06-23-2008, 12:36 PM | #1 |
Damn Yankee
Join Date: Feb 2007
Location: Lynchburg, VA
Posts: 2,261
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12 bolt rear question
I've got a '68 12 bolt rear (6 lug) and a potential issue with alignment with the rest of the drivetrain. The center of the pinion is offset 1" towards passengers side; is this the way it should be? Do you angle the motor and trans to line up with it that way? I'm worried about the driveshaft being too close to the ECE crossmember
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06-23-2008, 06:39 PM | #2 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: 12 bolt rear question
that's how they were built.
This is to ensure the U joints are turned a little bit regardless of how loaded it is. If you roll with it loaded to max capacity all the time (farmers/lawn care guys/scrappers) then the U joint would not be angled up and down, so they offset it so the bearings would not stay in the same place. If they don't move around, they dig into the U joint metal causing failure pretty quick. |
06-24-2008, 05:50 AM | #3 | |
Damn Yankee
Join Date: Feb 2007
Location: Lynchburg, VA
Posts: 2,261
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Re: 12 bolt rear question
Quote:
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06-24-2008, 10:52 PM | #4 |
Registered User
Join Date: May 2008
Location: Waukesha, WI
Posts: 4
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Re: 12 bolt rear question
I have the same issue with my '67 short narrow bed pickup. It has a '71 leaf spring frame under it. I am going to have the rearend narrowed to get the pinion right in the center of the frame rails. The pinion angle will then be set by rotating the pinion down to achieve the right angle. Narrowing the rearend will also allow me to put on much larger tires.
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06-24-2008, 11:57 PM | #5 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: 12 bolt rear question
hey guy, you better talk to a drive line shop, or a shop that sets up prostreet suspentions. Altering the pinion angle chainges the way the truck would hook up.
It is offset for a reason. |
06-25-2008, 01:01 AM | #6 |
Hollister Road Co.
Join Date: Apr 2005
Location: Houston
Posts: 6,134
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Re: 12 bolt rear question
I had my rear narrowed and pinion centered and had to re-engineer the Tri-bar setup to work with it and I had to have axles made. It was costly and a PIA.
The original intent by GM for an offset rear was to save on axle manufacturing. One axle fits both sides so less machine tooling and fewer inventories saved them big bucks. Center the engine as you would a pinion centered rear. The advantage of centering the pinion is you get rid of the compound angle in the driveline. If you’re racing that becomes an issue. If not I'd leave it offset. It’s worked fine for however many years it’s been in use and you save the expense of axles and chopping the rear. Take a look at this link it may be helpful in lining up your drive train. http://www.thehollisterroadcompany.com/framesquare.html |
06-25-2008, 10:11 AM | #7 |
Registered User
Join Date: May 2008
Location: Waukesha, WI
Posts: 4
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Re: 12 bolt rear question
I have consulted a race car shop and centering the pinion was their recommendation. I do expect to take the truck to the dragstrip every now and then. It makes 450 horsepower and 470 lb ft of torque now. I plan to add some sort of power adder later to increase to 550-600 horsepower. I don't want to have any problems with the driveshaft so I want to get it straight now. I am very early into this project so making changes now is easy.
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