HOW to ID an AXLE ratio ?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GARMCo · 05-18-2004, 12:02 AM

My 73 K5 window sticker says it has "Optional Axle Ratio" with an RPO of "1ZN8" (or "ZN8"). I know there are several websites that have pretty comprehensive RPO code listings, but I have never found anything on this RPO--can anyone help me figure out what axle ratio I have (without doing the tire size/rpm/mph math) ??? Thanks !

jason952 · 05-18-2004, 10:28 AM

just jack up on wheel and spin it 2 revolutions and count the driveshaft turns. that's without posi

if you have posi, jack up both wheels and spin one revolution.

you'll know that you have posi if you can't spin the one wheel when you have it jacked.

**swervin ervin** · 05-18-2004, 10:45 AM

On the axle tube, passenger side, front, out about 6" from the center section, there should be a die punched code. It's real hard to find sometimes. The letters are small, about 1/8" in size. You will need to clean it off real good to find them. When you find them, post back here and I'll check the code for you.

Grim Reaper · 05-18-2004, 10:54 AM

Odd...it doesn't say what the ratio is after it? I thought if it had anything other then the stock gear it listed the RPO AND the ratio. My 79 Showed it had the 3.73.

If it's a factoy v8 the 3.73 is usualy the otion gear and if it's a I6 4.10 is the option gear. Your truck being a 73 HAD a tag on one of the cover bolt on that D44 in the front. See if it's still there.

I'm coming up blank on the code. Most Z RPO's have to do with appearance packages and Paint info like two tone.

1969 GMC · 05-18-2004, 02:47 PM

Quote:

Originally Posted by swervin ervin

On the axle tube, passenger side, front, out about 6" from the center section, there should be a die punched code. It's real hard to find sometimes. The letters are small, about 1/8" in size. You will need to clean it off real good to find them. When you find them, post back here and I'll check the code for you.

Here is where the numbers swervin is talking about will be located. It is called the Bill of Material number, or BOM. Usually you cannot see them, you will have to use a piece of sandpaper and some WD-40 to make them show up good.

05-18-2004, 12:02 AM	#1
GARMCo Registered User Join Date: May 2004 Location: Georgia Posts: 43	HOW to ID an AXLE ratio ?? My 73 K5 window sticker says it has "Optional Axle Ratio" with an RPO of "1ZN8" (or "ZN8"). I know there are several websites that have pretty comprehensive RPO code listings, but I have never found anything on this RPO--can anyone help me figure out what axle ratio I have (without doing the tire size/rpm/mph math) ??? Thanks !

05-18-2004, 10:45 AM	#3
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	On the axle tube, passenger side, front, out about 6" from the center section, there should be a die punched code. It's real hard to find sometimes. The letters are small, about 1/8" in size. You will need to clean it off real good to find them. When you find them, post back here and I'll check the code for you. __________________ Mike 1985 Chevy C-10

05-18-2004, 10:54 AM	#4
Grim Reaper Registered User Join Date: Jul 2001 Location: Atlanta GA Posts: 1,704	Odd...it doesn't say what the ratio is after it? I thought if it had anything other then the stock gear it listed the RPO AND the ratio. My 79 Showed it had the 3.73. If it's a factoy v8 the 3.73 is usualy the otion gear and if it's a I6 4.10 is the option gear. Your truck being a 73 HAD a tag on one of the cover bolt on that D44 in the front. See if it's still there. I'm coming up blank on the code. Most Z RPO's have to do with appearance packages and Paint info like two tone. __________________ Grim-Reaper 70 Pontiac LeMans Sport Convertible, worlds longest resto in progress Looking for 71-72 2wd Blazer or Jimmy Project

05-18-2004, 10:28 AM	#2
jason952 Registered User Join Date: Mar 2004 Posts: 65	just jack up on wheel and spin it 2 revolutions and count the driveshaft turns. that's without posi if you have posi, jack up both wheels and spin one revolution. you'll know that you have posi if you can't spin the one wheel when you have it jacked.



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