Slides over the GM 4L80E 4th clutch piston housing to protect the inner and outer lip seals from rolling or cutting as the drum goes back in.
If you are rebuilding a 4L80E out of a Silverado or Sierra 2500, a Suburban, an Express or Savana van or a Hummer H1, the fourth clutch is one of the few places where a single bad moment on the bench can undo the whole job. This is a three-piece steel installer and protector set for the 4L80E and 4L85E 4th clutch piston, sold as an alternative to tool number T-2926. It guides the inner and outer lip seals into the housing so they go in square instead of folding over, which is the usual cause of a fresh rebuild that comes back with no fourth gear.
The 4L80E is a TH400 gear train with an overdrive section added at the front. In first through third, the overdrive one-way roller clutch inside the overrun drum locks the overdrive planetary so it turns as one unit, and power passes straight through. For fourth, the computer commands the shift and the 4th clutch applies, holding the overdrive sun gear so the carrier drives the ring gear faster than the input; at that point the roller clutch freewheels. The 4th clutch piston sits in its own housing, bolted into the front of the case, and it seals on two lips: one on the inside diameter and one on the outside. Every bit of fourth-gear holding power depends on those two lips trapping apply oil. A lip that is turned back or nicked lets oil bleed off, and the clutch slips every time the truck goes into overdrive.
Sonnax lists no 4th, 4th slip and 3-4 neutral among the recurring complaints on the 4L80-E, and not all of them are seal problems. That is why the diagnosis below matters.
A truck that will not shift into fourth is not always a seal failure. A stuck shift solenoid, a lost speed sensor signal or an AFL valve that starves the solenoids can all hold the transmission in third. Run through our 4L80E shift solenoid diagnosis and the input and output speed sensor guide first. If the electrical side is clean, the transmission is commanded into fourth and it still slips, the 4th clutch circuit is next: piston seals, the housing seal rings, and the frictions themselves. Our 4L80E common problems guide walks through how these failures show up in the shop.
This set is listed for the GM 4L80E, the electronic four-speed used from 1991 through 2009 in Chevrolet and GMC 2500 and 3500 pickups, Suburban 2500, Express and Savana vans and the Hummer H1, and for the heavy-duty 4L85E, which shares the same 4th clutch. It is a bench tool, so the model year of the truck matters less than the housing itself. If you have an aftermarket or modified 4th clutch housing, or you are not sure which unit you have, check the tag on the case or send us the year and VIN before ordering. Everything else for the overdrive section is in the 4L80E parts collection.
| Fits | |
| Application | |
| Reference number | |
| Set | |
| Material | |
| Item weight |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Yes. The listing covers the 4L80E and the heavy-duty 4L85E, which uses the same 4th clutch setup. If your housing is an aftermarket billet piece, measure the piston and bore first.
Plenty of builders have used a feeler gauge or a pick, and plenty have rolled a lip doing it. The sleeve walks the whole circumference in at once, so the lip cannot fold in one spot. On a heavy truck that tows, one rolled seal means pulling the transmission again.
It is one of the first things to check, but rule out the shift solenoids, speed sensors and solenoid feed pressure first. If the unit is commanded into fourth and slips, an air check of the 4th clutch circuit will tell you whether the piston is leaking.
Replace both lip seals, the frictions and steels if they are burnt, and inspect the overrun drum and overdrive roller clutch at the same time, since they live in the same section of the transmission.
It is sold as an alternative to tool number T-2926. We do not claim it is a factory GM part, but it does the same job: guiding the inner and outer piston seals into the housing without damage.
