fj40charles said:
I run a TH400/Atlas 3.8 and 4.88 r/p. That give me a 46:1 crawl ratio (before torque convertor mulitiplication). I think it is about the perfect rate. Get much lower and you'll be driving through the brakes. I get all of the gearing I need with my transfer case so I don't need the lower first gear of a 700r4/4l60. If gearing is an issue, you can get some 2.75 gears for the 400.
TH400 is heavy and long. It is about 3/4" longer than a 700R4/4l60 so it is really not an issue. I've yet to find an obstacle where I did not have enough power with a 350 tbi motor. The loss of power with a TH400 is not a factor for me.
If you want a real efficient auto tranny, then I'd get a PG. Light, short, and very strong.
You people crack me up.
In low-low-low, I am at 400:1 and I do not crawl through my brakes.
I have the option of mulitple transfer case ratios, 1:1; 2:1; 4:1; and 8:1. Each has it's place. Yes, 1:1 is not very useful in a technical section of extreme rocks, but 8:1 stinks in a mud bog too.
There is NO single right answer to these questions, and I have as of yet to see any of the suggestions above be bad, just not right for every rig or situation. A powerglide is a great answer if wheelbase is an concern. A 700r4, Klune, NP205 like mine is a good answer if you have the wheelbase. Everything else inbetween if fine too if it meets the need of that rig.
As for strength of the 350 or 700 - If you are not killing it with poor ratios behind it, it will hold up. I would contend that with good cooling for the tranny, the 6.17 axle gears, the 2:1 NP205, and the 4:1 of the Klune engaged, there is not that much strain on the transmission. If I had just a TH400, Np205, 4.56's and my 44" tires, any tranny would be stressed offroad, unless of course you were into sand dunes and speed...
Again, there is no single right answer. The arguements are fun to watch though.
Ed