Help with Axle / Differential identification. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

thefivejs1 · 01-29-2021, 11:12 PM

Looking for information on the differential information for this 12 bolt. We just installed a 430 hp crate motor to a TH350 Transmission and want to investigate a gear package. You opinions, experience and advice is appreciated.

BigBird05 · 01-30-2021, 10:40 AM

Look for the factory numbers on the front of the RH axle tube.

**LockDoc** · 01-30-2021, 10:46 AM

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Here are the charts.

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

Posts #8 & 19 show the locations for some of the code stampings.

LockDoc

**Accelo** · 01-31-2021, 11:39 AM

You need to know the installed gear ratio to identify the carrier series.
And if it's a posi or not.
Even with the stamping code it's not a guarantee it what you will have.
I would pull the cover and count the teeth and see what's there.

Truck 12 Bolt
Series 2 = 2.73 - down (smaller numerically)
Series 3 = 2.76 - 3.42
Series 4 = 3.73 - up (larger numerically)

**truckster** · 01-31-2021, 12:03 PM

Your best bet is to remove that rear cover and see what's actually in there. Unless you've owned the truck since it was new, there's a chance it's been swapped. And any rear end deserves fresh gear oil if you're going to put 430 HP into it.

01-29-2021, 11:12 PM	#1
thefivejs1 Registered User Join Date: Jan 2009 Location: Olathe, Kansas Posts: 6	Help with Axle / Differential identification. Looking for information on the differential information for this 12 bolt. We just installed a 430 hp crate motor to a TH350 Transmission and want to investigate a gear package. You opinions, experience and advice is appreciated. Attached Images

01-30-2021, 10:40 AM	#2
BigBird05 Registered User Join Date: Aug 2019 Location: Cheraw Posts: 1,300	Re: Help with Axle / Differential identification. Look for the factory numbers on the front of the RH axle tube.

01-30-2021, 10:46 AM	#3
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,771	Re: Help with Axle / Differential identification. - Here are the charts. http://67-72chevytrucks.com/vboard/s...d.php?t=578793 Posts #8 & 19 show the locations for some of the code stampings. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

01-31-2021, 11:39 AM	#4
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,295	Re: Help with Axle / Differential identification. You need to know the installed gear ratio to identify the carrier series. And if it's a posi or not. Even with the stamping code it's not a guarantee it what you will have. I would pull the cover and count the teeth and see what's there. Truck 12 Bolt Series 2 = 2.73 - down (smaller numerically) Series 3 = 2.76 - 3.42 Series 4 = 3.73 - up (larger numerically)

01-31-2021, 12:03 PM	#5
truckster Senior Member Join Date: Jan 2001 Location: Orem, Utah Posts: 7,976	Re: Help with Axle / Differential identification. Your best bet is to remove that rear cover and see what's actually in there. Unless you've owned the truck since it was new, there's a chance it's been swapped. And any rear end deserves fresh gear oil if you're going to put 430 HP into it. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson



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