Automatic Transmission Shift Improvement Kits

What Does a Transmission Shift Kit Do?

A transmission shift kit alters fluid flow through the valve body so your automatic shifts firmer and faster. Factory-calibrated transmissions often build in shift overlap, a brief moment when the transmission is in two gears at once. That overlap smooths the ride, but it also lets clutches and bands slip.

Cutting shift overlap reduces that slippage, which means less heat and less wear on friction parts. For a street-driven muscle car or a truck that tows, that helps your transmission hold up under load. You'll also feel a crisper, more positive shift at every gear change.

Keep your expectations realistic. A shift kit doesn't add engine horsepower, and it isn't a repair for a transmission that already slips. If yours does, read up on driving with a slipping transmission first. If your build needs more than a shift upgrade, browse our full range of automatic transmission parts.

Types of Automatic Transmission Shift Kits

You'll find several types of automatic transmission shift kits here, plus specialty parts for specific drivetrains. Here's what each type covers:

• Valve body shift kits from Trans Go fit late-model units like the 4L60E, 4T65E, 6T40/6T45 Gen-2, 6F35 Gen-2, CD4E, and Toyota U760E.
• Reprogramming kits recalibrate the TH400, C6, 1967-1969 C4, E40D/4R100, and Nissan RE5R05A, and there's a tuneless RFE 7-ball kit.
• B&M Shift Improver Kits and Transpak kits fit GM units including the TH350, TH700R4, 4L60, and 4L60E.
• TCI Trans-Scat valve body kits fit the TH-700R4 and the 1971-1979 AMC Torque Command 727/904.
• Specialty parts include CO2 solenoid shifter kits for Powerglide 2-speeds and CAGS skip-shift eliminators for select Corvette, Challenger, and Camaro 6-speeds.

Each type changes shift feel in its own way. Use the part type, brand, and product line filters to narrow the list to the kits that match your project.

Shift Improver Kit vs. Transpak vs. Valve Body Kit

The right kit depends on how much control you want and which transmission you run. A Shift Improver Kit is the easiest and least expensive option. It firms up shifts with a simple install, which suits most street-driven cars and trucks.

A Transpak builds on that with manual-control options. It suits drivers who want more say over shift behavior, such as racers who shift by hand at the strip. Check the product details to see which manual-control features each Transpak offers.

Valve body shift kits focus on the valve body of specific late-model and import transmissions. Most kits include a separator plate, springs, check balls or valves, and instructions. Contents vary by kit, so check the product details for exactly what's in the box.

If you're freshening a 4L60E while the pan is off, our 4L60E transmission rebuild buying guide walks you through the parts to plan for.

How to Choose a Shift Kit for Your Transmission

Start by confirming exactly which transmission you have, then match the kit to how you drive. Many kits are year- and model-specific, so a 1982-1993 TH700R4 kit won't swap in for a 1993-2006 4L60E kit. Not sure what's under your car? Learn how to identify a 700R4 transmission before you order.

Next, think about how you use the vehicle. Daily drivers and tow rigs usually want firmer shifts without a harsh feel, so a Shift Improver Kit is a common starting point. Bracket racers and drivers who shift by hand often step up to a Transpak.

Then add your vehicle in the fitment tool to guarantee parts fit. Classic Mopar owners will find a Transpak shift improver for 1966-1976 A-727/A-904 transmissions. GM owners running a 1965-later TH400 can choose a dedicated TH400 shift improver kit.

Supporting Parts for a Shift Kit Install

Plan your supporting parts before you start, since a shift kit works best when the rest of the transmission is healthy. Fresh fluid and a well-matched converter help the new calibration perform the way it's designed to.

Most installs mean dropping the pan and getting to the valve body, so it's a natural time to replace fluid. Shop our transmission fluids and additives and use the fluid type your transmission specifies. Follow the kit instructions for any fill or adjustment steps.

If you're also changing your cam, gearing, or stall speed, look at torque converters that match your combination. A converter that suits your engine and rear gear lets the firmer shifts do their job. When your parts list is ready, add your vehicle above and shop transmission shift kits that fit your build.