Originally Posted by Mendocino
Well I had been strongly considering a Marlin Toy Box between the 700r4 and the Toyota LC and was thinking of doing that as a winter project. To adapt the 700R4 to the Toyota TC you need an adapter (mine is from AA) which is the same length as the Toy Box. I was thinking I could remove the AA adapter, install the Toy Box with the 4.7 to 1 reduction and have some serious gears. Years ago I had a Ford F-250 with a six cylinder 4 speed w/granny low (6:1 I think) and 4.56s. The thing was awsome. I really enjoy the ability to use near idle rpm with tons of control.
To add the Toy Box, or put the 40 back together correctly I think I will need to extend the wheel base by moving the rear leafs back. The rear drive shaft has no play in the slip yoke and I think this may have caused some problems on the pinion shim preload (it was crushed according to Squishy). Alas, yet another project
However, UB, you bring up some very good points. The last time I had the thing dyno'd it had 310 ft lbs of torque at 3300 rpm, and 215 HP at 4400 RPM at the rear wheels. [Parenthetically, I was surprised that this 355 HP, 405 ft lb engine lost so much at the rear wheels but was told that was not surprising by the tuner]. I really don't want to eat R&Ps so maybe the 4.56s and Toybox are not such a bad idea. Can I re-gear my 75 LC TC to lower than 2:1? I looked at Mark's gears but they appear to be only for later model year TCs.
There's an old expression my friend Wayne Smith used to say, and I agree with him on this: "The farther you go from stock, the farther you go from that legendary Toyota reliability".
And as an engineer (yes I saw that thread in chat today), I can also say that everything is about trade offs. You already mentioned your rear driveshaft. Even with an SBC moved as far forward as possible, adding extra boxes between the tranny and t-case always makes it shorter, and of course there's always pinion angle to deal with. Lengthening wheelbase is a good way to address that (flipping the spring packs front to back is the usual method, and you can also flip the rear shackle hangers), but at some point with SBC power and low gears you're going to start breaking stuff. With 35s that probably won't start right away, but be warned!
Re: TC, yes Matt is right, the 3 speed gears are 2.3:1 (a 15% improvement), and the gears can be loaded into your 75 case if desired, just requires some shimming on the idler. And you are right, Mark's gears are only for the later split case.
If it were my rig, I'd probably go with the R&P gears, maybe add lockers at that time and be done with it for now. Warning: My view is somewhat slanted in that I don't trailer and I drive mine to and from work every day. For a dedicated trail rig (and large budget) different approaches open up.