What transmission is it?? You don't even say if it's automatic or not. Is the '70 a half ton? 12 bolt rear?
The "granny" nickname only applies to first gear, 4th is 1:1. You will need an OD trans to reduce engine speed. (I'm REALLY tired of people seemingly not understanding this concept.)
4,000 RPM @ 60 is BS. You'd need something like a 6:1 rear end to do that with normal tires. What is it ACTUALLY running at?
You could have a low rear end ratio, like 4.11, 4.56, or even 5.13.
3.73's, like a lot of trucks had, give you 70MPH @ 3,000RPM. 3.08 gears would give you 70 @ 2,400.
I don't know about a 4x4 Safari Van and what trans was used, but unless it's a T-5 OD 5 speed, I'd forget it, personally. Late model auto's are a pain, expensive to repair, and IMO just do not belong in a '70 pickup.
Here's what I'd consider doing:
Get a different ring & pinion, leave the 4spd. You'll probably want the low first with a 3.08 or something.
Or, get a T-5 5 speed OD. Cheap, and pretty easy swap from what I've read. Close ratios. Was used in Ford Mustangs, Astro vans, and more.
Or, find a New Process A833 (GM MY6) OD 4 speed out of an 80-85 pickup. Comes with Hurst shifter. Direct drop in to a Sm465 I think, but hard to find. .73 OD, 2,200RPM @ 70MPH with 3.73's.
Also, what engine is in your truck? You say -"going down hill with the wind at my back"- you might make 60. If it's laboring that hard now, chances are it won't like tall gears any better.
Me and my father have been looking at this for a while to get a faster ecomnomical highway cruise out of his '66. we haven't done it yet, but the T-5 seems like the best choice so far, driveability wise. The A833 we just heard about, it's essentially a 3spd with OD, just like the "granny" SM465 is like a three speed with a super-low first. The 3.08's I don't think would be as nice for around-the-town stuff.
Hope this helps some,
Chaz
Last edited by 66Submarine; 06/12/2012 2:05 AM.
