True Knight
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I just swapped out the TH400 in my M1028 for an electronic overdrive 4L80E. It’s great because I can now drive the truck at 65 on the freeway and the engine is at about 2,000 RPM with the torque converter clutch locked. Here is what it took:
I got the 4L80 from the junkyard. It was in a ‘96 2500 4x4 Suburban with a 454. I highly recommend rebuilding the transmission. You never know what could be wrong with it straight out of the junkyard. Get it rebuilt by a good shop that knows how to make the small improvements to factory setup. The output shaft needed to be shortened about 1/8” to match the 400. This is easily done when the trans is being rebuilt. They also supplied me with a torque converter for the 6.2/4L80 combo. I also had the transfer case rebuilt because it needed a new shift fork and would slip out of 4WD high at some times.
The 4l80 will bolt right up to the 6.2. The dipstick tube from the 4l80 needed just a slight bend to make it bolt up in the same manner as the 400’s tube. The 4L80 has a 32 spline output shaft, and the NP208 transfer case that most of these trucks came with have a 32 spline input, so they will bolt together with no modification.
As for the pedestal mount that bolts between the trans and transfer case, I had to use the one that was factory on the 4L80 out of the suburban. It is about 3.75” shorter than the factory 400 pedestal, but bolts right up to the 4L80 and NP208 and it requires no machining. The 400 mount would need to be machined to fit into the recess on the 4L80 trans. So I took two pieces of 2” square tube and two pieces of 3/8” x 2” steel plate and built a stand to take up the 3.75” between the 4L80 pedestal and the stock transmission mounts on the cross member. I had to notch the top piece of steel plate to clear the bottom transfer case bolt.
Overall, the transmission and transfer case was about 2” longer than stock. This required the cross member to be moved back and new holes drilled in the frame. I was still able to use the all stock 400 shift linkage after I lengthened the rod about 1” with round bar welded into the middle straight section. I also moved the shift linkage support that is bolted to the frame back about 2”. The shift bracket off the 400 was used on the 4L80 and bolted right on. The shift linkage for the transfer case was also lengthened about 1” with round bar welded in the middle. The front driveshaft needed to be lengthened and the rear shaft needed to be shortened.
For the trans cooler lines I ditched the factory setup because the factory lines were smaller diameter and I did not want to run into any cooling issues. So went with all 3/8” rubber trans cooler line, which I connected to the factory 4L80 quick connect fittings from the suburban that cut to about 2“ long, and ran the lines along the top of the passenger frame rail to an aftermarket B&M Super Cooler (PN#70266) in front of the radiator. It’s rated at 20,500 BTUs which will keep the trans plenty cool.
I purchased the trans controller, wiring harness, and remote throttle position sensor from TCI. It is very programmable and I like the way it works. The TCI unit works best with a RPM signal to decide wide open throttle shift points, but can be made to work solely off of the throttle position sensor. I replaced the vacuum pump on the engine with an engine speed sensor from the 6.5 but the sensor signal was not strong enough. So I used the output from the Dakota Digital DSL-2 flywheel tach interface for the tach signal. The flywheel sensor mounted to the torque converter cover. The cover itself had to be modified because it was hitting the starter. I just ground down the cover until it cleared the starter and bolted right up.
For the TPS I made a simple bracket that mounted between the two rear intake manifold bolts (going across from one side of the engine to the other.) Then I mounted one end of the remote TPS to that bracket and routed the cable straight to the throttle linkage on the injector pump. The other side of the cable mounted to the inner fender and connected to the actual TPS.
To finish it off, I got a gear shift indicator out of a late model truck with overdrive. (I don’t remember what year it was.)
So that was about all it took to get it done. It's a fairly big project, but overall not too difficult. I finished the swap in Oct 2010, so its been 3 months with no problems at all. Overall I am very glad I made the swap to the 4L80. And sorry if the pictures are a bit dirty, This was after some extensive 'testing' of the new set up.
I got the 4L80 from the junkyard. It was in a ‘96 2500 4x4 Suburban with a 454. I highly recommend rebuilding the transmission. You never know what could be wrong with it straight out of the junkyard. Get it rebuilt by a good shop that knows how to make the small improvements to factory setup. The output shaft needed to be shortened about 1/8” to match the 400. This is easily done when the trans is being rebuilt. They also supplied me with a torque converter for the 6.2/4L80 combo. I also had the transfer case rebuilt because it needed a new shift fork and would slip out of 4WD high at some times.
The 4l80 will bolt right up to the 6.2. The dipstick tube from the 4l80 needed just a slight bend to make it bolt up in the same manner as the 400’s tube. The 4L80 has a 32 spline output shaft, and the NP208 transfer case that most of these trucks came with have a 32 spline input, so they will bolt together with no modification.
As for the pedestal mount that bolts between the trans and transfer case, I had to use the one that was factory on the 4L80 out of the suburban. It is about 3.75” shorter than the factory 400 pedestal, but bolts right up to the 4L80 and NP208 and it requires no machining. The 400 mount would need to be machined to fit into the recess on the 4L80 trans. So I took two pieces of 2” square tube and two pieces of 3/8” x 2” steel plate and built a stand to take up the 3.75” between the 4L80 pedestal and the stock transmission mounts on the cross member. I had to notch the top piece of steel plate to clear the bottom transfer case bolt.
Overall, the transmission and transfer case was about 2” longer than stock. This required the cross member to be moved back and new holes drilled in the frame. I was still able to use the all stock 400 shift linkage after I lengthened the rod about 1” with round bar welded into the middle straight section. I also moved the shift linkage support that is bolted to the frame back about 2”. The shift bracket off the 400 was used on the 4L80 and bolted right on. The shift linkage for the transfer case was also lengthened about 1” with round bar welded in the middle. The front driveshaft needed to be lengthened and the rear shaft needed to be shortened.
For the trans cooler lines I ditched the factory setup because the factory lines were smaller diameter and I did not want to run into any cooling issues. So went with all 3/8” rubber trans cooler line, which I connected to the factory 4L80 quick connect fittings from the suburban that cut to about 2“ long, and ran the lines along the top of the passenger frame rail to an aftermarket B&M Super Cooler (PN#70266) in front of the radiator. It’s rated at 20,500 BTUs which will keep the trans plenty cool.
I purchased the trans controller, wiring harness, and remote throttle position sensor from TCI. It is very programmable and I like the way it works. The TCI unit works best with a RPM signal to decide wide open throttle shift points, but can be made to work solely off of the throttle position sensor. I replaced the vacuum pump on the engine with an engine speed sensor from the 6.5 but the sensor signal was not strong enough. So I used the output from the Dakota Digital DSL-2 flywheel tach interface for the tach signal. The flywheel sensor mounted to the torque converter cover. The cover itself had to be modified because it was hitting the starter. I just ground down the cover until it cleared the starter and bolted right up.
For the TPS I made a simple bracket that mounted between the two rear intake manifold bolts (going across from one side of the engine to the other.) Then I mounted one end of the remote TPS to that bracket and routed the cable straight to the throttle linkage on the injector pump. The other side of the cable mounted to the inner fender and connected to the actual TPS.
To finish it off, I got a gear shift indicator out of a late model truck with overdrive. (I don’t remember what year it was.)
So that was about all it took to get it done. It's a fairly big project, but overall not too difficult. I finished the swap in Oct 2010, so its been 3 months with no problems at all. Overall I am very glad I made the swap to the 4L80. And sorry if the pictures are a bit dirty, This was after some extensive 'testing' of the new set up.
