12 bolt questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rauto13 · 09-29-2005, 06:24 PM

I am wanting to shorten a 12 bolt rear end for bigger tires. First can this be done? I know the axle tubes would have to cut and rewelded. I am wondering if the axles can be shortened and what is involved in this? Are the axles a straight splined shaft or tapered splined shaft?

If the axles cannot be shortened, can I get custom length axles? About how much are they? Can I get them any length I need?

Thanks for the help.

69 longhorn · 09-30-2005, 08:59 AM

You can shorten the housing, but can not respline the stock axles(they are tapered behind the spline, as you have figured). You can get custom lenght axles to fit (try Moser engineering).......with that said, you may be better off running a custom backspace on your wheels to fit the rubber that you want. I havent done this myself, but understand that you can fit a 15x12, or 15x14 wheel on a coil spring truck(mini tub, & proper backspace). You might ask board member SCOTTI about his setup.......69L

1969 C/K CST · 09-30-2005, 09:07 AM

There are also others that will take cores. Just food for thought. http://www.drivetrain.com/rearend.html

djracer · 09-30-2005, 11:03 AM

Buy all of my 9 inch stuff unless you are just building it for looks! The 12 bolt is a little weak. I have every piece of a really nice 9 inch for sale!

http://67-72chevytrucks.com/vboard/s...31#post1424931

thejoker · 09-30-2005, 11:08 AM

Can't speak from experience but was told by a racer he used a S-10 4X4 rear end. He says the axles are much stronger in the 4X4 so they will handle the torture from a high performance engine and from the extra rubber on the street. He had to do a little welding but it looked great and he was right it handle the 400+ hp he was putting to it.

DP

mplex2000 · 09-30-2005, 11:39 AM

12 bolts rock, a little less drivetrain power loss than a 9 inch.

If you're going to narrow it, now is the perfect time to have Ford housing ends welded on since you'll be getting new axles anyway. Get rid of those C clips, the only bad thing about GM rear ends.

Also gives a lot of options for inexpensive rear disc brakes.

69 longhorn · 09-30-2005, 12:36 PM

On the street, you wont have any troubles with the 12 bolt truck rear, but for all out drag racing, they are a little weak. for that app, you might look at the 12 bolt (car diff), or the most commonly used 9" Ferd. the ford rear is much easier to set up,& work on(drop out center ), no c clips, ect.....it does take a little more power to run due to how far below the axle centerline that the pinion is placed tho.... I have been pounding a 12 bolt on the street for a dozen yrs or so(currently with a mild 383), but she has seen some guff from a warmed up 455 Olds,& I have broken nothing . they have to hook up to break the pcs(all i got was rubber smoke).....

L

mplex2000 · 09-30-2005, 02:03 PM

The 12 bolt's only real weakness is the c clips. Once those are gone it's just as strong as a 9 inch (if not, close enough - I doubt anybody here will be building a truck with enough power and traction to break one).

cdowns · 09-30-2005, 02:28 PM

it's really not worth the expense to shorten the axel anything more than a couple of inches on each side will require dumping the trailing arms i ran 12"rims with 5"backspace with no clearance issues

70c10swb · 09-30-2005, 05:41 PM

Quote:

Originally Posted by cdowns

it's really not worth the expense to shorten the axel anything more than a couple of inches on each side will require dumping the trailing arms i ran 12"rims with 5"backspace with no clearance issues

did they stick out at all? i want to run a 29x15.5 (12 inch wide rim) and i want them to tuck in the wells nicely.

09-29-2005, 06:24 PM	#1
rauto13 saving one more Join Date: Sep 2005 Location: Pryor Creek, Oklahoma Posts: 3,066	12 bolt questions I am wanting to shorten a 12 bolt rear end for bigger tires. First can this be done? I know the axle tubes would have to cut and rewelded. I am wondering if the axles can be shortened and what is involved in this? Are the axles a straight splined shaft or tapered splined shaft? If the axles cannot be shortened, can I get custom length axles? About how much are they? Can I get them any length I need? Thanks for the help. __________________ 72 Chevy longbed - now for parts 69 Chevy short fleet - needing some love 70 RS Camaro - needing more love driver - 96 GMC X-cab Last edited by rauto13; 09-29-2005 at 06:24 PM.

09-30-2005, 08:59 AM	#2
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	You can shorten the housing, but can not respline the stock axles(they are tapered behind the spline, as you have figured). You can get custom lenght axles to fit (try Moser engineering).......with that said, you may be better off running a custom backspace on your wheels to fit the rubber that you want. I havent done this myself, but understand that you can fit a 15x12, or 15x14 wheel on a coil spring truck(mini tub, & proper backspace). You might ask board member SCOTTI about his setup.......69L __________________ http://community.webshots.com/user/hotrodhorn

09-30-2005, 09:07 AM	#3
1969 C/K CST A.K.A- Crummy Join Date: Jun 2005 Location: NC foothills Posts: 3,025	There are also others that will take cores. Just food for thought. http://www.drivetrain.com/rearend.html __________________ 2003 Silverado Z71 Are fishermen all liars?

09-30-2005, 11:03 AM	#4
djracer Registered User Join Date: Feb 2001 Location: Wetumpka, Al, U.S. Posts: 8,892	Buy all of my 9 inch stuff unless you are just building it for looks! The 12 bolt is a little weak. I have every piece of a really nice 9 inch for sale! http://67-72chevytrucks.com/vboard/s...31#post1424931 __________________ Kevin Special Thanks to All who have helped on the TRUCK! My Pass Time Show http://s129.photobucket.com/albums/p...Chapter1-0.mp4 So Far my best Times are: Motor only: 6.44 1/8 @ 104.13 10.39 1/4 @ 125.83 Nitrous Times: 5.785 1/8 @ 118.65 with a 1.336 60ft 9.168 1/4 @ 142.58 with a 250 shot dead out of the hole!

09-30-2005, 11:08 AM	#5
thejoker Registered User Join Date: Jun 2005 Location: Gulfport Mississippi Posts: 364	Can't speak from experience but was told by a racer he used a S-10 4X4 rear end. He says the axles are much stronger in the 4X4 so they will handle the torture from a high performance engine and from the extra rubber on the street. He had to do a little welding but it looked great and he was right it handle the 400+ hp he was putting to it. DP __________________ **Have you ever danced with the devil in the pale moonlight....I ask that of all my prey** 68' C10 Short Step (rebuilding as we speak) 72' Custom Camper (wrecked, parting out) 79' C10 Fleet (rough, parting out) 97' C1500 Short Step Custom (DD) 97' Kawaski VN800a Customized 99' Z71 Silverado 04' Suzuki Volusia

09-30-2005, 11:39 AM	#6
mplex2000 Registered User Join Date: Jul 2005 Location: DFW Posts: 463	12 bolts rock, a little less drivetrain power loss than a 9 inch. If you're going to narrow it, now is the perfect time to have Ford housing ends welded on since you'll be getting new axles anyway. Get rid of those C clips, the only bad thing about GM rear ends. Also gives a lot of options for inexpensive rear disc brakes.

09-30-2005, 12:36 PM	#7
69 longhorn Registered User Join Date: Aug 2001 Location: rock island,il,usa Posts: 5,382	On the street, you wont have any troubles with the 12 bolt truck rear, but for all out drag racing, they are a little weak. for that app, you might look at the 12 bolt (car diff), or the most commonly used 9" Ferd. the ford rear is much easier to set up,& work on(drop out center ), no c clips, ect.....it does take a little more power to run due to how far below the axle centerline that the pinion is placed tho.... I have been pounding a 12 bolt on the street for a dozen yrs or so(currently with a mild 383), but she has seen some guff from a warmed up 455 Olds,& I have broken nothing . they have to hook up to break the pcs(all i got was rubber smoke)..... L __________________ http://community.webshots.com/user/hotrodhorn

09-30-2005, 02:03 PM	#8
mplex2000 Registered User Join Date: Jul 2005 Location: DFW Posts: 463	The 12 bolt's only real weakness is the c clips. Once those are gone it's just as strong as a 9 inch (if not, close enough - I doubt anybody here will be building a truck with enough power and traction to break one).

09-30-2005, 02:28 PM	#9
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	it's really not worth the expense to shorten the axel anything more than a couple of inches on each side will require dumping the trailing arms i ran 12"rims with 5"backspace with no clearance issues __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY



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