[aardvarcus]

Well I figured I would write up a post on my project truck. It is a Chevrolet 1991 4x4 2500 Light Duty, aka a 1500 frame and front suspension with a 9.5” Semi Float 14 Bolt rear end. Also known as or equivalent to a GMT400, K1500, K2500LD, light three quarter, heavy half, OBS Silverado, etcetera. I have had the truck for years, and have repeatedly had transmission issues. I had it rebuilt when I first got the truck, and have had to take it back to the shop four times after that to have it repaired. Most recently I have been babying it to keep it from blowing again, and it wasn’t even shifting right with me doing that.

First order of business was swapping my 4L60 Automatic for a NV4500 Manual. I am wanting to do this for reliability, fuel economy, and durability. I chose this transmission because it is heavy duty, the same length, low first gear, and has overdrive. Downsides are that because it is heavy duty it shifts like a truck not a sports car and it is fairly expensive. After scanning craigslist for quite some time, I found a deal and brought my NV4500 home. Then I started to work on this project, which I will chronicle below. Note I am listing items in the order I should have done them, sometimes I got ahead of myself or behind the curve doing one item or another, mainly around when I ran the clutch lines and secured the petal bracket in the front.

Tore the tranny open, didn’t see any chipped gears so I cleaned it as best as I could and reassembled it with new Amsoil fluid. Ordered new clutch, pressure plate, flywheel, prebled hydraulic clutch lines, master, slave, pilot bearing, throwout bearing, etcetera.

Put the truck up on ramps and pulled front and rear driveshafts. Put all my nuts and bolts in sandwich bags, grouping them by components. Pulled transfer case. Supported the engine on jack stands and then the transmission on the transmission jack. Pulled the transmission support crossmember. Then I had to take out all the bell housing bolts, which was the least fun. Then out it came. I bought a harbor freight transmission jack for this project, highly recommend getting some sort of jack designed for this purpose.

Pulled the flex plate. Routed the new prebled clutch lines to the appropriate location. Stripped the interior and dash of the truck, drilled a hole through the firewall where it was stamped to accept the master cylinder. Mounted the clutch petal, and assembled the master cylinder to the firewall using two bolts through the firewall to hold both in place. My truck didn’t have the welded on bracket for the clutch petal mount in the front, so I pulled the wipers and the plastic trim between the hood and windshield. Drilled 3/8” holes through the upper firewall into this drainage space under the windshield. Used nuts and bolts to grab the front of the petal bracket and another set to grab the firewall. Coated the firewall ones with RTV silicon sealer to keep rainwater out of the cab.

All steps from here on out were torqued to specs when available. Installed the flywheel. Tapped in a pilot bearing. Used the centering tool to install a clutch plate and pressure plate. I reused bolts off of a used clutch set that came with my transmission since I had none from the automatic and the set didn’t come with any. Installed the bellhousing cover, throwout bearing, and throwout fork. Installed the slave cylinder and dust cover. Tested the clutch for operation, everything was good so I carried on.

Cut the access hole for the transmission in the floor pan, tracing my metal bracket on the floor and using the stamped part of the floor pan as a reference. I cut a section to the back of this on two sides and bent it up, to give room to slide the transmission straight in. Put the transmission on the transmission jack and lifted it up into place. Had to wiggle, turn, adjust etcetera to get it to slide it. I mounted the transmission as far back as I could to try to hang part of the tail back past the part of the jack that was the pivot for adjusting the angle. That way I could have the wing nuts locking the angle loose and adjust the angle on the fly by pulling down on the back of the transmission with about 50 lbs of force, versus having to push up on the front with 200+ lbs of force, so I had a few degrees of play. I had to put a block of wood under the front to get the right angle on the transmission, and since it is at an angle you have to lift it up as you bring it forward. I had the strap holding the transmission on very tight, so it wouldn’t fall on me. The transmission jack was not the sturdiest thing in the world, which actually helped as you could rotate the transmission around to get the bellhousing bolt holes to line up with the transmission holes to get the bolts to be able to start without having to remove the safety strap on the transmission. Bolted transmission to bellhousing, and removed the jack under the engine.

Reinstalled the transmission frame cross member support and a new rubber support block. Removed the transmission jack, with everything being supported by the truck transmission cross member on the frame and motor mounts. Got my new to me 241C transfer case with the 32 Spline input shaft that came with my transmission on the transmission jack. Used RTV silicone sealant to make a good seal, as the 4wd NV4500 has no rear seal, thus the input seal of the transfer case acts as the rear seal of the transmission. Bolted the transfer case up, a little tricky working the rear driveshaft stub out on the transfer case around the torsion bar cross member, as you had to get the back end up over the cross member first before you could join them together, which is the reason I couldn’t install the transfer case and transmission already bolted together which I would have preferred. There wasn’t enough clearance to actually properly use the jack to install the transfer case, I used it more as a platform and tilted it up into place off of the drivers side drop down for the front driveshaft output. Note that if you had the torsion bars removed and took out that cross member, you could have installed the transmission and transfer case together.

All downhill from here. Reinstalled the drive shafts. Put the selector shaft back on the transmission. Installed the wiring plugs. Note the ones from the automatic didn’t fit the manual (reverse lights) but the ones on the transfer case still hooked up (4wd engagement and speedometer). Checked everything I had done thus far, and started the truck up and test drove it around the yard. Note I tested it in 4wd low, thus if something was an issue (like the clutch releasing) I would be going 1/3 slower than in high range. Worked fine. Pulled back into the shop, tied up some loose ends such as transmission coolant hoses to the radiator, shifter selector, etcetera. Reinstalled the carpet (with a new hole), shifter boot, seat, seatbelts, and the dash. Had to unthread the selector stick from testing to get carpet and boot in and put it back when done. Reinstalled the plastic trim between hood and windshield and installed new windshield wipers and the old wiper arms. Tied up remaining loose odds and ends.

Took it for a real test drive. This was a used transmission, thus it wasn’t perfect. Mostly good, third gear syncro wasn’t working well so you had to RPM match or it would grind. Don’t know if that was user error on the reinstall or just a worn syncro. This is a truck transmission, it doesn’t shift like a car by any stretch of the imagination, loud, clunky, but it “felt” heavy duty. Time will tell whether or not it truly is. Most people would probably want to rebuild a used transmission before install, but based on my inspection of it’s condition and my overall apprehension of the success of this project I just put it in used. I know I will end up taking it back out to have it rebuilt, but hopefully I will get many miles out of it in its present form. I will be monitoring for fuel economy increases as well.

Everyone wants to know cost, so just to ballpark it $700 Transmission with Bellhousing and Tail Housing, Transfer Case, Petal, Used Clutch Assembly, Boot, Shifter, Etcetera. $500 New Flywheel, Clutch, Pressure Plate, Prebled Hydraulic Clutch System. $100 Odds and Ends, fluids, etcetera. Needs another $100 worth of wiring harnesses, switches, Petal Covers, and other odds and ends to be perfect.