Rear Axle swap

[Caddude101]

OK I am doing a frame off on a 66 GMC Short Stepside. I have recently got my frame back from powder coat, Gloss black and man is it pretty. I need to know is there a factory 12 bolt rear axle that will replace the one that is in my 66 now. I would like to keep it 6 lug but I am installing front disc and I do not have my rotors yet so it is really not a big deal if I do go 5 lug. I dont have a welder so I really dont have the ability myself to relocate the saddles on the rear axle but I can swap axles and so forth. I do have a 69 Chevy as a donor but I have not looked at the rear axle to see if it will work.

[fleetsidelarry]

if you mean you have a '69 chevy pickup donor, and it is the same spring style (trailing arm or leaf) as the GMC, then the rear end is a bolt in. It is 3/4" wider each side, however. if you want to go to 5 lug, then the '71-'72 is the ticket, still a direct bolt-in (but, again, slightly wider than yours). if you were willing/able to cut and weld spring/trailing arm perches, then your options would increase. is the GMC leaf spring or trailing arm?

[Caddude101]

I have leaf springs on the rear and the donor is a 69 chevy truck fletside long wheel base truck.

[fleetsidelarry]

Originally Posted by Caddude101

I have leaf springs on the rear and the donor is a 69 chevy truck fletside long wheel base truck.

that's what I was thinking (darn GMCs) the chevy is most likely a trailing arm setup, which will not help you since you have leafs. you will have to look under it, since I think it is possible that it could have optional leafs. if so, you should be good to go.

and I mis-spoke earlier when I said the '69 was wider, it should be the same. the width change came in '70.

if indeed you do have a 12 bolt (if you have a Dana there may be other differences) chevy did go back to leaf springs in '73, so you might want to look for a '73-up 12 bolt.

[Chevy Fleetside]

I dought you have leaf springs in the Chevy but it can happen. If you have leaf springs you can used any rear that uses leaf. I am not 100% sure of this but you can measure to make sure. If so and you want 6 lug just go to your local bone yard and look for a 4x4 rear. They were 6 lug and you might even get a posi out of it.

[kieth]

Originally Posted by Caddude101

OK I am doing a frame off on a 66 GMC Short Stepside. I have recently got my frame back from powder coat, Gloss black and man is it pretty. I need to know is there a factory 12 bolt rear axle that will replace the one that is in my 66 now. I would like to keep it 6 lug but I am installing front disc and I do not have my rotors yet so it is really not a big deal if I do go 5 lug. I dont have a welder so I really dont have the ability myself to relocate the saddles on the rear axle but I can swap axles and so forth. I do have a 69 Chevy as a donor but I have not looked at the rear axle to see if it will work.

I would stay with the 6 lug if you are doing a stock rebuild, If you do want to continue with the 5 lug you can have the axles you currently have modified to 5 lug, they will also have to turn down the axle hub to match the new 5 lug brake drums. It would be less expensive to check into new front disc brake rotors and bearings, you can get them very inexpensively at O'reileys auto parts , I bought new ones the other day without bearings for $32.00 each I am sure you could get the 6 lug ones also......Kieth

Here is a link to a picture of the rear axle hub after it has been drilled for 5 x 5
cost about $100.00 plus the new drums......

http://kieth.smugmug.com/Trucks/66-G...86_ZfxoQ-X2-LB

5 lug brake drum
http://kieth.smugmug.com/Trucks/66-G...30244651_mRnu3

ps we did have to drill out the rear of the backing plate on the 66 because the original adjuster slot was on the front of the drum and the newer 5 lug drum did not have the adjuster slot....on the front side as shown.

[Captainfab]

For a 5 lug rear end a '73-'87 C10, 10 or 12 bolt will bolt up to the springs. The spring pads are slightly off, but there is typically enough movement in the springs to line up with the newer rear end spring pads. If you want to stya with 6 lug wheel bolt pattern, look for one from a '63-'87 K10. Either way, the one issue you will have is the different location of the shock mounts. Your '66 should have them both on the front of the rear end. The '73-'87's have staggered shock mounts.....one in front and one in the rear.