is the fix, and a master rebuild kit with steels covers the seals and plates for the rest of the job.
| Fits | GM 6L80 / 6L90 input clutch drum |
| Circuits tested | 3-5-Reverse (35R), 1-2-3-4 clutch |
| Construction | CNC-machined aluminum body with O-ring seals |
| Includes | Tester body, bolt, washer, backing plate, 8 O-rings (4 spare) |
| Shipping weight | 2.4 lb |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The 3-5-Reverse (stamped 35R) and the 1-2-3-4 clutch (stamped 1234) in the 6L80/6L90 input drum. The 4-5-6 and 2-6 clutches are tested separately.
It is listed for the 6L80 and 6L90 input drum. GM changed the pistons and piston housing for 2008, so if you are mixing early and late parts, send us the year and VIN and match the housing to your unit.
A slow or soft apply, a piston that will not hold, or a hiss at the hub points to a cut sealing ring or rolled piston seal. Bubbles at the weld or air from the shell means a cracked housing, which GM says must be replaced.
Use regulated shop air in short bursts and follow your service manual's air-check procedure. You are checking that the piston strokes and holds, not loading the clutch pack.
The machined tester body, retaining bolt, washer, backing plate and eight O-rings: four installed on the tool and four spares.
