I'm kinda with you Max.
No, I picked up a standard replacement shaft, replaced the drum while I was at it and replaced all the frictions and steels while I had it open. This version has 35k miles since it was last opened up. The input shaft failure caused the overrun frictions to weld themselves to the steels. I had no reverse when I limped it home. Luckily a) I was only 2 miles from home when it happened and b) I didn't pull forward into any spot I wouldn't have been able to back out of.
When it comes to the H3, the 4BT and the 4L60e, it is somewhat a marriage of necessity, not of choice. I did quite a bit of research and each alternative has several drawbacks. Obviously the existing 4L60e has its inherent weaknesses behind a torque monster diesel. But it fits, the adapter is available, and the rest of the driveline remains stock. BIG plus. I looked seriously at just going to a 4L80e. The 80 is longer than the 60 which will be an interference with the fixed crossmember to the rear of the transfer case. The transmission crossmember would have to be fabbed, which is not a huge obstacle. The next major point would be to adapt a transfer case. Of course the H3 uses the most oddball transfer case on the planet. Electric shift, oddball 5 bolt interface, no standard or aftermarket availability of an input shaft in 32 spline to fit the 80, passenger drop - one of the few that drop on that side. In addition, even if you could get an adapter custom made, your are likely into the rear crossmember. Add driveshaft work and it all starts to add up into a major undertaking with several custom parts. Add to that now you either need to add cable shifters for your new (different) transfer case or find the electronic interface and integrate that somehow.
Now that adventr has some hard parts worked out for the 6L80e that may be a viable option. There are still some big obstacles. First, you would need to run a standalone box to interface to the onboard TCM in the trans. I think the aftermarket has that worked out. You will still need a HP tuners license and hardware to connect to the TCM to reset the shift points etc to fit the diesel so add that to the cost. Second, the front end interface will need some new hardware. The offset of the cummins to GM adapter mimic a genI/genII/LTx block. The dimensions for the LSx flywheel to bellhousing face are different. To get it to bolt up would require probably a new flexplate with the right offset and bolt circle. That would likely be another custom piece in addition to the output shaft and transfer case adapter.
So I agree with your impact wrench analogy, when the converter is locked. When unlocked the converter should take up a lot of that effect. When I regeared, I went with 4.10s instead of 3.73 for a few specific reasons. One of those was to keep the engine at the higher end of the efficiency band rather than lower in it. The thought process is the higher engine speed should keep some pump flow up and hopefully increase longevity. Right now I cruise at 70 at 2000 rpm on 35s. Ideally the 4BT would prefer to be about 200 RPM lower for max efficiency which 3.73s would have gotten me. Right now I lockup the converter in 4th at 55 mph which puts me around 1700 RPM. Once locked it will stay locked until under 50 MPH which is right at 1500 RPM. I think I am going to raise those limits to not be locked at such a low RPM where the engine has the ability to deliver almost full torque and beat on the input like that. This US shift controller is quite flexible in the gear shifting and line pressure, but doesn't have much option on the lockup controls. The lockup is at a fixed speed regardless of throttle position. Setting a lower TPS position for lockup works only to a certain point. When I am on the highway cruising at 70+, i want to be able to roll in the throttle on hills and overpasses to maintain speed without kicking out. However to do that I have the disengage/ do not engage set at 85% TPS. This means when I am merging on the freeway at 75% throttle, I will lockup when I get to 55 regardless.
I think US Shift has some updates out and I may look into them in the future to give some flexibility. I think staying away from the ability to go full torque, locked converter at low RPM will at least keep me out of a potential danger zone for now. Need to tweak my settings a bit more with the new knowledge.
