700r4

[DoubleDingo]

3.08's may be too high if you plan to use the truck as a truck, but 3.42 would be a good gear from what I've heard on here. @HotRodPC Has run a truck with a 454 and 3.42's so he could provide more info from experience

 

[Ricko1966]

3.08's may be too high if you plan to use the truck as a truck, but 3.42 would be a good gear from what I've heard on here. @HotRodPC Has run a truck with a 454 and 3.42's so he could provide more info from experience

He's got granny gear,if he's pulling something heavy. Then don't up shift out of 2 and third as early.

 

[DoubleDingo]

He's got granny gear,if he's pulling something heavy. Then don't up shift out of 2 and third as early.

True. I ran 3.54's behind a stock 350/sm420 with no problem except for steep grades. 70 mph was 2600 rpms. 29 inch tires worked best, but 30 inch weren't bad. For the most part it ran like a raped ape, but long steep grades would slow it down. That 3.54 rear was originally designed to be ran with a 396/th400. A 454 definitely has the ooomph to push the 3.08's, but heavy hauling and/or steep grades may be an issue, and 3.42's would be better in that scenario. Seeing he has a 3500 4x4 dually, going down in tire size is somewhat limited because you'd want to be able to run LT Load Range E rated tires.

Edit: I forgot to mention it got 14 to 17 mpg's if I cruised at 70 or less. But where's the fun in that? The engine liked 3000 rpms for some reason and that was 80 mph. Good old Mean Green, my original '65 C20

 

[HotRodPC]

I don't quite understand how to link one of my posts that talks about the 700R4, to this post it's in one of my only three posts regarding my truck, I had to post about gears and what size differential gears may have came in my 1980 GMC 1 ton, my father ordered it from the factory with a 400 engine and a th400 transmission years later when my older brother inherited it he put the 454 in there with the four-speed manual, it's an older four-speed manual so all you have is granny gear plus three speeds and it seems like the engine's tachometer is pretty high at 55 mph, eats up a lot of fuel when going down the freeway. Somebody made the comment in this post about swapping over to a 700R4, if I could link this post to the one that talks about it which I'm sure there's a way you can do it but I don't know how, but I thought about maybe going to a gear vendor to speed overdrive but that seems like it'll be a little expensive

SO some questions? If it's a dually pick up, it'll be a Dana 70 rear axle and likely all the gear ratios are available. If it's a Single Rear Wheel or Cab and Chassis truck it'll be a 14b full float rear axle. Factory gear ratio options would be 3.21 3.73, 4.10 and 4.56. Notice no 3.42 option. I do beleive they exist now in aftermarket option. And I'm not even sure the 3.21 was an option in the 1 ton, but it was for the 3/4 ton for sure. So this truck you have likely has 4.10's. Most common 1 ton gear ratio of the 70's and 80's. 4.56 was most common in the 60's. Personally, I would NOT put a 700r4 in a 1 ton, and I also WOULD NOT put a 700r4 behind a big block.
The easiest thing to do I believe would be to convert it to NV4500 5 speed manual. Still have Granny gear, but have OD gear also. If you want an automatic, I'd convert to 4L80-E. Yes, you'd have to have a stand alone controller to do it right, but they've come down in price over the years. They're no longer $1000-$1200. I think you can find them in the $400 range now days, and maybe $500 or $600 the better ones with more options at your fingertips by just turning knobs to change shift points and shift firmness.

I'd keep that low rear axle ratio and add the OD. This way you have the better of both worlds. Sitll got the low gear for towing, around town mpg, hill climbs or steep grades, but yet you have the OD to dop the rpms down for better freeway speed cruising. Lower rear end gears also take a lot of strain off of the entire powertrain.