4L80E Overhaul Kit 1991

This listing is labeled 1991, but the kit inside is the Transtec number 2224 overhaul kit made by Freudenberg-NOK, and it is catalogued for every 4L80E (RPO MT1) and 4L85E (RPO MN8) from 1991 on. That makes it the right box for the very first 1991 trucks and for everything after: Chevrolet and GMC 2500 and 3500 pickups, Suburban, Tahoe and Yukon XL, Express and Savana vans, the Hummer H1 and the motorhome and commercial chassis that used the same four-speed. If your 4L80E is weeping fluid at the pan rail and servo covers, takes a long breath before it drops into Drive or Reverse, or slips only once it is hot, the soft parts in this kit are what put the pressure back.

What the overhaul kit does in a 4L80E

Every apply circuit in the 4L80E is a sealed hydraulic path. Pump pressure leaves the valve body, crosses gaskets and the spacer plate, rides sealing rings into the spinning drums and finally pushes on a piston sealed by rubber lip seals or molded bonded pistons. If any of those seals bypass, the clutch behind it sees less clamping force than the valve body asked for. The Transtec kit is the sealing side of a rebuild: the case and valve body gaskets, the lip seals, O-rings and sealing rings, and the small rubber parts. It does not include frictions, steels, bushings, bands or a filter, and this version is supplied without the pan gasket, so plan for those separately.

Symptoms that point to tired seals

• Delayed engagement into Drive or Reverse, worst on a cold start
• A flare or soft feel on the 2-3 or 3-4 shift once the fluid is up to temperature
• Slipping under load with no clutch debris in the pan, which suggests pressure loss rather than burnt plates
• Leaks at the pan rail, servo covers, case connector or rear extension
• On early trucks, slip or high-pressure complaints that started after an electrical part was swapped (see the diagnosis notes below)

How to confirm before you tear it down

Slipping on a 1991-1995 truck is not always a seal problem. ATRA Technical Bulletin 266 explains that GM changed the pressure control solenoid for 1994, from the silver Bosch unit to a black Holley design with different oil channeling, and warns that putting a Bosch unit on a Holley-equipped transmission causes high line pressure. The same bulletin notes GM added a new case connector in that update to cut down on leakage, and dropped the output speed sensor and toothed wheel on 4WD units, which can bring on late or missing upshifts if carriers get mixed. Our 4L80E speed sensor symptoms guide covers that side. Once the electrical side checks out, hook up a gauge and compare line pressure in each range to spec, as described in the 4L80E common problems and fixes guide. A range that reads low while the others are normal points straight at the seals in that circuit.

Fitment

The Transtec catalog lists this kit for 4L80E and 4L85E transmissions from 1991 forward, including the Hummer H1 from 1993 to 2005, Express and Savana vans, Suburban, Tahoe, Yukon XL, Silverado and Sierra HD trucks. Because one kit spans early and late units, expect a few pieces to be left over: the 1991-1996 and 1997-later transmissions do not share every seal, and Sonnax shows the valve body itself changed across those years. Lay each old seal next to its replacement before installing. If you want us to double-check, send the year and VIN or the tag number on the case. The rest of the early and late hard parts are on our 4L80E parts page.

Install notes

• Soak lip seals and O-rings in clean ATF, and use assembly gel on the sealing rings so they stay seated while the drums go together.
• Check every bushing while the unit is apart. Worn bushings bleed off the same pressure the new rings are meant to hold; a bushing driver kit makes the swap far easier.
• Inspect the intermediate sprag while it is out. A worn one is a common reason a rebuilt 4L80E slips in second, and a 34-element intermediate sprag is an inexpensive upgrade.
• Air-check each clutch and servo through its feed hole before the valve body goes on.
• Buy a pan gasket and filter, since neither is in this kit. Fill with DEXRON-VI, the fluid GM lists for the 4L80-E in the 2008 Express owner manual, and set the level hot.

Does this 1991 overhaul kit fit later 4L80E transmissions?

Yes. It is the Transtec 2224 kit, catalogued for the 4L80E (MT1) and 4L85E (MN8) from 1991 up, so it covers late trucks and vans as well as the 1991 model year.

Are clutch plates included?

No. This is a gasket, seal and sealing ring kit. Frictions, steels, bushings, bands and the filter are sold separately, and this version does not include the pan gasket.

Why are there extra seals left over after the rebuild?

The kit is built to cover several design changes from 1991 onward, so it includes pieces for both early and late units. Match each new seal to the old one you removed and set the extras aside.

What fluid does a 4L80E take after the rebuild?

GM lists DEXRON-VI for the 4L80-E in its 2008 Express owner manual, and it is the current replacement for earlier DEXRON grades. Check the level hot, in Park, with the engine running.

My 1994 truck has high line pressure after a solenoid change. Will new seals fix it?

Probably not. ATRA notes the 1991-1993 Bosch pressure control solenoid must not be used on a 1994-up Holley-equipped unit or high line pressure results. Fix the solenoid match before you rebuild.

• 4L80E Common Problems and Fixes: The Six Failures That Actually Come Through the Door
• 4L80E Input/Output Speed Sensor Symptoms
• 4L80E Silverado 2500 Common Problems and Fixes
• 4L80E Express Van Common Problems and Fixes