How to Change a Turbo 350 Oil Pumpby Richard Rowe
Never mind what your transmission-phobic friends may have told you; there's no black magic involved in working on an automatic transmission, or any need to pay a transmission shop hundreds of dollars to do a job you can perform yourself. If there's anything particularly quirky about working on an auto like the TH350, TH400, 200R4, 700R4 or 4L60, it's that you don't really need to know how everything works in order to repair it. Transmission repairs like this hinge mainly on the mechanic's ability to work methodically, document everything and follow instructions to the letter.
Remove the transmission from the vehicle and set it up on end so that the torque converter faces up and the tailshaft rests on the ground. You can use a number of cinder blocks arranged in a triangle around the transmission to hold it up. Lift the torque converter off of the transmission input shaft; you'll see the oil pump behind it. Take a picture of the oil pump orientation.
Remove the eight oil pump bolts and examine the bolt holes. You'll note that two of them have threads going all of the way up through the oil pump housing; the rest of the bolt holes are completely smooth. Reinstall two of the oil pump bolts into the threaded holes and screw them in by two to three threads.
Slip the claw-end of your slide hammer behind one of the bolt heads and give it two medium-strength taps upward. Do the same to the other bolt-head. Work back and forth until the pump pops free of the transmission case. You need to be very careful and methodical from this point forward.
Pull the pump free of the housing, moving slowly as though the pump itself were made of nitroglycerin and gunpowder. Peer under the pump with a flashlight as you lift it free, watching for any washers, bushings or seals that remain on the input shaft. Set the pump on the left side of you working surface. Clear the room of other people or animals that might disturb your work.
Pull the seals, washers and components off of the input shaft one at a time. Place them in a line, working from left to right as you remove them. Keeping these components in the order of removal is vital. Use a digital camera to document their exact positions and orientations.
Scrape the old oil pump gasket off of the transmission case, being very careful not to damage or scratch the case with your removal tool. Clean the mounting surface with a wire brush Remove any residual fluid with a rag and some carburetor cleaner.
Install the new oil pump gasket. You'll need a pair of alignment dowels to install the pump. You can purchase a set of specialized, threaded dowel pins for about $15 as of 2010: or you can also make your own by cutting the heads off of a pair of three-inch long bolts of the same diameter and thread pitch as your oil pump bolts. Grind a flat spot on the sides of your dowel pins to aid removal. Either way, install the alignment bolts into two of the pump bolt-holes in the case.
Reinstall the washers and seals that you removed from the transmission in the exact reverse order of removal. Clean each one with your rag and carburetor cleaner and dip them into a container of transmission fluid before sliding them back over the input shaft. Refer to your digital photographs to aid reinstallation.
Pour some transmission fluid over the transmission input shaft to lubricate it. Carefully lower the new pump over the shaft and rotate it so that it matches up with the reference photos you took in Step 1. Slide the pump over the dowel pins and tap the pump downward with a rubber mallet to seat it in the housing. You shouldn't encounter much resistance, so recheck the components you installed on the input shaft if the pump doesn't seat in the housing.
Install six of your pump bolts and torque them to 20 ft-lb, working back and forth across the pump in a "star" pattern. Remove the screw-in dowel pins, and reinstall the two oil pump bolts in their place.
Dunk your new front main seal in transmission fluid. Slide it into the recess in the front of your pump. Tap it into place with your rubber mallet. Once the seal fully seats, give the seal edges a few good taps with a dead-blow hammer to fully seal them to the pump.
Items you will need
- Large, flat working surface
- Sockets and wrenches, full set
- Torque wrench
- Slide hammer
- Rubber mallet
- Flathead screwdrivers
- Needle-nosed pliers
- Gasket scraper
- Carburetor cleaner
- Digital camera
- Oil pump and oil pump gasket/seal kit
- Transmission fluid
- Plastic dead-blow hammer
- "The Haynes General Motors Automatic Transmission Overhaul Manual" Eric Godfrey; 2005
- Car Craft Magazine: TH350 Automatic Transmission - Tranny Tech
- Truckin Web: SW Performance Transmissions Install - Shifty Business