As with most things associated with this hobby, it takes much longer to install something than it does to remove it. For transmission installation, this is where you see the biggest benefits of using a lift and transmission jack. It can support the weight for hours and lift the unit slowly into place while you get everything lined up and other items out of your way.
This Tech Tip is From the Full Book, HOW TO REBUILD & MODIFY GM TURBO 400 TRANSMISSIONS. 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. Slowly pour at least 1 quart of clean ATF into the torque converter. Lubricate the bearing surface of the hub and slide the torque converter onto the transmission. At the same time spin the torque converter to help align the input shaft and stator splines. This may require considerable effort. Make sure that the notches in the hub engage with the transmission oil pump.
Step 1: Pour Transmission Fluid
Pour at least one quart of automatic transmission fluid into the torque converter before installing it into the transmission.
If the torque converter is new, and a new bushing was installed in the oil pump, the torque converter is going to be a relatively tight fit, and can be considerably difficult to install. You may have to be patient during this procedure. Several minutes of spinning the converter and pushing it back into the transmission may be required to get it to fully engage. Once fully seated, there is very little room between the back of the converter and the oil pump.
Step 2: Install Converter
The torque converter must be installed and fully seated into the transmission before it can be installed in the vehicle. This may take several minutes, as you need to align the input shaft, stator shaft, and oil pump drive. Turn the converter while pushing it rearward at the same time.
Step 3: Note Space between Converter and Oil Pump
When fully seated in the transmission, there should be very little room between the back of the torque converter and the oil pump.
It may help to place the transmission on the tail shaft and lean it back against a wall when installing the torque converter. This allows the weight of the converter to aid in getting it fully seated onto the input shaft, stator shaft, and oil pump drive.
Step 4: Use Caution
The torque converter can be very difficult to install into a freshly rebuilt transmission. Gravity can be our friend here, and it may be necessary to stand the transmission on end. Here the bellhousing has been strapped to one of the lift posts to install the torque converter.
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 cause oil pump damage.
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 temporarily install one bolt and a piece of flat bar (bent in slightly) to hold the torque converter in the transmission.)
Step 5: Use Strap to Hold Converter (Safety Step)
A retaining strap is used to keep the torque converter from falling out of the transmission until you are ready for the installation. A piece of aluminum flat bar with a 3/8-inch hole in it works well for this purpose.
Determine if the filler tube needs to go in before lifting the transmission in 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 can occur when upgrading the torque converter. If the stock torque converter is being replaced, the new converter should be test fitted to the back of the crankshaft to make sure the hub seats fully. This little detail is often overlooked until the transmission is bolted in place and it’s time to install and tighten the torque converter bolts. Some flexplates do not have the needed bolt pattern for the new converter. Some high-performance converters are also set up for use with larger-diameter bolts than factory converters. It’s better to find out that the flexplate holes need to be opened up before you are ready to push them through and tighten them up!
Step 6: Test Fit Torque Converter (Precision Measurement)
If you are installing a new torque converter, make sure to measure the front hub on the torque converter and recess on the back of the crankshaft. A test fit between the two components is a good idea, before installing the transmission. The converter should fit tightly into the crankshaft, but still fully seat and turn freely. This step is extremely important because the relationship between the converter and crankshaft maintain perfect alignment between the parts.
Step 7: Note Bolt Hole Sizes
Check the size of the holes in the flex plate before installing the transmission. Some aftermarket converters require larger bolts and the flex plate needs to be drilled to accept them. Find this out before installing the transmission and bolting it in place!
Step 8: Use Guide Studs
A couple of guide studs can be fabricated from a 3/8-inch bolt. Cut off the end and slot it to accept a flat-tip screwdriver for easy removal after the transmission is in place.
To help guide the transmission onto the engine, make a couple of guide studs. With a hacksaw, cut the heads off a couple of 3/8-inch bolts and grind the cut end to a point. Slot them with a hacksaw or cutting wheel so they can be turned with a flatblade 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. Then 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. Reach in and spin the torque converter during this procedure 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 immediately! The torque converter may not be fully seated into the oil pump. If the bellhousing bolts are tightened with the torque converter incorrectly engaged and not fully seated, oil pump damage will result.
Step 9: Install Bellhousing Bolts
The upper bellhousing bolts can be difficult to access. A 6-point universal 9/16-inch socket can be used to install them. To help support the socket, wrap it with a piece of electrical tape.
After the bellhousing is 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 two o’clock position) passes through the strap on the transmission oil filler tube.
Step 10: Seat Filler Tube
Make sure the filler tube is fully seated into the transmission and a new O-ring or multiple-lip seal has been installed. The strap on the filler tube is held stationary by the bellhousing bolt.
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 the crossmember in place, and then lowered onto the crossmember.
Step 11: Install Crossmember
After the transmission is bolted to the bellhousing, raise the transmission just far enough to work the crossmember under it and align/install the bolts.
Once lowered onto the crossmember, install and tighten the rear transmission mount bolts. The transmission jack can be removed at this point.
Before continuing with the installation, check the torque converter again to make sure it turns freely, and then install and tighten the torque-converter-to-flexplate bolts. The engine needs to be turned with a large socket on the front of the crankshaft, or with a large flat-tip screwdriver between the bellhousing and flexplate teeth. It is best to install all of the bolts before tightening them to the final torque. This guarantees that the next hole is well aligned to start the bolt as the engine is turned.
Step 12: Install Crossmember Bolts
Install all of the bolts that go through the crossmember to the frame, but do not tighten them. This allows some latitude to align the crossmember-totransmission-mount bolts. Once all of the fasteners are installed, tighten the crossmember bolts first, and then the bolts to the transmission rear mount.
Step 13: Install Torque Converter Bolts
Spin the torque converter to make sure it is not binding. Install the bolts one at a time but do not fully tighten them until all three bolts have been installed. The engine needs to be rotated to accomplish this.
If you find that there isn’t enough clearance, or the torque converter is tight against the flexplate, 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. In any case, 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, when an aftermarket high-performance torque converter is being installed, there is plenty of clearance and some shimming of the converter is required. 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.
Step 14: Use Proper Hardware
Some aftermarket torque converters require custom hardware. Make sure to use grade-8 material here. Soft nuts and bolts work loose and can cause major problems.
Install the transmission cooling lines and tighten them securely. The fittings on the transmission should be held stationary with a second wrench to keep them from moving while the lines are tightened.
Step 15: Tighten Cooling Lines
Make sure to hold the transmission fittings to keep them from turning when tightening the cooling lines.
Install and tighten the speedometer cable and any wires at the plug terminal. The TH400s use an electric downshift solenoid, which 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 driveshaft length. With the driveshaft fully seated, the rear universal joint should have approximately 3/4 inch of distance between the joint ends and the yoke. This ensures sufficient clearance so the slip yoke doesn’t bottom out in the transmission while still providing plenty of engagement with the splines.
Step 16: Check Clearance
With the driveshaft fully seated into the transmission, there should be approximately 3/4-inch clearance between the U-joint ends and the yoke.
Step 17: Add Transmission Fluid
Add 4 quarts of ATF to the transmission and start the engine. Let the engine idle and continue to add fluid until it is on the lower range of the scale on the dipstick. Do not overfill the unit. With the vehicle effectively supported and the emergency brake locked, place the transmission in forward and reverse, then back into park. Re-check the fluid level, and then add as needed. Do not attempt to road test the vehicle until the transmission fluid level is within the full range on the dipstick.
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.
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. Once at the bottom of the range, apply the brakes and place the transmission in drive (D), then neutral (N), then reverse (R), and back to park (P). Check the fluid level again, and add as needed. Leave the level about 1 pint low to allow for expansion of the fluid when the transmission heats up.
Written by Cliff Ruggles and Posted with Permission of CarTechBooks