73-87 rear axle info needed - The 1947 - Present Chevrolet & GMC Truck Message Board Network

4everGMtrucks · 01-18-2009, 09:43 AM

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 · 01-22-2009, 09:37 PM

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 · 01-23-2009, 12:25 AM

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 · 01-24-2009, 12:21 AM

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 · 01-24-2009, 03:59 PM

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 · 01-24-2009, 05:32 PM

Quote:

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 · 01-24-2009, 05:34 PM

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.

01-18-2009, 09:43 AM	#1
4everGMtrucks Registered User Join Date: Sep 2008 Location: grand junction, co Posts: 18	73-87 rear axle info needed 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?

01-22-2009, 09:37 PM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	Re: 73-87 rear axle info needed 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. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

01-23-2009, 12:25 AM	#3
skchevota Registered User Join Date: Oct 2006 Location: Evans, Colorado Posts: 530	Re: 73-87 rear axle info needed 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.

01-24-2009, 12:21 AM	#4
sierra4x4 Registered User Join Date: Jan 2009 Location: Canada Posts: 308	Re: 73-87 rear axle info needed 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.

01-24-2009, 03:59 PM	#5
4everGMtrucks Registered User Join Date: Sep 2008 Location: grand junction, co Posts: 18	Re: 73-87 rear axle info needed 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? __________________ family motto: THINK! Threre must be a harder way to do it!

01-24-2009, 05:34 PM	#7
sierra4x4 Registered User Join Date: Jan 2009 Location: Canada Posts: 308	Re: 73-87 rear axle info needed 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.



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