Rear axle decode and gear ratio? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mikes66ChevyC10 · 10-03-2014, 08:19 PM

Can anybody decode my rear axle code? It's HA 06 2 1 W

Also I tried checking the gear ratio by spinning one rear tire and watching how many times the driveshaft yoke went around and with one complete turn of the tire the driveshaft only went around a little less than 2 turns? Does that sound right?

geezer#99 · 10-03-2014, 10:31 PM

A little less than 2 times needs to be doubled.
Likely a 3.73 gear.

jtrichard · 10-03-2014, 10:58 PM

one wheel on the ground two turns on the other wheel will give you a more accurate result.... if you then get 3 and 3/4 turns on the drive shaft then you have 3.73 ....4+ a little would be 4.10

**Captainfab** · 10-03-2014, 11:03 PM

The HA code 12 bolt originally came with 3.73 gears. But that was aprox 50 years ago. Why not just pull the cover and have a look. I almost guarantee that the oil needs changed. It'll just cost you a cover gasket, a couple quarts of gear oil and a little time. Then you'll know exactly what gears you have and the peace of mind knowing that your differential has fresh oil and what the condition is inside.

Mikes66ChevyC10 · 10-04-2014, 05:13 PM

Thanks for the reply's guys!! The main reason I was asking to have the axle code decoded was to see if the rear end is the original rear for the truck so I know when I go to order parts. I'm planning a 5 lug/disk brake conversion along with an Eaton limited slip differential, and new gears. Would the code tell you if it's from a 66 C10?

I know the original owner of my truck replaced the granny gear trans for a late 70's 3spd so I'm not sure what else he changed.

AnlaufJohn · 10-04-2014, 06:43 PM

I agree with Captainfab and suggest pulling the rear cover off.
You may discover your rear end has limited slip, too.
The banging noise I chased for 2 years was solved when my mechanic pulled the cover off and yelled out to me, "Do you know you have posi-trac?"

**aerotruk63** · 10-04-2014, 08:09 PM

As the Captain said.

Mikes66ChevyC10 · 10-04-2014, 08:44 PM

Thanks for your help! Took the diff cover off and it does have the 3.73's and of course the fluid is shot. It doesn't have the limited slip diff. Going to do a full rebuild on the rear end after I get the cab done.

Lugnutz65 · 10-04-2014, 11:21 PM

Here's mine. It's a 3.73. I confirmed by pulling the cover and prior to that by spinning the tire a full 10 revolutions.

10-03-2014, 08:19 PM	#1
Mikes66ChevyC10 Registered User Join Date: Feb 2014 Location: Forest City PA Posts: 378	Rear axle decode and gear ratio? Can anybody decode my rear axle code? It's HA 06 2 1 W Also I tried checking the gear ratio by spinning one rear tire and watching how many times the driveshaft yoke went around and with one complete turn of the tire the driveshaft only went around a little less than 2 turns? Does that sound right? __________________ 1966 C10 Stepside swb http://67-72chevytrucks.com/vboard/s...d.php?t=617778

10-03-2014, 10:31 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,733	Re: Rear axle decode and gear ratio? A little less than 2 times needs to be doubled. Likely a 3.73 gear.

10-03-2014, 10:58 PM	#3
jtrichard Registered User Join Date: Jun 2013 Location: joshua tree ca. Posts: 1,484	Re: Rear axle decode and gear ratio? one wheel on the ground two turns on the other wheel will give you a more accurate result.... if you then get 3 and 3/4 turns on the drive shaft then you have 3.73 ....4+ a little would be 4.10

10-03-2014, 11:03 PM	#4
Captainfab 60-66 Nut Join Date: Mar 2007 Location: Coeur d'Alene, Idaho Posts: 23,252	Re: Rear axle decode and gear ratio? The HA code 12 bolt originally came with 3.73 gears. But that was aprox 50 years ago. Why not just pull the cover and have a look. I almost guarantee that the oil needs changed. It'll just cost you a cover gasket, a couple quarts of gear oil and a little time. Then you'll know exactly what gears you have and the peace of mind knowing that your differential has fresh oil and what the condition is inside. __________________ Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE

10-04-2014, 05:13 PM	#5
Mikes66ChevyC10 Registered User Join Date: Feb 2014 Location: Forest City PA Posts: 378	Re: Rear axle decode and gear ratio? Thanks for the reply's guys!! The main reason I was asking to have the axle code decoded was to see if the rear end is the original rear for the truck so I know when I go to order parts. I'm planning a 5 lug/disk brake conversion along with an Eaton limited slip differential, and new gears. Would the code tell you if it's from a 66 C10? I know the original owner of my truck replaced the granny gear trans for a late 70's 3spd so I'm not sure what else he changed. __________________ 1966 C10 Stepside swb http://67-72chevytrucks.com/vboard/s...d.php?t=617778

10-04-2014, 06:43 PM	#6
AnlaufJohn Registered User Join Date: Feb 2009 Location: Lebanon, Oregon Posts: 130	Re: Rear axle decode and gear ratio? I agree with Captainfab and suggest pulling the rear cover off. You may discover your rear end has limited slip, too. The banging noise I chased for 2 years was solved when my mechanic pulled the cover off and yelled out to me, "Do you know you have posi-trac?" __________________ Eugene, Oregon Lucy's Limousine 1966 C-10 LWB 283 w/ 2bbl, OE carb and dist. 4 spd (granny 1st) w/ 3.73 rear end

10-04-2014, 08:09 PM	#7
aerotruk63 Check The Champ, Demonstrator Join Date: Jun 2009 Location: Montreal,Quebec Posts: 6,627	Re: Rear axle decode and gear ratio? As the Captain said. __________________ 1963 *Chevrolet Truck* Literature LINK: https://picasaweb.google.com/113840717762774560215 YouTube Channel with 20+ Original *Chevrolet Truck* Salesmen, Mechanics & Service Department Training Slideshows. https://www.youtube.com/results?sear...otruk63&page=1

10-04-2014, 08:44 PM	#8
Mikes66ChevyC10 Registered User Join Date: Feb 2014 Location: Forest City PA Posts: 378	Re: Rear axle decode and gear ratio? Thanks for your help! Took the diff cover off and it does have the 3.73's and of course the fluid is shot. It doesn't have the limited slip diff. Going to do a full rebuild on the rear end after I get the cab done. __________________ 1966 C10 Stepside swb http://67-72chevytrucks.com/vboard/s...d.php?t=617778

10-04-2014, 11:21 PM	#9
Lugnutz65 Registered User Join Date: Jan 2013 Location: Columbia, SC Posts: 1,927	Re: Rear axle decode and gear ratio? Here's mine. It's a 3.73. I confirmed by pulling the cover and prior to that by spinning the tire a full 10 revolutions. Attached Images __________________ My 65 C10 build: www.lugnutz65chevystepside.weebly.com Want to know more about T5 transmissions? My website has a T5 Info Page and a Step by Step T5 rebuild.

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