How to identify what my gear ratio is? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Reziel_1983 · 03-25-2011, 12:34 AM

I have a 10 bolt rear end in my 83 c10 and I'm trying to figure out what my gear ratio is, can anyone let me know if there is some kind of number I can find on the rear end and type in somewhere on the web? or how I can figure out my gear ratio?

Thanks,

Reziel

Keith Seymore · 03-25-2011, 05:49 AM

The first thing to check is the SPID label in the glovebox. There may be an RPO code on the label (but not always) indicating which ratio the truck got when built. But - after all these years there are no guarantees that ratio is still in the truck.

The second way would be to rotate the tire[s] and see how many times the driveshaft goes around. There is a somewhat elaborate procedure to do this, depending on if you have a locking/limited slip differential. The guys here can explain in more detail if you need it.

The most surefire way is to pull the cover and count the number of teeth on the ring and pinion

K

7T2 · 03-25-2011, 08:52 AM

If you've got the rear cover off, there should be two numbers somewhere stamped into the ring gear. If you divide one into the other it will give you the gear ratio. For instance, 41:11 is a 3.73 ratio. 41 divided by 11 = 3.73

Reziel_1983 · 03-25-2011, 01:06 PM

Thanks guys

jrcaprai · 03-25-2011, 01:52 PM

The rotating the tires is not a very accurate way to check...

count the number of teeth on the pinion and count the number of teeth on the Ring Gear... divide the ring gear by the pinion.

example: 50 teeth on Ring gear ,divided by 15 teeth on Pinion = 3.33

Tx Firefighter · 03-25-2011, 05:43 PM

Rotating the tire method works fine. As far as accuracy, you've got 2.73, 3.08, 3.42, 3.73 and 4.11 common ratios. It's accurate enough to tell them apart.
Posted via Mobile Device

jrcaprai · 03-25-2011, 06:17 PM

Quote:

Originally Posted by Tx Firefighter

Rotating the tire method works fine. As far as accuracy, you've got 2.73, 3.08, 3.42, 3.73 and 4.11 common ratios. It's accurate enough to tell them apart.
Posted via Mobile Device

Different size tires will alter your results

*lakeroadster* · 03-25-2011, 06:27 PM

Quote:

Originally Posted by jrcaprai

Different size tires will alter your results

No it doesn't. One revolution is one revolution, regardless of tire size.

Follow this procedure, it always works when done properly:

To check rear end ratio jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. With the tranny in neutral (block the front tires first) rotate the jacked up tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

4x4toy · 03-25-2011, 06:33 PM

Pull the cover, its probably over due for a gear oil change anyway.

Leedogg · 03-25-2011, 06:35 PM

I am going to do the spin the pinion for the tire to spin 1 round first- then if that fails- pop the cover and count teeth.

edit...had it backwards..doh...was half asleep.

jrcaprai · 03-25-2011, 07:12 PM

Quote:

Originally Posted by lakeroadster

No it doesn't. One revolution is one revolution, regardless of tire size.

Follow this procedure, it always works when done properly:

To check rear end ratio jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. With the tranny in neutral (block the front tires first) rotate the jacked up tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

Your right... the tip of the second hand on a clock will go around the same as middle of the second hand will go around the same ... Doh !

rotgg · 03-25-2011, 09:09 PM

Quote:

Originally Posted by jrcaprai

Your right... the tip of the second hand on a clock will go around the same as middle of the second hand will go around the same ... Doh !

you just OWNED yourself lol

rotgg · 03-25-2011, 09:09 PM

Quote:

Originally Posted by Tx Firefighter

Rotating the tire method works fine. As far as accuracy, you've got 2.73, 3.08, 3.42, 3.73 and 4.11 common ratios. It's accurate enough to tell them apart.
Posted via Mobile Device

agree!!!!!!!!!!!!

jrcaprai · 03-25-2011, 09:26 PM

Quote:

Originally Posted by rotgg

you just OWNED yourself lol

It happens

rotgg · 03-25-2011, 09:27 PM

Quote:

Originally Posted by jrcaprai

It happens

i am sorry man i could not help it lol i am glad you understand the theory now

rayfinseats · 03-26-2011, 10:59 PM

Rotating the tire method works fine. As far as accuracy, you've got 2.73, 3.08, 3.42, 3.73 and 4.11 common ratios. It's accurate enough to tell them apart.

AGREE. I once had one that came out to 2.5. I thought I was on drugs. Pulled the cover and sure enough it was a 2.56. No wonder it took 1/2 a block to spin the tires.

03-25-2011, 12:34 AM	#1
Reziel_1983 Registered User Join Date: Feb 2011 Location: Brownwood, Texas Posts: 421	How to identify what my gear ratio is? I have a 10 bolt rear end in my 83 c10 and I'm trying to figure out what my gear ratio is, can anyone let me know if there is some kind of number I can find on the rear end and type in somewhere on the web? or how I can figure out my gear ratio? Thanks, Reziel __________________ 1983 Chevy lwb: 400 sbc destroked to 377, comp cams xe 268, Holley Street Dominator Intake, Holley Street Avenger 670 cfm, headers, flowmasters. SOLD 1998 Trans am, mostly stock with magnaflow catback My build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=454329

03-25-2011, 05:49 AM	#2
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,229	Re: How to identify what my gear ratio is? The first thing to check is the SPID label in the glovebox. There may be an RPO code on the label (but not always) indicating which ratio the truck got when built. But - after all these years there are no guarantees that ratio is still in the truck. The second way would be to rotate the tire[s] and see how many times the driveshaft goes around. There is a somewhat elaborate procedure to do this, depending on if you have a locking/limited slip differential. The guys here can explain in more detail if you need it. The most surefire way is to pull the cover and count the number of teeth on the ring and pinion K __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

03-25-2011, 08:52 AM	#3
7T2 Active Member Join Date: Dec 2004 Location: Marysville, OH Posts: 667	Re: How to identify what my gear ratio is? If you've got the rear cover off, there should be two numbers somewhere stamped into the ring gear. If you divide one into the other it will give you the gear ratio. For instance, 41:11 is a 3.73 ratio. 41 divided by 11 = 3.73 __________________ 1957 GMC Ambulance 1962 Belair Wagon 1963 C80 Truck Cab FOR SALE 1969 Chevy C10 Short Bed 1972 Chevy C10 Long Bed SOLD 1996 C3500 Dually SOLD

03-25-2011, 01:06 PM	#4
Reziel_1983 Registered User Join Date: Feb 2011 Location: Brownwood, Texas Posts: 421	Re: How to identify what my gear ratio is? Thanks guys __________________ 1983 Chevy lwb: 400 sbc destroked to 377, comp cams xe 268, Holley Street Dominator Intake, Holley Street Avenger 670 cfm, headers, flowmasters. SOLD 1998 Trans am, mostly stock with magnaflow catback My build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=454329

03-25-2011, 01:52 PM	#5
jrcaprai Registered User Join Date: May 2008 Location: Salt Lake City Posts: 365	Re: How to identify what my gear ratio is? The rotating the tires is not a very accurate way to check... count the number of teeth on the pinion and count the number of teeth on the Ring Gear... divide the ring gear by the pinion. example: 50 teeth on Ring gear ,divided by 15 teeth on Pinion = 3.33

03-25-2011, 05:43 PM	#6
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: How to identify what my gear ratio is? Rotating the tire method works fine. As far as accuracy, you've got 2.73, 3.08, 3.42, 3.73 and 4.11 common ratios. It's accurate enough to tell them apart. Posted via Mobile Device __________________ I'm on the Instagram- @Gearhead_Kevin

03-25-2011, 06:33 PM	#9
4x4toy Registered User Join Date: Jan 2009 Location: Southern Md Posts: 228	Re: How to identify what my gear ratio is? Pull the cover, its probably over due for a gear oil change anyway. __________________ 04 Yukon XL 2500 w/ Quadrasteer 61 Chevy C60, 261 inline six 86 Chevy C20 2wd, Banks 6.2 05 GMC Sierra 2500hd Duramax

03-25-2011, 06:35 PM	#10
Leedogg Registered User Join Date: Jan 2010 Location: Brewton AL Posts: 236	Re: How to identify what my gear ratio is? I am going to do the spin the pinion for the tire to spin 1 round first- then if that fails- pop the cover and count teeth. edit...had it backwards..doh...was half asleep. __________________ 1989 Chevy Crew Cab Dually - 454/400, Trans Am Hauler, Future bagged project. 96 Trans Am: 383/m6 - 11.98@115 on 315 M/T D/R's - 408rwhp 394 rwtq 05 VW Passat TDI - 38mpg @75mph 07 Bandit 1250S - Two wheeled fun! Click here to see my FQuick Garage! Last edited by Leedogg; 03-26-2011 at 12:12 AM.

03-26-2011, 10:59 PM	#16
rayfinseats Registered User Join Date: Dec 2010 Location: sioux city, iowa Posts: 619	Re: How to identify what my gear ratio is? Rotating the tire method works fine. As far as accuracy, you've got 2.73, 3.08, 3.42, 3.73 and 4.11 common ratios. It's accurate enough to tell them apart. AGREE. I once had one that came out to 2.5. I thought I was on drugs. Pulled the cover and sure enough it was a 2.56. No wonder it took 1/2 a block to spin the tires.

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