De-Code Rear Axle - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Ironhorse** · 01-30-2008, 09:05 AM

Trying to de-code the rear axle on what I "think" is an '80 GMC 3/4 ton 4x4 LB. Frame with running gear, 4 speed trans., transfer case and what I know is not the original cab. Has the large hubs on rear axle with the following:

K JU G 3 081 stamped into the upper right hand rear axle tube. Fourteen bolts on the rear housing.

Not really familiar with the "square body" trucks and my "red book" only covers '46-'72 years. Anyone help with a de-code? No sheet metal from cab vin to help pin down the year. Tried doing a search but only came up with RPO codes but no stamping codes.

James McClure · 01-30-2008, 09:35 PM

Iron: Try your local Chevy or GMC store. Parts should be able to decode it for you with reasonable accuracy. You can pull the ratio yourself without to much trouble if you have a mind to. I just explained this to someone but forgot where so I'll run through it again. Pop the pumpkin cover and rotate the ring gear till you see a series of numbers. Look for a series that looks like this " 15:41 ". It is important that the numbers be seperated by a ":". Now that you have that info, devide 41 by 15 (please note your numbers will be different) and you get "2:73" thats the ratio. Between knowing that and knowing your brake size you can pretty much get any part you want without knowing the exact year. You have the heavy rear axel so brake size will be either 13 X 2.5" or 13 X 3". jim

**Ironhorse** · 02-01-2008, 11:15 AM

James, Thanks for the reply. Seeing as how the truck in question is not mine not sure about pulling the rear cover to check the gearing. Will call my "GM connection" at the local Chevy house and give him the info, see what he comes up with.

**Ironhorse** · 02-02-2008, 07:09 PM

My GM connection came thru for me. Looks like it is a ' 79 GMC, not an ' 80 as I thought. The axle code says it has 4:10 rear gearing with the big brake shoes. Truck actually belongs to my brother-in-law, wants to sell it as a project truck seeing as how he just recently purchased a ' 83 1ton 454 4 speed 4x4 dually. In his words, " Bigger is Better".

01-30-2008, 09:05 AM	#1
Ironhorse Senior Member Join Date: Jul 2001 Location: Wellington, Ks Posts: 10,347	De-Code Rear Axle Trying to de-code the rear axle on what I "think" is an '80 GMC 3/4 ton 4x4 LB. Frame with running gear, 4 speed trans., transfer case and what I know is not the original cab. Has the large hubs on rear axle with the following: K JU G 3 081 stamped into the upper right hand rear axle tube. Fourteen bolts on the rear housing. Not really familiar with the "square body" trucks and my "red book" only covers '46-'72 years. Anyone help with a de-code? No sheet metal from cab vin to help pin down the year. Tried doing a search but only came up with RPO codes but no stamping codes. __________________ 1971 Chevy 1/2T 4x4 LWB 350 V-8 Was sm465-now 350TH/np205 Tilt, Tach, Towhooks Original Truck AM/FM Wellington, Ks Last edited by Ironhorse; 01-30-2008 at 09:09 AM.

01-30-2008, 09:35 PM	#2
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: De-Code Rear Axle Iron: Try your local Chevy or GMC store. Parts should be able to decode it for you with reasonable accuracy. You can pull the ratio yourself without to much trouble if you have a mind to. I just explained this to someone but forgot where so I'll run through it again. Pop the pumpkin cover and rotate the ring gear till you see a series of numbers. Look for a series that looks like this " 15:41 ". It is important that the numbers be seperated by a ":". Now that you have that info, devide 41 by 15 (please note your numbers will be different) and you get "2:73" thats the ratio. Between knowing that and knowing your brake size you can pretty much get any part you want without knowing the exact year. You have the heavy rear axel so brake size will be either 13 X 2.5" or 13 X 3". jim __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

02-01-2008, 11:15 AM	#3
Ironhorse Senior Member Join Date: Jul 2001 Location: Wellington, Ks Posts: 10,347	Re: De-Code Rear Axle James, Thanks for the reply. Seeing as how the truck in question is not mine not sure about pulling the rear cover to check the gearing. Will call my "GM connection" at the local Chevy house and give him the info, see what he comes up with. __________________ 1971 Chevy 1/2T 4x4 LWB 350 V-8 Was sm465-now 350TH/np205 Tilt, Tach, Towhooks Original Truck AM/FM Wellington, Ks

02-02-2008, 07:09 PM	#4
Ironhorse Senior Member Join Date: Jul 2001 Location: Wellington, Ks Posts: 10,347	Re: De-Code Rear Axle My GM connection came thru for me. Looks like it is a ' 79 GMC, not an ' 80 as I thought. The axle code says it has 4:10 rear gearing with the big brake shoes. Truck actually belongs to my brother-in-law, wants to sell it as a project truck seeing as how he just recently purchased a ' 83 1ton 454 4 speed 4x4 dually. In his words, " Bigger is Better". __________________ 1971 Chevy 1/2T 4x4 LWB 350 V-8 Was sm465-now 350TH/np205 Tilt, Tach, Towhooks Original Truck AM/FM Wellington, Ks



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