As with most things associated with this hobby, installation takes much longer than removal. You’ll see the biggest benefits of using a lift and transmission jack for transmission installation. It can lift the unit slowly and then support the weight for hours while you get everything lined up and move other items out of your way.
This Tech Tip is From the Full Book, GM TURBO 350 TRANSMISSIONS: HOW TO REBUILD AND MODIFY. For a comprehensive guide on this entire subject you can visit this link:
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The first step in this process is to install the torque converter into the transmission. Pour at least 1 quart of clean ATF slowly into the torque converter. Lubricate the bearing surface of the hub and slide the torque converter onto the transmission. Spin the torque converter at the same time to help align the input shaft and stator splines. This may require considerable effort. The final step in the process is to make sure that the notches in the hub engage with the transmission oil pump.
If the torque converter is new, and a new bushing was installed in the oil pump, the torque converter has a relatively tight fit, and it can be considerably difficult to install. You’ll have to have some patience for this procedure; it may take several minutes of spinning the converter and pushing it back into the transmission to get it to fully engage. Once it’s fully seated, there is very little room between the back of the converter and the oil pump.
Once you have installed the torque converter, spin it several times to make sure there are no tight spots or binding. Do not attempt to install the transmission unless the converter is fully seated. Any attempt to pull the transmission up to the engine with the bellhousing bolts can damage the oil pump.
Place the transmission on the jack and secure it with a chain or strap. Use care here to ensure the torque converter doesn’t fall out during this procedure. Adjust the transmission jack so the transmission is angled back slightly while it is raised into position. If you are working by yourself, you may want to install one bolt and a piece of flat bar (bent in slightly) temporarilyto hold the torque converter in the transmission.
Determine if the filler tube needs to go in before lifting the transmission into place, or if there is room to install it afterward. With many modern vehicles, the curve of the bellhousing and proximity to the firewall does not allow the tube to be installed after the transmission is in place and bolted to the engine.
Another big problem I’ve seen is with an upgraded torque converter. If the stock torque converter is being replaced, it should be test-fitted to the back of the crankshaft to make sure the hub fully seats. This little detail is often overlooked until thetransmission is bolted in place and it’s time to install and tighten the torque converter bolts.
Some flex plates do not have the needed bolt pattern for the new converter. Some high-performance converters are also set up for larger bolts than the factory converters. It’s better to find out that the flex plate holes need to be opened up before you are ready to push bolts through and tighten them up!
To help guide the transmission onto the engine, make a couple of guide studs. Cut the heads off of a couple of 3/8-inch bolts with a hacksaw and grind the cut end to a point. Slot them with a hacksaw or cutting wheel so they can be turned with a flat-blade screwdriver. Install them just above the dowel pins on each side of the engine block. As the transmission is raised into position, slide it over the dowel pins. Use the adjusters on the transmission jack to keep the transmission well aligned with the engine. Slide the transmission forward on the alignment studs and onto the dowel pins. Install at least one bolt on each side of the bellhousing. Slowly tighten the bolts evenly and pull the transmission until it is fully seated against the engine. During this procedure, reach in and spin the torque converter to make sure it is not binding in the hub of the engine’s crankshaft. If the torque converter locks up at any point during this procedure, stop! It may not be fully seated into the oil pump. If the bellhousing bolts are tightened with the torque converter correctly engaged and fully seated, oil pump damage will result.
Once pulled up against the engine, with at least one bolt on each side, remove the alignment studs and install and tighten the remaining bellhousing bolts. The upper right-hand bolt at the 2 o’clock position passes through the strap on the transmission oil filler tube.
Raise the transmission high enough to facilitate installing the rear crossmember. Some units lack sufficient clearance to install the crossmember with the rear transmission mount in place. It may have to be installed with the transmission slightly elevated and crossmember in place, and then lowered onto the crossmember.
Once lowered onto the crossmember, install and tighten the transmission’s rear-mount bolts. The transmission jack can be removed at this point. Before continuing with the installation, check the torque converter to make sure it turns freely; install and tighten the torque converter to the flex plate bolts. At this point, turn the engine with a large socket on the front of the crankshaft, or with a large flat-blade screwdriver between the bellhousing and flexplate teeth. It is best to install all of the bolts before tightening them to final torque. This guarantees that the next hole is well aligned to start the bolt as the engine is turned.
If you find that there isn’t enough clearance, or that the torque converter is tight against the flex plate, stop immediately. Either the torque converter hub has insufficient clearance inside the crankshaft, or it is not fully or correctly seated into the inner oil pump gear. Regardless, the torque converter should spin freely when the transmission is bolted to the engine. If it is bound up or tight at this point, the problem must be corrected before continuing with the installation.
In almost all cases, plenty of clearance and some shimming of the converter is required when an aftermarket high-performance torque converter is being installed. Make sure to use Grade-8 fine-thread bolts if new hardware is required to bolt the torque converter in place. The fine threads have greater holding power than coarse threads, and hardened bolts can be torqued to specification so they don’t come loose. Soft bolts do not hold sufficient torque and should never be used to hold a torque converter to the flexplate.
Install the transmission cooling lines and tighten securely. The fittings on the transmission should be held stationary with a second wrench to keep them from moving while the lines are tightened.
Install and tighten the speedometer cable and any wires at the plug terminal. TH350s use a downshift cable that is routed up to the driver’s side of the engine and attached directly to the carburetor or throttle body linkage. The TH400s use an electric downshift solenoid that requires a wire to be attached to the terminal on the passenger’s side of the transmission case.
Install the driveshaft slip yoke into the transmission. Test fit for drive- shaft length. With the driveshaft fully seated, the rear universal joint should have approximately 3/4 inch between the joint ends and the yoke. This ensures sufficient clearance so the slip yoke provides plenty of engagement with the splines but doesn’t bottom out in the transmission.
Install the torque converter dust cover and engine starter if it was removed. Reconnect the battery cables. Make sure that the vehicle is well supported on a lift or jack stands, and that the drive tires are not touching the ground. Lock the parking brake. Make certain that the shifter is in Park, and verify that the parking pawl is engaged before you attempt to start the vehicle.
Add 4 quarts of ATF to the transmission and start the engine. These first few quarts of transmission fluid are picked up and pumped to the torque converter almost immediately. Continue to add transmission fluid with the engine at idle speed until the fluid level registers on the dipstick, but at the bottom of the range or at about one pint low. The transmission fluid expands a little when it heats up, so you do not want to fill it all the way to the full mark when the fluid is cold.
Once the fluid level is at the bottom range on the dipstick, apply the brakes and place the transmission in Drive, then Neutral, Reverse, and back to Park. Check the fluid level once again, and add as needed. Resist the urge to fill the transmission all the way to the full mark. Leave it about 1 pint low until the fluid is completely warmed up.
Drive the vehicle a few miles, gently at first, testing for upshift and downshift points. When it is fully warmed up, check the fluid level and add to the “full” mark. You are now ready to road test the transmission.
Check for automatic upshift points and first gear starts from a standing stop. Verify engine braking in the first- and second-gear selector positions. If you have installed a TransGo shift kit, be aware that you now have control of manual low and that the transmission will not upshift until you move the lever.
Make small adjustments to the transmission upshifts by simply removing the hose on the vacuum modulator and turning the screw inside the fitting. If a TransGo shift kit was installed, see Chapter 6 for further adjustments such as custom tuning the shift points by changing governor springs, removing the spring under the modulator valve, and adjusting the modulator.
Written by Cliff Ruggles and Posted with Permission of CarTechBooks