Gear swap

[Powderhound]

My truck has 315 70r 17 4.56 gears and a turbo 400, right now my tranny barely heats up but I have to turn 2900 rpms to do 60 and like 3400 to do 70 I have a bbc 502 and it makes me nervous runnning that high all the time. I was thinking about going to 3.73s that would put me at 2700 rpms at 70. My question is it's a heavy truck and I regularly put 1300 pounds on the bed would that high of a gear heat up my tranny when towing stuff?

[raf2330]

I would consider adding an external trans cooler, I have done that with the TH400's/454 I've had and never had an issue. While I can't say what the 17's do to your ratio, I ran 3.73 for several years with camper on and towing on the 16.5 wheels, it was OK, switched to 4:10 and loved it. Never any tranny issues.

[Da67goatman]

I would suggest an overdrive trans before regearing. A 700r4 just makes more sense, lower first to get moving and benefit of overdrive for the highway.

[jg1977c20]

3:73 is fine most guys who dont like the 4:10's swap to this and say they like it - regarding the tranny swap to an od 700r4 - i'd want that 700r4 freshly built for heavy duty use - they are not as strong as the th400 or th350 especially the sun shell and you never use OD for towing or hauling under any circumstance .

[Da67goatman]

if you use the right parts and be smart about it there's no reason you can't use overdrive when towing.  Upgrade the sunshell with the 6 pinion planetary with corvette servo and oversize .500 tv valve with good quality clutches.  I know a guy running a 468BBC with 44s and 4.56 and he has hauled his boat and his quads without any problems.