12 bolt rear end question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

shipma3 · 04-18-2013, 05:03 PM

kay i just got a 12 bolt truck rear end out of a 1980 chevy k10, but it says it had the gt4 option on the rear end what does this mean?

b454rat · 04-18-2013, 06:21 PM

1980 would be a 10 bolt I think. But anyways GT4 is 3.73

**Captainfab** · 04-19-2013, 12:02 AM

I agree. The original rear differential in a 1980 K10 should be a 8.5" 10 bolt. The last year for the 12 bolt in the K series was '79. In the C series trucks they were available thru '82.

shipma3 · 04-19-2013, 03:30 AM

weird this one is a 12 bolt out of an 1980 k10 lol i counted the bolts on the diff cover and it is a 12 bolt so i assume a 1980 12 bolt is pretty rare then and the vin on the receipt for the part does match for a 1980

crazy longhorn · 04-19-2013, 06:00 PM

Through 1982 on the 12 bolt....some apps may have been 10 bolt, but 82 was the last yr on the 12 bolt ? My sources show me this, & yes it is a 3.73 gear.....but is it a "gov bomb" , or a good eaton clutch posi? Shoot a pic , if you can

crazyL

**Captainfab** · 04-19-2013, 11:35 PM

It could quite possibly be an early production 1980.

I don't have my RPO code list here, to look up what GT4 says, but I do know that the RPO code for a Gov-Lock is G80

b454rat · 04-20-2013, 08:35 AM

I know GT4 is 3.73, GT5 is 4.10, GU6 is 3.42, I can go on!!!!! G80 is the code for locking diff, but anything late 70s and up won't have the clutch type posi. Only G and I think they are B bodies (Caprice, Impala LeSabre) will have clutch type posi. I look all the time in junkyards for rears and posi's and such, scary, I even know some Ferd stuff.....But just do a google for RPO codes, probly half million of them out there...

shipma2 · 04-21-2013, 02:30 AM

it's not a posi lol it's a average run of the mill 12 bolt from the wrecking yard pulled from underneath a 1980 k10. the receipt i got from the wrecker gave me the vin number and i checked it and it conformed to a 1980 k10

motornut · 04-23-2013, 01:06 PM

my 79 Jimmy has RPO 1HE4 is a G80 and it's 3.4

04-18-2013, 05:03 PM	#1
shipma3 Registered User Join Date: Mar 2012 Location: manti utah Posts: 67	12 bolt rear end question kay i just got a 12 bolt truck rear end out of a 1980 chevy k10, but it says it had the gt4 option on the rear end what does this mean?

04-18-2013, 06:21 PM	#2
b454rat Senior Member Join Date: May 2004 Location: Binghamton, NY Posts: 3,464	Re: 12 bolt rear end question 1980 would be a 10 bolt I think. But anyways GT4 is 3.73 __________________ 2000 GMC CCSB 454/4L80 6” lift SAS 1999 Chevy CCSB 454/NV4500 4” SAS 1999 GMC Yukon 350/4L60 6" SAS

04-19-2013, 12:02 AM	#3
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,250	Re: 12 bolt rear end question I agree. The original rear differential in a 1980 K10 should be a 8.5" 10 bolt. The last year for the 12 bolt in the K series was '79. In the C series trucks they were available thru '82. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

04-19-2013, 03:30 AM	#4
shipma3 Registered User Join Date: Mar 2012 Location: manti utah Posts: 67	Re: 12 bolt rear end question weird this one is a 12 bolt out of an 1980 k10 lol i counted the bolts on the diff cover and it is a 12 bolt so i assume a 1980 12 bolt is pretty rare then and the vin on the receipt for the part does match for a 1980

04-19-2013, 06:00 PM	#5
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	Re: 12 bolt rear end question Through 1982 on the 12 bolt....some apps may have been 10 bolt, but 82 was the last yr on the 12 bolt ? My sources show me this, & yes it is a 3.73 gear.....but is it a "gov bomb" , or a good eaton clutch posi? Shoot a pic , if you can crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

04-19-2013, 11:35 PM	#6
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,250	Re: 12 bolt rear end question It could quite possibly be an early production 1980. I don't have my RPO code list here, to look up what GT4 says, but I do know that the RPO code for a Gov-Lock is G80 __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

04-20-2013, 08:35 AM	#7
b454rat Senior Member Join Date: May 2004 Location: Binghamton, NY Posts: 3,464	Re: 12 bolt rear end question I know GT4 is 3.73, GT5 is 4.10, GU6 is 3.42, I can go on!!!!! G80 is the code for locking diff, but anything late 70s and up won't have the clutch type posi. Only G and I think they are B bodies (Caprice, Impala LeSabre) will have clutch type posi. I look all the time in junkyards for rears and posi's and such, scary, I even know some Ferd stuff.....But just do a google for RPO codes, probly half million of them out there... __________________ 2000 GMC CCSB 454/4L80 6” lift SAS 1999 Chevy CCSB 454/NV4500 4” SAS 1999 GMC Yukon 350/4L60 6" SAS

04-21-2013, 02:30 AM	#8
shipma2 Registered User Join Date: Aug 2011 Location: manti utah Posts: 95	Re: 12 bolt rear end question it's not a posi lol it's a average run of the mill 12 bolt from the wrecking yard pulled from underneath a 1980 k10. the receipt i got from the wrecker gave me the vin number and i checked it and it conformed to a 1980 k10

04-23-2013, 01:06 PM	#9
motornut 78K & 79C Jimmys Join Date: Nov 2009 Location: Ottawa Ont CANADA Posts: 7,901	Re: 12 bolt rear end question my 79 Jimmy has RPO 1HE4 is a G80 and it's 3.4 __________________ John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350



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