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finding gear ratios.....

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big_truxx

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/forums/images/graemlins/1zhelp.gif i was trying to figure out some diff's ratios today but as ive never done it before think i did it wrong. i thought you jacked a wheel up till it will spin and rotate the driveshaft till the tire rotated one full time and that was yer ratio. but both my dana 70 and 14 bolt were both about 2:1 lol i dont think thats whats in there. did i do this wrong? /forums/images/graemlins/dunno.gif
 
On the ring gear, there will be some numbers stamped. They are the number of teeth on the ring and pinion. Divide them to get the ratio.

Example of a 3.73 setup:

41 11 will be stamped on the ring.

41 = ring teeth
11 = pinion teeth

41/11 = 3.7272727272727
 
/forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif thanks u rock!! i knew there was a reason those #'s were there just not knowing what they meant. and knew how to divide the #'s but couldnt count the pinion. now im straight. thanks.
 
Or if you don't want to remove the diff cover, make a mark on the driveshaft and have someone slowly drive forward until the tires make one revolution. The number of times the driveshaft rotates would be your ratio.
 
If you only jack up only one side and count the driveshaft rotations, you will need to multiply your count by two. Sounds like you've got 4.11's in there.
 
when i looked at my 3/4 ff rear, the #'s at the end of everything were; 41 7 75 now does that mean that the ratio is really 5.86???
 
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when i looked at my 3/4 ff rear, the #'s at the end of everything were; 41 7 75 now does that mean that the ratio is really 5.86???

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thats what it comes to, to be sure, pull the cover and count teeth, 41 on the ring and 7 on the pinion
 
hmmm i counted 41 on ring but the pinion seemed hard to count if it was possible at all. 5.86 is a fairly low gear /forums/images/graemlins/peace.gif
 
I think there was a post about this a few weeks ago. If I recall correctly the gears were made in July '77 (7 75) and the ring gear has 41 teeth. The pinion count would be the number just before the 41. When you get that just divide 41 by that number and there's your ratio. /forums/images/graemlins/thumb.gif
 
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I think there was a post about this a few weeks ago. If I recall correctly the gears were made in July '77 (7 75) and the ring gear has 41 teeth. The pinion count would be the number just before the 41. When you get that just divide 41 by that number and there's your ratio. /forums/images/graemlins/thumb.gif

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That is correct. /forums/images/graemlins/thumb.gif
 
How to I.D. your gear ratio: Count the number of teeth on your ring gear and divide by the numer of teeth on your pinion gear. The result is your gear ratio

Ring gear: 43 teeth.....Pinion 14 teeth....

43 divided by 14 equals 3.07 /forums/images/graemlins/usaflag.gif
 
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hmmm i counted 41 on ring but the pinion seemed hard to count if it was possible at all. 5.86 is a fairly low gear /forums/images/graemlins/peace.gif

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5.86 is not a fairly low gear. Its a REALLY low gear. GM did not put this ratio in any of their axles (except maybe military or extremely heavy duty applications /forums/images/graemlins/dunno.gif) I believe the lowest factory GM ratio is 4.56 and was found in 1 ton military 14 bolts that came from the factory with a detroit locker. I know this because I happen to have one sitting under my K5. Give us the complete line of numbers stamped on your ring gear, and we can figure out your ratio.
-Harrison
 
these are the #'s on the ring;

GM 3992484 1' 41 7 75

i also counted 41 teeth on the ring. but was unable to count the pinion teeth.
 
There shouldn't be an apostrophe in that string of numbers, so it is most likely a 1, and not an apostrophe. So you have 3.73 gears.
 
thats what i was kinda thinkin. the 2nd 1 didnt stamp correctly. i also saw on the pinion a 41 and an 11 this morning when i went to look at the ' again. thanks all for your help educating me on gear ratios!!!! /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif
 
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Yep, 3.73's. Now that you know what the ratio is, time to get LOWER gears. /forums/images/graemlins/thumb.gif
-Harrison

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5.13s /forums/images/graemlins/deal.gif
 
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