# will 69' 12 bolt chevelle rear end fit 66' tempest



## Instg8ter (Sep 28, 2010)

have a chance to get a 12 bolt for a good price with 4:88 gears, aftermarket axles, long studs, C clip eliminators and new poly bushings. anyone tell me if this will fit and/or what mods might need to be done to make it work, last part i need to procure for my build 
s1098.photobucket.com/albums/g372/instg8ter/1966 Tempest/?start=0


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## BearGFR (Aug 25, 2008)

Instg8ter said:


> have a chance to get a 12 bolt for a good price with 4:88 gears, aftermarket axles, long studs, C clip eliminators and new poly bushings. anyone tell me if this will fit and/or what mods might need to be done to make it work, last part i need to procure for my build
> s1098.photobucket.com/albums/g372/instg8ter/1966 Tempest/?start=0


It'll be close. There are two main groups of A-body cars for things like this: 64-67, and 68-72. The rear your're asking about would definitely be a direct bolt in for a 68-72 car, but not an exact fit for a 66. The main differences between 64-67 rears and 68-72 rears are the length of the upper control arms, and the width of the axle "brake drum to brake drum". The spring perches, shock mounts, and lower control arms are the same. The upper control arm issue you can fix with adjustable upper control arms. The width issue might be more of a problem, the 68-72 unit is wider than the 64-67 unit by about 1 3/4" to 2", depending on who you believe. Since the 69 unit is wider than the 66 though, you might be able to adjust by using wheels with different back-spacing. You could also have a the axle tubes shortened to use 64-67 axles, but that'd be more expensive. If you're getting a really good deal on the 12 bolt, it's worth doing. I'd be concerned about the gear ratio though. 4.88 is mighty short for a Pontiac torque motor unless you're building a high-rpm 400 for drag racing only, and running tall tires. You'll also want to be meticulous about making sure your pinion angle is correct, otherwise you'll get a vibration in the driveshaft. That's what the adjustabe uppers are for.

Bear


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## jetstang (Nov 5, 2008)

It will bolt right in. But, it is 5/8" wider per side, so you can just get larger offset rims, 5" or so. You will need a conversion U joint for your driveshaft. Beyond that it will bolt right in. 4.88s are terrible for the street and 1/4 mile unless you have a high RPM motor. It will make the car quick up to 70 MPH. My old BBC pulled 3200 RPMs at 45 MPH in 4th gear w/4.88s.


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## Instg8ter (Sep 28, 2010)

thanks for the help, whats the lowest gear i can put in that stage three carries 3.73?


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## BearGFR (Aug 25, 2008)

Instg8ter said:


> thanks for the help, whats the lowest gear i can put in that stage three carries 3.73?


I'm not sure. Here's something else you might consider, though, depending on your budget and how you plan to use the car. If that 12-bolt really is a good deal, buy it then turn around and sell it for a profit. Apply the proceeds towards having a rear built for you. There are several vendors out there (Moser, Currie, etc.) that can custom build whatever you want. I had Moser build me a 9-inch Ford that was a bolt-in for my 69. They can also build 12-bolts and/or Dana 60's. I went with the 9-inch because 1) NHRA and other sanctioning bodies don't permit c-clip style axles, "eliminators" are required 2) c-clip eliminator kits aren't recommended for street use due to wear issues 3) the 9-inch is stronger 4) changing gear ratios in a 9-inch is simple and 5) I didn't care about keeping the car 'factory original'. It depends on what you want, how much power you're carrying, and how you plan to use/drive the car. The factory 10-bolt is adequate, if it's in good condition, unless you're around 500 ft.lbs or more and have the car set up so that it will hook really well, and plan to take advantage of that. 

Bear


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## geeteeohguy (Feb 2, 2008)

Really good info. With the ten bolts, (not the case here), I've found that the '66 up units are 1" wider than the '65 on back. The '67 unit I pulled from my '67 was replaced by a '69 unit, which was identical. On those 4.88's, it WIlLL get to 70mph very quickly, your top speed won't be much higher than that, either!! Good luck.


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> Really good info. With the ten bolts, (not the case here), I've found that the '66 up units are 1" wider than the '65 on back. The '67 unit I pulled from my '67 was replaced by a '69 unit, which was identical.


Upon further research, I found that 67 was a transition year. Early 67 production vehicles used the same rear as previous years, late 67 production vehicles used the same rear as 68 and up. I got bit by something similar on my 69 GTO with the water pump - early production models used pumps with a shorter snout than did late production models.

Bear


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## 05GTO (Oct 6, 2004)

Instg8ter said:


> thanks for the help, whats the lowest gear i can put in that stage three carries 3.73?


yes,

Three Series = 3.08:1 to 3.73:1,
Four Series = 3.90:1 to 6.14:1


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## melp (Dec 29, 2010)

*69 chevelle 12 bolt in 67 gto*

I just bought a 69 12 bolt also and plan to install in my 67 gto. Just wondering if you purchased the 12 bolt and have installed? 

Thanks


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## BearGFR (Aug 25, 2008)

melp said:


> I just bought a 69 12 bolt also and plan to install in my 67 gto. Just wondering if you purchased the 12 bolt and have installed?
> 
> Thanks


From what I've learned, it's important to know if you have an "early production" 67 or a "late production" 67. If you have a late production car, it will probably bolt right in.

Bear


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## geeteeohguy (Feb 2, 2008)

My '67 GTO was built in late '66....it is an early car. Yet, the original differential was exactly the same as the '69 unit I replaced it with. All A-body rears from '64-'72 will bolt in with no issues. The one inch difference in width of the axle tubes= 1/2 inch per side....undetectable. Go for it. From what I've seen, the '64-'65 rears are the narrow ones. The '66 rear ends are the same as the '72's in dimension.


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## BearGFR (Aug 25, 2008)

geeteeohguy said:


> My '67 GTO was built in late '66....it is an early car. Yet, the original differential was exactly the same as the '69 unit I replaced it with. All A-body rears from '64-'72 will bolt in with no issues. The one inch difference in width of the axle tubes= 1/2 inch per side....undetectable. Go for it. From what I've seen, the '64-'65 rears are the narrow ones. The '66 rear ends are the same as the '72's in dimension.


The word of someone who's actually done it is always better than the estimates of someone who hasn't :cheers

Bear


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## geeteeohguy (Feb 2, 2008)

Thanks, Bear. But when I'm ready to build a kick butt roller-stroker motor, I'm consulting YOU!!!! I've been around GTO's a long time, and have had a bunch of them, so I've BTDT with a lot of this "stuff". Still, it always amazes me at my lack of knowledge with a lot of the newer trends..... but that's part of what makes all of this so much fun. Never a dull moment! Everybody wins on this forum, IMO. A ton of trial and error is eliminated, and even more good information is shared. Have a great new year, and looking to see that '69 on the ROAD!!!!


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## melp (Dec 29, 2010)

*12 bolt in 67*

The rear end in my 67 was not the orginal, it had a 69 date code and measures the same as the 12 bolt so it shouldn't be a problem. Are the jokes different, will I need to change my u joint? I am hoping to get it back together in the next couple of days. Thanks so much for everyone's help.


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