12 bolt rear end? same/same ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Ironhorse** · 02-17-2003, 09:43 PM

Curious as to the truck 12 bolt rear ends and car 12 bolt rear ends. Are they interchaneable, such as a 71 truck 5 lug rear end to say a 71 Chevelle 5 lug rear end? I'm not really sure if I am asking the correct question. Would a posi or open unit from a 3:73 truck fit into the axle housing on a 71 Chevelle? How do I tell what rear ratio is, truck has no engine/trans. but rear axle is complete. Is there an axle code I should be looking for and where? Any help is appreciated.

CustomChevy · 02-17-2003, 11:24 PM

car and truck rear ends are not the same. main difference is rear suspension. trucks mostly use leaf springs. cars mainly use coils. you would have to change mounts. you also have to check overall length of unit, cars are usually a little shorter.

hope this helps.
good luck!

*1FaastC10* · 02-18-2003, 12:19 AM

he's talking about internal components... and as for the vintage of trucks he's talking about... they have coil springs more commonly than leafs.

*Shane* · 02-18-2003, 12:23 AM

I may be wrong here, but I don't think the internals are the same size ... the car rear ends have a smaller ring gear ...

crazy longhorn · 02-18-2003, 09:07 AM

The ring gears are both 8 7/8" for car or truck 12 bolt, but wont interchange. The wild part is the car diff is actually stouter than the truck! The pinion stem on the car is 1.626 diameter , & the truck is 1.439. If you have a complete car rear diff, you might do a little measure on lenght, & possibly think about welding some pads & track locator brcaket on to use it under the truck. None of the internals will swap between the car & truck diffs tho..... crazyL

*Shane* · 02-18-2003, 11:27 AM

I stand corrected! LOL

Listen to crazy longhorn ... he knows his stuff ....

**Ironhorse** · 02-18-2003, 07:07 PM

Thanks for the info guys, figures that the rear ends won't interchange. Thought I might have lucked out and found a good rear gear to put in my 71 Chevelle SS. Oh well, guess I need to keep looking. Thanks for the help.

02-17-2003, 09:43 PM	#1
Ironhorse Senior Member Join Date: Jul 2001 Location: Wellington, Ks Posts: 10,094	12 bolt rear end? same/same ? Curious as to the truck 12 bolt rear ends and car 12 bolt rear ends. Are they interchaneable, such as a 71 truck 5 lug rear end to say a 71 Chevelle 5 lug rear end? I'm not really sure if I am asking the correct question. Would a posi or open unit from a 3:73 truck fit into the axle housing on a 71 Chevelle? How do I tell what rear ratio is, truck has no engine/trans. but rear axle is complete. Is there an axle code I should be looking for and where? Any help is appreciated. __________________ 1971 Chevy 1/2T 4x4 LWB 350 V-8 Was sm465-now 350TH/np205 Tilt, Tach, Towhooks Original Truck AM/FM Wellington, Ks

02-18-2003, 12:23 AM	#4
Shane Account Suspended Join Date: Jun 2000 Location: over yonder Posts: 14,270	I may be wrong here, but I don't think the internals are the same size ... the car rear ends have a smaller ring gear ... Last edited by Shane; 02-18-2003 at 11:29 AM.

02-18-2003, 09:07 AM	#5
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	The ring gears are both 8 7/8" for car or truck 12 bolt, but wont interchange. The wild part is the car diff is actually stouter than the truck! The pinion stem on the car is 1.626 diameter , & the truck is 1.439. If you have a complete car rear diff, you might do a little measure on lenght, & possibly think about welding some pads & track locator brcaket on to use it under the truck. None of the internals will swap between the car & truck diffs tho..... 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....

02-18-2003, 07:07 PM	#7
Ironhorse Senior Member Join Date: Jul 2001 Location: Wellington, Ks Posts: 10,094	Thanks for the info guys, figures that the rear ends won't interchange. Thought I might have lucked out and found a good rear gear to put in my 71 Chevelle SS. Oh well, guess I need to keep looking. Thanks for the help. __________________ 1971 Chevy 1/2T 4x4 LWB 350 V-8 Was sm465-now 350TH/np205 Tilt, Tach, Towhooks Original Truck AM/FM Wellington, Ks

02-17-2003, 11:24 PM	#2
CustomChevy Registered User Join Date: Nov 2002 Posts: 462	car and truck rear ends are not the same. main difference is rear suspension. trucks mostly use leaf springs. cars mainly use coils. you would have to change mounts. you also have to check overall length of unit, cars are usually a little shorter. hope this helps. good luck!

02-18-2003, 12:19 AM	#3
1FaastC10 Account Suspended Join Date: Oct 2002 Location: Elkhart, IN Posts: 6,400	he's talking about internal components... and as for the vintage of trucks he's talking about... they have coil springs more commonly than leafs.

02-18-2003, 11:27 AM	#6
Shane Account Suspended Join Date: Jun 2000 Location: over yonder Posts: 14,270	I stand corrected! LOL Listen to crazy longhorn ... he knows his stuff ....



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