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07-24-2007, 05:00 PM
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#1 |
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Registered User
Join Date: Jul 2007
Location: Mendenhall MS
Posts: 222
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What Gear Ratio
I know I could pull the diff cover and count the teeth on the ring gear and the pinion gear to determine gear ratio, but I'm being a bit lazy. Was there a typical gear ratio on the '72 GMC? Maybe a couple possibilities I might could narrow it down too? I'd say I'm geared pretty low but that's about all I could say. @ highway speeds I'm revving pretty good, and it feels pretty torquey at take off.
Best guesses? |
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07-24-2007, 05:05 PM
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#2 |
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Senior Member
 
Join Date: Mar 2005
Location: weatherford,texas
Posts: 1,003
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Re: What Gear Ratio
3.73's
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07-24-2007, 05:39 PM
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#3 |
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member #16
 
Join Date: Dec 1999
Location: Yuba City Ca.
Posts: 3,618
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Re: What Gear Ratio
Which engine & trans? 1/2 ton or 3/4 ton?
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john http://67-72chevytrucks.com/vboard/showgroups.php board vendors  http://www.flickr.com/photos/1745471...7602865984234/ |
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07-24-2007, 06:44 PM
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#4 |
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Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: What Gear Ratio
Try this: http://www.442.com/oldsfaq/ofdif.htm
If you just want a pretty close ball park figure and don't want to do a tear down. I used white chalk mark on the inside of the tire and a wire stuck in the ground to point to it where I can see it as I rotated the axle. Also chalk marked the axle and the rear end so I could count the revolutions.... |
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07-24-2007, 07:07 PM
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#5 |
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Registered User
Join Date: Dec 2006
Location: Rhode Island
Posts: 602
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Re: What Gear Ratio
Yeah. I agree.
If all you want is a rough guestimate, I'd just roll the truck forward in a straight line one complete rear tire revolution and count the number of complete and fractional driveshaft revolutions. That'll get you within 5% I'll bet. (Safety 1st though. Don't do this while under the truck and on a hill)
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69 C-10 SWB Fleetside 454/TH400 (For Sale) http://67-72chevytrucks.com/vboard/c...ct=1299&cat=12 70 El Camino 454 TH700 29 Model A 4-DR Sedan Deluxe Last edited by mnunn454; 07-24-2007 at 07:09 PM. |
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07-24-2007, 07:16 PM
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#6 |
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Senior Member
Join Date: Jul 2004
Location: Estherville, Iowa
Posts: 3,371
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Re: What Gear Ratio
Surefire way to tell - assuming you do not have posi - this takes some patience and a helper. Tranny must be in neutral, thennjack on rear wheel up, block front wheels so you don't hurt yourself. Put a chalk mark on the driveshaft. Turn rear wheel exactly 20 times, if drive shaft turns 41 times you have a 4.10, 37 1/3 times a 3.73, almost 31 times would be a 3.07. etc.
If you have posi, then just turn the wheels 10 times.
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1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0 |
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07-24-2007, 07:22 PM
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#7 |
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its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: What Gear Ratio
surefire way?
Pop the cover off, count the teeth, and replace the oil that is at least 10 years old... possibly 35 years old. 
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07-24-2007, 07:32 PM
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#8 |
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Senior Member
Join Date: Jul 2004
Location: Estherville, Iowa
Posts: 3,371
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Re: What Gear Ratio
Longhorn is right, best to get that old nasty stuff out of there, but if you just want to find out the ratio and not get dirty right now just spin the tires.
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1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0 |
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07-24-2007, 10:13 PM
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#9 |
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Registered User
Join Date: Jun 2002
Location: Knoxville Tenn.
Posts: 3,058
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Re: What Gear Ratio
Or if open rear turn tire 1 time and X by 2 the driveshaft turns.
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56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer |
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