4L80E Master Rebuild Kit 1991, new and ready to install. Fits the 4L80E. Ships fast from the USA.
A 1991 4L80E is a first-year transmission, and after three decades behind a big-block or diesel GM truck, Suburban or van, most of them have either been rebuilt once already or are slipping their way toward it. If yours flares between gears when it is hot, has stopped pulling a trailer the way it used to, or dumps black fluid and clutch material when you drop the pan, this new master rebuild kit is listed for the 1991 model year. The kit shown includes clutch frictions, steel plates, a filter, a cork pan gasket, valve body gaskets, lip seals, O-rings and sealing rings, so the whole soft-parts side of the overhaul arrives in one box.
GM built the 4L80E on the proven TH400 three-speed geartrain and bolted an overdrive section and electronic shift control in front of it. Every forward and reverse range depends on a clutch pack or band holding against line pressure that the pump makes and the sealing rings carry to each drum. Once the frictions glaze and the rings wear, pressure leaks off before it reaches the piston and the clutch slips instead of locking. A master kit replaces all of those wear items at once. It does not replace drums, the pump, bushings, sprags or the planetary carriers, so the hard parts still have to be measured on the bench.
Slipping is not always clutches. The 1991-93 4L80E used a different pressure control solenoid than later units, and a weak or wrong solenoid can make a healthy unit shift soft or flare. Our 4L80E pressure control solenoid guide covers how to test it, and our 4L80E common problems guide walks through the other failures that mimic worn clutches. If the electrical checks pass, line pressure is in spec, and the unit still slips, the packs are done and a rebuild is the fix.
This kit is listed for 1991 4L80E transmissions. The first year has details that later units dropped. Sonnax notes the screw-in temperature sensor in the valve body was used only in 1991; every later year carries the sensor in the internal harness. The 1991 unit also predates the 1997 move to center-gearbox lubrication, which changed several internal hard parts. Clutch and seal parts are largely shared across the early units, but match the ID tag on your case, and if anything looks different, send us your year and VIN before you order. If your truck is a 1992-95 model, the 1991-1995 master kit covers that range, and every early and late option is on our 4L80E parts page.
Mount the case in a J-8763-B holding fixture so you can rotate it during teardown and assembly. Inspect each drum for scoring, cracked tangs and worn splines; a damaged direct or forward drum should be replaced with a 1991-2000 clutch drum rather than reused under new frictions. Measure end play, replace any loose bushings, and set each clutch pack clearance as you stack it. Soak new frictions in ATF before assembly. If you reuse a 1991 valve body, keep the screw-in temperature sensor and do not swap in a later pressure control solenoid. Install a rebuilt or new converter, flush the cooler and lines, and fill with Dexron VI, the fluid now called for in the 4L80E.
| Fits | 4L80E 1991 |
| Part type | Master Rebuild Kit |
| Condition | New |
| Brand | GM |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It is listed for 1991. The clutch and seal parts are similar across the early pre-1997 units, but for a 1992-95 truck the 1991-1995 kit is the listing built for that range. Send us your year and VIN if you want us to check.
It was the first model year. The 1991 valve body used a screw-in temperature sensor that moved into the internal harness for 1992, and the early units used a different pressure control solenoid than 1994 and later trucks.
The kit shown includes a filter and a cork pan gasket along with the frictions, steels, valve body gaskets, seals and sealing rings.
Worn bushings, any scored or cracked drums, a tired sprag or roller clutch, and the torque converter. Many builders add a shift kit at the same time on a towing truck.
Dexron VI, the current GM automatic transmission fluid for the 4L80E. Flush the cooler and lines first so old burnt fluid does not contaminate the new clutches.
