4L85E Overhaul Kit, new and ready to install. Fits the 4L85E. Ships fast from the USA.
A 4L85E that weeps fluid from every seam, engages late on a cold morning, or slips once the fluid gets hot after a tow is usually telling you the rubber inside has given up. This overhaul kit is the soft-seal layer for a bench rebuild: the pan and case gaskets, the bonded valve body gaskets, the lip seals, the piston seals, the sealing rings for the shafts and drums, and the O-rings. The product photo shows that full gasket and seal assortment. It is the foundation order for anyone tearing down a 4L85E or the closely related 4L80E from a three-quarter or one-ton Chevrolet or GMC pickup, Suburban, Express or Savana.
The 4L85E is GM's heavy-duty version of the 4L80E (RPO MN8 versus MT1). Underneath it is TH400 gearing with an overdrive section added in front, held by the overrun, forward, direct, intermediate and fourth clutches plus a front band and a rear band. Every one of those clutches is applied by oil that has to stay trapped behind a piston seal and get across rotating sealing rings to reach the drum. Heat from towing and plowing hardens that rubber and wears the ring lands, so apply oil leaks away, the pack clamps weakly, it slips, and the slip makes more heat. A new seal set restores the pressure each circuit was designed to hold. It does not replace worn frictions or steels, which is why most rebuilders order it alongside clutch packs.
Start with a fluid level and condition check, then drop the pan. Clean fluid with an external leak is a reseal job. Dark fluid with lining and metal in the pan means the clutches are already damaged and you need frictions too. If you have the unit apart, air-check each circuit: a clutch that hisses past its piston needs seals, while one that holds air but still slipped in the truck may be fed by a worn valve body. Sonnax documents that checkball sleeve wear in the 3-4 shift valve bore burns the direct clutch on 1995-later units, so a reseal alone will not fix that cause. Our 4L85E valve body testing guide and the 4L85E common problems guide walk through both checks.
This listing is for the 4L85E and shares the 4L80E architecture, and it does not carry a year range. That matters, because GM moved the family to center lube in 1997 and early cases, pumps and sealing rings differ from later ones. Read the ID tag on the right side of the case and match it against the kit, or send us your year and VIN and we will confirm the fit before it ships. If you know your exact year, the dated versions such as the 1997-04 overhaul kit are listed separately, and everything for this unit is on the 4L85E collection page.
| Fits | 4L85E |
| Part type | Overhaul 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.
No. The photo shows the gasket and seal assortment: gaskets, lip seals, piston seals, sealing rings and O-rings. Order a clutch module or a master rebuild kit if your clutches are worn.
The two units share the same architecture, but early (1991-1996) and center-lube (1997 and later) units use different parts in places. Send us your year and VIN or the case tag numbers and we will confirm before shipping.
Only if the clutches are still good and the slip came from lost apply pressure. If the pan has lining material, or the valve body has worn bores, seals alone will not cure it.
Dexron VI ATF, which is the current GM specification for the 4L80E and 4L85E family. Check the level hot in Park.
Reset the transmission adaptive values with a scan tool if your truck's controller supports it, then drive through every shift under light and moderate throttle so it relearns.
