73-87 rear axle info needed

[4everGMtrucks]

i'm trying to find out if there are differences in the amount of axle splines on a73-87 1/2 ton 2wd vs 4wd????, are the housings the same?? and where will i find the i.d. numbers on the housing's to decipher the gear ratio. i've got a 4wd complete axle w/3:73's (supossedly) and am wondering if my 5 lug 2wd axles might just slip right in?

[Mike C]

There are at least (2) different axles, the 12 bolt which has 30 spline axles and the 10 bolt that has 28. I know their are other differences as well such as brake drum width. This would effect the housing length as well.

You just need to find like and like to swap.

[skchevota]

As stated if it is a 10 bolt, the axles will be 28 spline up till 88 then they went to 30 spline in the 4x4. The width might be differant though. I know the 88-98 have diferant widths for the 9.5" 14 bolt between the 2wd and 4x4, and they both have 6 lugs.
As for the ratio, if it dosnt have a ratio tag on it, the pull the cover and count the teeth.

[sierra4x4]

If it is a 12 bolt 73-81 than yes you can swap the 6 lug shafts for the 5 lug shafts but, the shock mounts are slightly different. I have swapped a 5 lug diff into a 4wd and swapped to 6 lug shafts then cut and re-welded the shock mounts. You could just use different shocks instead of cutting and re-welding th mounts.

[4everGMtrucks]

thanks for the info, but where would the ratio tag be. and if i can't find it and end up pulling the cover and count the teeth on the ring gear do i also have to count the teeth on the pinion gear? and how do i do the math to figure out the ratio?

[LONGHAIR]

Originally Posted by 4everGMtrucks

if i can't find it and end up pulling the cover and count the teeth on the ring gear do i also have to count the teeth on the pinion gear? and how do i do the math to figure out the ratio?

It is simple division
41 divided by 10 = 4.10
41 divided by 11 = 3.73
41 divided by 12 = 3.42
40 divided by 13 = 3.08

etc.

[sierra4x4]

If your diff is a 10 or 12 bolt their will not be a tag. Their will be an axle code stamped on the pass side axle tube facing forward a couple of inches away from the center section. If you do pull the cover off the ring gear (big one) will have the #of teeth stamped into it eg. 41:11 which is 3.73. it will also have the date and part # all in the same spot.