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

aggie91 · 07-05-2022, 02:34 PM

Well guys I ran into a new one for me...

I have a '73 (per the title, '74 per the VIN) Suburban that I picked up and did some investigation on the rear axle for servicing it. It turns out it is a 3.07 gear with a factory LSD carrier and the pinion yoke takes a 1330 series U-Joint. The ring gear is stamped 14 43, which works out to a 3.071428571 ratio.

I also have another 12 bolt from a square body (not 100% sure what it originally was in before I got it). It is has 3.07 gears and an open carrier. The pinion yoke on this one takes a 1310 series U-Joint. The ring gear is stamped 15 46, which works out to a 3.066666667 ratio.

All the other 12 bolts that I have and have had in the past have the same pinion yoke size that uses the 1310 u-joint.

Has anyone else seen 12 bolts with the same ratio, but different tooth counts and a different pinion yoke?

Would GM make multiple sets of gears that work out to the same ratio for the same type of axle? What would be the reason to do so?

**Warrens69GMC** · 07-05-2022, 09:39 PM

Probably the year manufactured has something to do with it. The early 74 may have had the R&P from a earlier run, and there could lie the discrepancy.

SunSoaked · 07-05-2022, 11:17 PM

Get a 14 bolt and pat yourself on the back.

aggie91 · 07-06-2022, 08:30 AM

Quote:

Originally Posted by SunSoaked

Get a 14 bolt and pat yourself on the back.

Why? That is not really an option since it is WAY overkill for the intended use.

Also, it would cost me $$ to get one when I already have a good useable rear axle.

aggie91 · 07-06-2022, 08:32 AM

Quote:

Originally Posted by Warrens69GMC

Probably the year manufactured has something to do with it. The early 74 may have had the R&P from a earlier run, and there could lie the discrepancy.

I am going to dig into the year manufactured also, but so far from what I have seen, the pinion yoke difference may be do to the fact that the original engine in the suburban was a 454. I have read that those had the 1330 style u-joints...

**Warrens69GMC** · 07-06-2022, 09:11 AM

Curious to see what you find out. I have a 1979 Suburban with a 454/TH400/3.73 open in my yard.

07-05-2022, 02:34 PM	#1
aggie91 I'm just glad to be here! Join Date: Jan 2008 Location: Longview, TX Posts: 4,788	12 bolt rear axles Well guys I ran into a new one for me... I have a '73 (per the title, '74 per the VIN) Suburban that I picked up and did some investigation on the rear axle for servicing it. It turns out it is a 3.07 gear with a factory LSD carrier and the pinion yoke takes a 1330 series U-Joint. The ring gear is stamped 14 43, which works out to a 3.071428571 ratio. I also have another 12 bolt from a square body (not 100% sure what it originally was in before I got it). It is has 3.07 gears and an open carrier. The pinion yoke on this one takes a 1310 series U-Joint. The ring gear is stamped 15 46, which works out to a 3.066666667 ratio. All the other 12 bolts that I have and have had in the past have the same pinion yoke size that uses the 1310 u-joint. Has anyone else seen 12 bolts with the same ratio, but different tooth counts and a different pinion yoke? Would GM make multiple sets of gears that work out to the same ratio for the same type of axle? What would be the reason to do so? __________________ Karl 1965 Chevy Stepside(Grandpa's Old Blue) and (July 2015 Shop Build!)(2020, the Saga Continues) http://67-72chevytrucks.com/vboard/s...d.php?t=372424 The LST Challenge: http://67-72chevytrucks.com/vboard/s...=1#post7812257 Korbin's 1st Square: "Sunburn" http://67-72chevytrucks.com/vboard/s...d.php?t=418618 1985 GMC Sierra: "White Trash", Korbin's 2nd now... http://67-72chevytrucks.com/vboard/s...d.php?t=632305 Henry - 1984 Chevrolet, Owen's 1st Square

07-05-2022, 09:39 PM	#2
Warrens69GMC Registered User Join Date: Jan 2003 Location: Safford,AZ Posts: 3,625	Re: 12 bolt rear axles Probably the year manufactured has something to do with it. The early 74 may have had the R&P from a earlier run, and there could lie the discrepancy. __________________ 1969 307, t350 1950 Chevy Wagon 1978 Big 10 1967 C10, 250,3-OTT

07-05-2022, 11:17 PM	#3
SunSoaked Registered User Join Date: Dec 2011 Location: Yuma Arizona Posts: 1,525	Re: 12 bolt rear axles Get a 14 bolt and pat yourself on the back.

07-06-2022, 09:11 AM	#6
Warrens69GMC Registered User Join Date: Jan 2003 Location: Safford,AZ Posts: 3,625	Re: 12 bolt rear axles Curious to see what you find out. I have a 1979 Suburban with a 454/TH400/3.73 open in my yard. __________________ 1969 307, t350 1950 Chevy Wagon 1978 Big 10 1967 C10, 250,3-OTT

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