truck 12 bolt posi question

[kookykrispy]

Hey everyone.

I have a '65 GMC Handi-van with a truck type 12 bolt 3.73 gears in it. My van has 5 lugs.


I came across an ad on the local craigslist where a guy is selling a 12 bolt posi out of a '62 chevy truck. (has 6 lugs). He thinks it has 4.10's but he is going to check and make sure.

Will the posi unit out of the '62 truck bolt into the van's rear end?? Are the splines all the same on truck 12 bolts?

[2tons of fun]

yes.

[Captainfab]

First the truck 12 bolt didn't come out until '63, so a '62 would have the old 10 bolt with the drop out 3rd member. Secondly the '63 & '64 12 bolts had 17 spline axles and coresponding side gears. The 30 spline axles started in '65 and were used thru the end of the 12 bolt in '79. The 5 lug bolt pattern on the 12 bolts started in '71 and went thru '79 in the C10's. Your '65 van has either aftermarket 5 lug conversion axles or has a '71 and newer 12 bolt under it. Hope that helps.

Originally Posted by kookykrispy

Hey everyone.

I have a '65 GMC Handi-van with a truck type 12 bolt 3.73 gears in it. My van has 5 lugs.


I came across an ad on the local craigslist where a guy is selling a 12 bolt posi out of a '62 chevy truck. (has 6 lugs). He thinks it has 4.10's but he is going to check and make sure.

Will the posi unit out of the '62 truck bolt into the van's rear end?? Are the splines all the same on truck 12 bolts?

[Alan's Classic]

Originally Posted by Captainfab

First the truck 12 bolt didn't come out until '63, so a '62 would have the old 10 bolt with the drop out 3rd member. Secondly the '63 & '64 12 bolts had 17 spline axles and coresponding side gears. The 30 spline axles started in '65 and were used thru the end of the 12 bolt in '79. The 5 lug bolt pattern on the 12 bolts started in '71 and went thru '79 in the C10's. Your '65 van has either aftermarket 5 lug conversion axles or has a '71 and newer 12 bolt under it. Hope that helps.

Man, you are just full of cool info. Great job!!

[198plus]

I agree !!!!!!!!!!!!!!!!!!!

Originally Posted by Alan's Classic

Man, you are just full of cool info. Great job!!

[Captainfab]

Thanks guys

I guess after 34 years of working with these trucks, I have acquired a little knowledge on them.

Originally Posted by Alan's Classic

Man, you are just full of cool info. Great job!!

Originally Posted by 198plus

I agree !!!!!!!!!!!!!!!!!!!

[1964C10]

Originally Posted by Alan's Classic

Man, you are just full of cool info. Great job!!

I second that as well!!! Thanks! I just cut and pasted that little tid bit of information for my files lol

[kookykrispy]

Originally Posted by Captainfab

First the truck 12 bolt didn't come out until '63, so a '62 would have the old 10 bolt with the drop out 3rd member. Secondly the '63 & '64 12 bolts had 17 spline axles and coresponding side gears. The 30 spline axles started in '65 and were used thru the end of the 12 bolt in '79. The 5 lug bolt pattern on the 12 bolts started in '71 and went thru '79 in the C10's. Your '65 van has either aftermarket 5 lug conversion axles or has a '71 and newer 12 bolt under it. Hope that helps.

Thanks for the info, but something is not adding up... I think the rules are different for the 12 bolts in the vans.

I can tell you for a fact the 12 bolt under my '65 GMC Handi-van is factory stock 1965 and has 5 lugs, 4&3/4" bolt pattern like the musclecars.

Also, this guy crawled under the truck while I was on the phone with him and told me it is a 12 bolt, and it is a '62.

So.... ???

In any event, if that 12 bolt in the '62 has 17 splines, I don't think it will fit my little van.

Here's a couple pics of my '65 GMC van just for fun:

[lakeroadster]

Man those flat nose vans are awesome. Thanks for posting the pictures.

[Oklahoma]

M 62 half ton came with a 10 bolt, and I switched it for a 67 12 bolt, maybe this guy had the same thing done to it before he got it.

[turp mcspray]

FWIW, I have seen some early truck 12 bolts that had Dana posi units rather than the Eaton unit. I don't know when the switch was made. (The rear I had was a 64) If it is a dana, I don't think any parts are available to rebuild it. At least when I tried, I couldn't find ANY parts for the Dana posi.

[Captainfab]

Ahhhh OK I was thinking of something like a step van. Yeah those vans had the 5 on 4.75 bolt pattern. I just don't remember for sure if they are based on the truck 12 bolt or passenger 12 bolt.....been a long time since I've seen one. I'm thinking it is truck based. The rear end in that '62 can't be the original if it is a 12 bolt, so it's hard to say what year it is. There is a code stamped in the passenger side axle tube that tells what the original application was. You could also pull the cover, and there is a date on the ring gear too. I don't know about those older vans, but the vans from like '71 or '72 and up have wider rear ends than pickups do.

Originally Posted by kookykrispy

Thanks for the info, but something is not adding up... I think the rules are different for the 12 bolts in the vans.

I can tell you for a fact the 12 bolt under my '65 GMC Handi-van is factory stock 1965 and has 5 lugs, 4&3/4" bolt pattern like the musclecars.

Also, this guy crawled under the truck while I was on the phone with him and told me it is a 12 bolt, and it is a '62.

So.... ???

In any event, if that 12 bolt in the '62 has 17 splines, I don't think it will fit my little van.

Here's a couple pics of my '65 GMC van just for fun:

All of the Dana posi units that I've seen were of the 17 spline type ('63/'64). Those are some really stout posi units though.

Originally Posted by turp mcspray

FWIW, I have seen some early truck 12 bolts that had Dana posi units rather than the Eaton unit. I don't know when the switch was made. (The rear I had was a 64) If it is a dana, I don't think any parts are available to rebuild it. At least when I tried, I couldn't find ANY parts for the Dana posi.

[19GMC63]

Cool van... you don't see those things everyday.

[1964C10]

Very cool van! It's in good shape too! I dont envy you having to find parts for it.

[kookykrispy]

Originally Posted by 1964C10

Very cool van! It's in good shape too! I dont envy you having to find parts for it.

Hahaha, yeah parts can be a bit tough to come by, nobody has a resto parts catalog for these things.

Luckily I have a parts van!