Checking My Gear Ratio..What Am I Doing Wrong? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

magwakeenercew2jh · 07-04-2012, 07:25 PM

One full revolution of the rear wheel (in neutral): One and a half full revs of the drive shaft.

Hummmm? Blocked the passenger's side rear wheel from rotation. Same count.

I was on the wheel checking the wheel's t.d.c. on each attempt, and a partner was under the truck counting the d.s. revs.

Same result on all tries. Am I dumb? Can't he count? Am I working on a Corvair Monza?

gcburdic · 07-04-2012, 07:33 PM

try 2 rotations

sounds like a 3.07 gear

Mike C · 07-05-2012, 07:17 PM

When you have an open diff and rotate just one tire, the spider and side gears reduce the number of driveshaft revolutions by half, so you must do two rotations in this scenario as mentioned above. With a limited slip and both off the ground, only need one rotation to get it.

Hard Luck · 07-09-2012, 11:44 PM

Rotate the Driveshaft 2 times and count the wheel revs then divide by two

Frijolito1988 · 07-10-2012, 01:07 AM

You have to rotate the tire twice., if you are getting 1 1 /2 driveshaft turns at 1 tire turn, then you more than likely have 3.07. If you were to rotate twice you will get a tad over 3 rotations.

These are guestimates , for a chevy rear end when you turn the wheel twice, non posi. I think if you have a posi you only have to rotate once.

a tad over 4 driveshaft rotations +/- = 4.11

3 3/4 driveshaft rotations +/- = 3.73

3 1/2 driveshaft rotations +/- = 3.43 ?

3 driveshaft rotations =/- = 3.07.

magwakeenercew2jh · 07-10-2012, 01:12 AM

Since I rotated the wheel once and got 1.5 revs of the driveshaft, I have to figure 2 rotations of the wheel would give me 3 rotations of the driveshaft.

So, my fundamental brain says. 3.0:1.0.

Which, giving a margin for error based on eyeballing, seems to easily translate to 3.07.

Does that make sense?

l l l l
AHHHH, YES!!!! Thanks, All. V V V V

**jocko** · 07-10-2012, 01:27 AM

yep, you got it!

07-04-2012, 07:25 PM	#1
magwakeenercew2jh RAT1968 '68 Cab/'71 Parts Join Date: Feb 2002 Location: Coarsegold, CA Posts: 2,375	Checking My Gear Ratio..What Am I Doing Wrong? One full revolution of the rear wheel (in neutral): One and a half full revs of the drive shaft. Hummmm? Blocked the passenger's side rear wheel from rotation. Same count. I was on the wheel checking the wheel's t.d.c. on each attempt, and a partner was under the truck counting the d.s. revs. Same result on all tries. Am I dumb? Can't he count? Am I working on a Corvair Monza? Attached Images __________________ M17 Coarsegold, CA RAT's shiny now. But always a rat.

07-04-2012, 07:33 PM	#2
gcburdic Restoration Virgin! Join Date: Jan 2008 Location: Huntersville, NC Posts: 8,298	Re: Checking My Gear Ratio..What Am I Doing Wrong? try 2 rotations sounds like a 3.07 gear __________________ Geoff with a G 1968 Chevy C10 SWB The Mistress 1972 Custom Deluxe C20 Suburban A Suburban Named Isabella 1966 Ford Mustang Mama's High School Graduation Present

07-05-2012, 07:17 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,723	Re: Checking My Gear Ratio..What Am I Doing Wrong? When you have an open diff and rotate just one tire, the spider and side gears reduce the number of driveshaft revolutions by half, so you must do two rotations in this scenario as mentioned above. With a limited slip and both off the ground, only need one rotation to get it. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

07-09-2012, 11:44 PM	#4
Hard Luck I've got grease on my mind. Join Date: Sep 2007 Location: Oly, Wa Posts: 481	Re: Checking My Gear Ratio..What Am I Doing Wrong? Rotate the Driveshaft 2 times and count the wheel revs then divide by two

07-10-2012, 01:07 AM	#5
Frijolito1988 Registered User Join Date: Jul 2010 Location: So Cal Posts: 421	Re: Checking My Gear Ratio..What Am I Doing Wrong? You have to rotate the tire twice., if you are getting 1 1 /2 driveshaft turns at 1 tire turn, then you more than likely have 3.07. If you were to rotate twice you will get a tad over 3 rotations. These are guestimates , for a chevy rear end when you turn the wheel twice, non posi. I think if you have a posi you only have to rotate once. a tad over 4 driveshaft rotations +/- = 4.11 3 3/4 driveshaft rotations +/- = 3.73 3 1/2 driveshaft rotations +/- = 3.43 ? 3 driveshaft rotations =/- = 3.07. Last edited by Frijolito1988; 07-10-2012 at 01:13 AM.

07-10-2012, 01:12 AM	#6
magwakeenercew2jh RAT1968 '68 Cab/'71 Parts Join Date: Feb 2002 Location: Coarsegold, CA Posts: 2,375	Re: Checking My Gear Ratio..What Am I Doing Wrong? Since I rotated the wheel once and got 1.5 revs of the driveshaft, I have to figure 2 rotations of the wheel would give me 3 rotations of the driveshaft. So, my fundamental brain says. 3.0:1.0. Which, giving a margin for error based on eyeballing, seems to easily translate to 3.07. Does that make sense? l l l l AHHHH, YES!!!! Thanks, All. V V V V __________________ M17 Coarsegold, CA RAT's shiny now. But always a rat.

07-10-2012, 01:27 AM	#7
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,976	Re: Checking My Gear Ratio..What Am I Doing Wrong? yep, you got it!



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