4L85E Shift Kit 1991, new and ready to install. Fits the 4L85E. Ships fast from the USA.
If you are rebuilding the valve body on an early GM heavy-duty four-speed, starting with a 1991 truck or van, and the teardown showed a cooked direct clutch or the truck was flaring on the 2-3 shift, this is the kit to put in it. It is a new TransGo shift kit, shown in the photo with its black CORRECTS / PREVENTS / REDUCES box, the springs, valves, bushings and small hardware. The listing is filed under 4L85E, but 1991 is the first model year of the 4L80E, the unit the 4L85E was developed from, so for a 1991 vehicle you are working on a 4L80E. The same hydraulics run through both, which is why one TransGo kit covers the whole family.
The PCM controls line pressure in this transmission by pulsing the EPC (pressure control) solenoid. That signal does not push on the pressure regulator directly; it acts through a boost valve that rides in a bushing in the pump. TransGo calls that boost valve assembly notorious for wear. When it wears one way, boost is too low, the direct clutch comes on soft during the 2-3 shift and burns. When it wears the other way, boost runs away and the extra pressure can crack the case, the direct drum or the piston. The kit replaces the boost valve and bushing with a hardened, wide-land design that cleans itself, adds a relief valve system that caps EPC boost, and changes regulator and accumulator springs. TransGo describes the result as a slight rise in line pressure with short, smooth shifts, not a harsh street-race feel.
Several of those codes also show up from wiring, a bad solenoid or a worn pump, and a kit will not fix those. Start with a line pressure gauge and a solenoid resistance check; our shift solenoid symptoms guide has the test values and explains the difference between an electrical code and a performance code. If the pressure numbers are off, read the valve body problems and testing guide next, because worn bores elsewhere in the body can mimic a tired boost valve.
TransGo lists this kit for 1991 through 2013 GM vehicles with the 4L80E or 4L85E. For this listing, that means 1991 heavy-duty GM trucks and vans built with the 4L80E. GM made running changes during the run, most notably the 1997 move of cooler return oil to the center support, so if your unit has been swapped or rebuilt with mixed parts, check the pump and valve body you actually have. If you are unsure, send us the year and VIN before ordering. You can see every part we carry for this family on the 4L85E parts page, and our 4L80E vs 4L85E comparison explains how to tell the two apart on the bench.
| Fits | 4L85E 1991 |
| Part type | Shift Kit |
| Condition | New |
| Brand | TransGo |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Yes, as long as the truck has the 4L80E. 1991 is the first year of the 4L80E, and the 4L85E that followed shares the same valve body and pressure circuit. TransGo lists the kit for 1991-2013 on both units. Send us your year and VIN if you are not sure what is in the truck.
No. TransGo designed it around a slight line pressure increase with short, smooth shifts. The goal is to stop the direct clutch from slipping on the 2-3 shift, not to bang gears.
Some of the valve body work can be done with the pan and valve body off, but the kit also includes pump and case changes, including the boost valve and bushing in the pump. Most builders install it during a rebuild.
Any burnt clutch packs, the filter and seals, and the pump if its bushing or gears are worn. The kit fixes the hydraulic cause of direct clutch failure but does not restore damaged frictions.
TransGo lists P0731-P0734, P0751, P0756, P0894 and P1870 among the complaints the kit addresses when they come from pressure problems. If the code is from wiring, a failed solenoid or a worn pump, fix that first.
Use the fluid GM specifies for your vehicle. GM's current published spec for the 4L85E is DEXRON VI.
