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#1 |
Registered User
Join Date: Feb 2011
Location: Brownwood, Texas
Posts: 421
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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
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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 |
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#2 |
Registered User
Join Date: May 2009
Location: Motor City
Posts: 9,194
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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
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#3 |
Active Member
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Location: Marysville, OH
Posts: 667
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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
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#4 |
Registered User
Join Date: Feb 2011
Location: Brownwood, Texas
Posts: 421
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Re: How to identify what my gear ratio is?
Thanks guys
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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 |
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#5 |
Registered User
Join Date: May 2008
Location: Salt Lake City
Posts: 365
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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 |
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#6 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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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.
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#7 |
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Join Date: May 2008
Location: Salt Lake City
Posts: 365
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Re: How to identify what my gear ratio is?
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#8 |
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Join Date: Sep 2009
Location: High Plains of Colorado
Posts: 2,485
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Re: How to identify what my gear ratio is?
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. Last edited by lakeroadster; 03-25-2011 at 07:12 PM. |
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#9 |
Registered User
Join Date: Jan 2009
Location: Southern Md
Posts: 228
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Re: How to identify what my gear ratio is?
Pull the cover, its probably over due for a gear oil change anyway.
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#10 |
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Join Date: Jan 2010
Location: Brewton AL
Posts: 236
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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.
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#11 | |
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Join Date: May 2008
Location: Salt Lake City
Posts: 365
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Re: How to identify what my gear ratio is?
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#12 |
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Re: How to identify what my gear ratio is?
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#13 |
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Re: How to identify what my gear ratio is?
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#14 |
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Re: How to identify what my gear ratio is?
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#15 |
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Re: How to identify what my gear ratio is?
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#16 |
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Join Date: Dec 2010
Location: sioux city, iowa
Posts: 619
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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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