Rebuilding a transmission is one of the hardest repairs to make on any vehicle. They are a complicated mess of plates, small parts, and synchronization. Even some experienced mechanics won’t touch a transmission due to the amount of work involved. As such, if you are going to try rebuilding a transmission on your own, first get the right tools and parts, such as a transmission rebuild kit. Knowing how to choose the right transmission rebuild kit is easy—just get the one that is made for your make and model of vehicle. It should include everything you need; the hard part is the rebuilding.
Remove the Transmission
To remove the transmission on most cars or trucks, you must first remove the transfer case. It is underneath the vehicle. Then, unbolt the motor mounts and the transmission from the crossmember as well as the crossmember from the frame. After doing all that, you’ll need to get an engine lift and attach it to the motor. From here, pull the engine and transmission out as a single unit. When the engine is lifted, all the fluid will drain out of the transmission, so get a bucket ready and use it to catch most of the fluid. Once this is all out of the vehicle, remove the transmission from the engine.
Rebuilding the Transmission
Now that the transmission is out, it’s time to get the rebuild kit ready. Drain the rest of the fluid and then turn the transmission upside down and remove the pan. The valve body needs removing next so repairs can begin. It’s held on by a few bolts on both ends and has the park block rod attached to the manual shift detent by an e-clip. Remove the valve body without removing the park lock from the valve body. Next, take the valve body apart, clean it, and put it back together. You’ll then want to take off the tail shaft assembly from the main housing, clean it thoroughly, and reassemble it. Now you will encounter the larger components, such as the accumulator piston and spring, the front pump, the front band and front clutch, and the input shaft. Once the transmission is taken apart, the majority of parts are replaced which usually includes the disassembled parts you already cleaned, the clutch plates, bands, all seals and rings, and all solenoids.
Next Gen Drivetrain is the only place for premium quality transmission rebuild kits. If you have a Duramax, you’ve definitely come to the right place. We have Allison transmissions for sale—our specialty.