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Old 08-26-2018, 11:28 AM   #1
Warrens69GMC
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Rear axle options, 1964 GMC C2500

I have a friend who has a 1964 GMCc2500 longbed with leaf springs, and he is looking to upgrade the rear axle to a higher gear for better freeway driving.

Current setup per him-
1986 454
Th400
8 lug rear end, 5,13 gearset, leafspring perches
28 inch tall tires rear, 27 inch front tires

So we were thinking 3.55 or 3.73 gears, what can were use as a donar?
Maybe a 1973-1980 Suburban C20 with 3.73?
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Old 08-26-2018, 11:58 AM   #2
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Re: Rear axle options, 1964 GMC C2500

3.73s and 28" tires. Everyone wants to do 75 but no one wants to spend the money on overdrive. My 81 did 3000rpm at 75 350/350 3.08s and 27 in tires
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Old 08-26-2018, 12:26 PM   #3
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Re: Rear axle options, 1964 GMC C2500

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Originally Posted by LVPhotos View Post
3.73s and 28" tires. Everyone wants to do 75 but no one wants to spend the money on overdrive. My 81 did 3000rpm at 75 350/350 3.08s and 27 in tires
I fully understand what you are saying.

Currently the 5.13/28/th400/2500rpms =40.6mph
Thinking the 3.73/28/th400/2500rpms = 55.85mph
Or maybe the 3.55/28/th400/2500rpms=58.69mph

Just trying to get an easy to swap gear from the 5.13 that is in it now. Overdrive may come later.

With a 4l80E-
5.13/28/4l80e/2500rpms-54.15mph

So the axle gearset has to change.
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Last edited by Warrens69GMC; 08-26-2018 at 05:41 PM.
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Old 08-26-2018, 02:07 PM   #4
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Re: Rear axle options, 1964 GMC C2500

I'd convert over to a 14-bolt.
.
http://67-72chevytrucks.com/vboard/s...d.php?t=624445
.
http://67-72chevytrucks.com/vboard/s...d.php?t=550878
.
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Old 08-26-2018, 02:10 PM   #5
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Re: Rear axle options, 1964 GMC C2500

Oops, I'm sorry. I saw you already alluded to that at the end of your post.
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Old 08-26-2018, 11:01 PM   #6
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Re: Rear axle options, 1964 GMC C2500

You could also look at a 34” tall tire 255x85x16 tires on newer chevy 3/4 ton wheels(6.5x16) with the 4 nubs, around 1972. I have the toyo M55 tires in this size and they are 34” tall.

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Old 08-27-2018, 12:20 AM   #7
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Re: Rear axle options, 1964 GMC C2500

With a 454 you could likely get away with a 3.08 gear. But finding a 14 bolt with those gears won't be easy.
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Old 08-27-2018, 12:46 AM   #8
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Re: Rear axle options, 1964 GMC C2500

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With a 454 you could likely get away with a 3.08 gear. But finding a 14 bolt with those gears won't be easy.
What years for the 14 bolt? He wants a bolt in, no major mods to get it in.
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Old 08-27-2018, 02:16 AM   #9
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Re: Rear axle options, 1964 GMC C2500

what axle is in it now? I picked up a leaf sprung D60 out of a 66 gmc with 4.10 and limited slip for $400..

if it has a dana in it, carrier swap and gear choice of that range may be possible and certainly easiest fix..

I believe carriers change between 4.10 / 4.56 so 4.10 carrier or complete axle with one would take taller gears..

good luck!
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Old 08-27-2018, 12:12 PM   #10
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Re: Rear axle options, 1964 GMC C2500

Reaching into my memory so the measurements may not be 100%

Spring center bolt spacing on your gmc 40"

73 up square body C20 43" with a 6" tall frame center section

73 up C30 40" also includes all the 3+3 crew cabs with a 9" tall frame center section

But if you have a Dana 60 in it I would switch the gears and carrier and be done IMO

All those rears you'll find now are at least 40 yrs old and will more than likely need money put in them to make reliable. When I did mine the donor trucks were not very old and the GMC brake drums were scarce(early 80's)
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Old 08-27-2018, 12:54 PM   #11
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Re: Rear axle options, 1964 GMC C2500

^ good point there.. forgot about this thread where I found a bunch of similar info..

http://67-72chevytrucks.com/vboard/s...d.php?t=535453

post 8 in particular expands a little on what Bud posted above..

interested to see what's in there now, good luck!
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Old 08-28-2018, 08:29 PM   #12
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Re: Rear axle options, 1964 GMC C2500

Quote:
Originally Posted by Killer Bee View Post
what axle is in it now? I picked up a leaf sprung D60 out of a 66 gmc with 4.10 and limited slip for $400..

if it has a dana in it, carrier swap and gear choice of that range may be possible and certainly easiest fix..

I believe carriers change between 4.10 / 4.56 so 4.10 carrier or complete axle with one would take taller gears..

good luck!
If it's original it's probably an Eaton HO52
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Old 08-28-2018, 09:50 PM   #13
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Re: Rear axle options, 1964 GMC C2500

I contacted him to get me pictures.
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Old 08-29-2018, 01:55 PM   #14
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Re: Rear axle options, 1964 GMC C2500

If you are looking for a bolt-in swap, you may want to look at a Dana 60 from an 71-72 F250. When I converted my 65 GMC Suburban from 6 lug axles to 8 lug, I used a Dana 60 from an 72 F250 and it fit without modification to the spring perches. These can be had pretty cheap and there are plenty of gear choices available.
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Old 09-01-2018, 06:20 PM   #15
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Re: Rear axle options, 1964 GMC C2500

https://spicerparts.com/calculators/...rpm-calculator
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