What donor axle for my 64?

[GMCMG]

I am two days into my 64 GMC half-ton build project, and have stripped it down to the cab, suspension, and frame. Once the cab is off, I am prepping the frame, and doing suspension/drivetrain. I am converting the front to disc brakes from a 78, and will have 5 lugs. I am looking for suggestions for a donor axle for the rear. I am looking for something that I can preferably bolt on, but am willing to cut/weld spring mounts as necessary. Here are my needs: 2.4 to 2.5 something ratio (was looking at 2.41), would like to match the wheel offsets on the 78 (believe it is a 62" axle, but correct me), don't care about posi or anything like that, will probably stick with drums, and stick with leaf springs. I would like to soften the rear suspension, as this truck will never haul anything, so would be interested in suggestions here, as well. Maybe a car axle/leafs?
Thanks in advance.

[protrash64]

I met a guy who used S10 leafs on his drag truck; GMC/Chevy leaf frame. It sat really low and looked cool, but I dont know how it ran. I remember he said they bolted right in. I have some S10 leafs and could check the length at some point. Cheap at the junkyard, too!!

[Captainfab]

Those are some really tall gears....you must be after either top speed or mpg. The tallest gears I know of in a truck rear are 2.73's, and those were in the mid to late 80's. The truck rear ends from '71-'87 will work for you, but they are 1.5" (~63.5") wider than the one you have now. I think the spring perches will need to be moved also.

[GMCMG]

Originally Posted by Captainfab

Those are some really tall gears....you must be after either top speed or mpg. The tallest gears I know of in a truck rear are 2.73's, and those were in the mid to late 80's. The truck rear ends from '71-'87 will work for you, but they are 1.5" (~63.5") wider than the one you have now. I think the spring perches will need to be moved also.

I'm after MPG. Dropping a 6.2 Diesel out of an 84 in, and a 27% overdrive manual tranny. Hoping to have enough torque to handle gears that tall. That's why I was wondering about a car leaf spring axle, but I haven't been able to find decent information online about dimensions. I know the 79 Trans Ams had a 2.41, but don't know whether or not the dimensions are right.

[GMCMG]

Originally Posted by protrash64

I met a guy who used S10 leafs on his drag truck; GMC/Chevy leaf frame. It sat really low and looked cool, but I dont know how it ran. I remember he said they bolted right in. I have some S10 leafs and could check the length at some point. Cheap at the junkyard, too!!

Thanks; I hadn't given that enough thought. My brother-in-law has a 94 Sonoma, and I looked at the axle (probably too light), and it wasn't wide enough. I never gave a thought to the springs. I've got his bed off in my garage right now (fuel sending unit problems), so when I get home tonight I'll take some measurements.

[62gmc910]

Originally Posted by GMCMG

Thanks; I hadn't given that enough thought. My brother-in-law has a 94 Sonoma, and I looked at the axle (probably too light), and it wasn't wide enough. I never gave a thought to the springs. I've got his bed off in my garage right now (fuel sending unit problems), so when I get home tonight I'll take some measurements.

I don't mean to tell you how to build your truck but the trailing arm suspension is about as good as it gets, the S truck rear axle will handle the 6.2s torque the 4.3 trucks had the same 10 bolt diff as the 1/2 tons that came with the 6.2 and I think your gearing would be a little too tall ' the 6.2 is pretty soggy in the lower rpm ranges unless its turboed. I have seen the 78ish 1/2 ton rears used with 7" ralley wheels widened on the inside that way you keep the same bolt pattern. Some of the caprice/impalas had the truck bolt pattern and I think they are narrower than the trucks

[hill64step]

Originally Posted by 62gmc910

Some of the caprice/impalas had the truck bolt pattern and I think they are narrower than the trucks

What years, and any more details about these? I don't know much when it comes to dealing with rear ends/axles, but I know I want to change for 5 lug and better mpg. I had planned to go with the early 70s 5 lug rear, but I heard it was wider.

[Tx Firefighter]

Yes, the 73-87 rearend is wider, but it's the perfect width for that 78 front suspension you're going to run because it's wider too.

As close as you're going to get is a 2.73 ratio. If you can live with that, the truck 12 bolt is perfect for your application. It's got the right bolt pattern and right width and is quite readily available.

[62gmc910]

Originally Posted by hill64step

What years, and any more details about these? I don't know much when it comes to dealing with rear ends/axles, but I know I want to change for 5 lug and better mpg. I had planned to go with the early 70s 5 lug rear, but I heard it was wider.

Don't know for sure on the year of the Impala rear ends I think they came in cop cars and wagons, but unless you need narrower track the 71 -72 5 bolt coil bolts right in, And as firefighter said the 73-87 12 and 10 bolts track the same as the discs, If you use the truck rear look for one with wider drums

[GMCMG]

Originally Posted by 62gmc910

I don't mean to tell you how to build your truck

That's actually exactly what I'm looking for on here. As much input as possible. I've not ever done a build anything like this before, and there are a lot of things I don't know/haven't figured out. Every suggestion/criticism/comment I can get is appreciated.
You're not the first to tell me the 6.2 will be sluggish at the lower rpms, and I've finally heard enough to talk a little sense into me, so I'm going to go to a 2.73, which I think will keep my rpms around 16-1700 at 65. Does that sound like a more rational range?

Originally Posted by Tx Firefighter

Yes, the 73-87 rearend is wider...for that 78 front suspension you're going to run...a 2.73 ratio. If you can live with that, the truck 12 bolt is perfect for your application...

Yeah, I'm definitely talked into sticking with the 78 and trying to find some 2.73 gears to put in it.

Thanks to EVERYONE who has provided answers!

[62gmc910]

If memory serves correctly I had an 82 chev 1/2 ton 2wd with a 6.2 th700R4 and I think 2.73 gears the truck was light and it worked great,but if you get a 3.08 diff maybe try it out first, the common ratio on 6.2 trucks was 3.42,
a few degrees of extra advance does wonders for those engines