'67 c-20 4x4
 

Picked up a '67 C-20, factory 4-speed & factory 4X4, V-8 couldn't resist.

Its geared so low though, that highway driving is out of the question, I'm guessing the engine's turning 3,000 rpms when going 45 mph. SM-420 with 4th at 1:1.

Mulling over getting a 2.5 - 3.0 axle ratio in it and swap the trans so high gear will be 0.5:1 at the trans, so I can go 70 mph on the highway with engine only turning approx 1500 rpm.

But, I suspect I'd need to swap out some gear in the transfer case too, but I don't know squat about this. I'm thinking it will still be good as a work truck & around the town driving b/c of the creeper gear. Any thoughts muchly appreciated. Thank you.

FWIW, my 93 vette has 6-speed with 0.5:1 6th gear and 3.07 rear end and gets 28 mpg highway. The C-20 only weighs 500 lbs more and I'd expect to get at least 22 mpg on highway with it if it were similarly geared. I know tons about engines but little about gear swaps.

Re: '67 c-20 4x4
 

Checked the tag on the front diff., says 4:55.

Tire dia. is 30.5 so in 4th gear engine is turning 3012 rpm @ 60mph.

3.08's would take it down to 2038 rpm & I'd expect significant fuel savings then.

Re: '67 c-20 4x4
 

you won't have to touch the transfer case. Just make sure to swap out both front and rear ring and pinions. NOTE, your speedometer will probably be off after that.