Checking Gear Ratios
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Posting Guru
Joined: Dec 2006
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From: N. Fort Myers,FL
Checking Gear Ratios
From what i heard from friends, is that to check your gear ratio in your rear end, you mark on your tire and spin it 1 revolution, and count how many times the pinion spins. Ex- 3.55 pinion revolutions to 1 tire revolution, is a 3.55 gear ratio?
Post Fiend
Joined: Jul 2006
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Trying to see a difference between 3 3/4 revolution and 3 1/2 is tough to do.
The absolute best verification is to remove the inspection cover and count the teeth.
The inspection cover is called this so we can inspect the differential. Odd how so many people never remove it for nromal maintenance or inspection.
Take the thing off and get a good look at the gears and inspect the fluid for metal. This will save you a bunch of trouble later down the road. At that time you can count the teeth on the gears and do a little grade school math and know the exact gear ratio, and the condition of the components.
The absolute best verification is to remove the inspection cover and count the teeth.
The inspection cover is called this so we can inspect the differential. Odd how so many people never remove it for nromal maintenance or inspection.
Take the thing off and get a good look at the gears and inspect the fluid for metal. This will save you a bunch of trouble later down the road. At that time you can count the teeth on the gears and do a little grade school math and know the exact gear ratio, and the condition of the components.
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Posting Guru
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From: N. Fort Myers,FL
well i know you can do those things, but this is an old 1980 jeep.
Does that method i explained work? i tried it today and by that method it said that it was like a 1.60 gear ratio which isnt right(the guy i bought it from said that it has 3.54 gears). I will be doing fluid changes before i start driving it so i can check the ring and pinion condition then but i just want to know if that method works.
I keep thinking that when i checked my truck it came out 3.5 turns(which only ratio close is a 3.55) and i also checked to see what the door told me and it told me it was a 3.55LS. Any thoughts?
Does that method i explained work? i tried it today and by that method it said that it was like a 1.60 gear ratio which isnt right(the guy i bought it from said that it has 3.54 gears). I will be doing fluid changes before i start driving it so i can check the ring and pinion condition then but i just want to know if that method works.
I keep thinking that when i checked my truck it came out 3.5 turns(which only ratio close is a 3.55) and i also checked to see what the door told me and it told me it was a 3.55LS. Any thoughts?
Hotshot
Joined: Oct 2002
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From: The Big, Oregon
You have to have both tires off the ground or the count will be off. Both tires also have to spin. On the Dana axles, once you pull the diff cover, spin the ring around and look for some stamped numbers on the edge. That's your gear ratio there.
Posting Legend
Joined: Sep 2001
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From the 73-9 forum FAQ:
Differential Gear Ratio Determination
This method was contributed by member: theonlybull
What I do, is jack one tire up, mark it, then mark the driveshaft. Now one person turns the one rear tire 20 times, and the other person counts the driveshaft rotations. Then divide the resulting turns of the driveshaft by 10. If you count 35, then you have 3.50 gears..
Doing it this way will let you tell the difference between 3.00, and 3.10 gears.
This method was contributed by member: theonlybull
What I do, is jack one tire up, mark it, then mark the driveshaft. Now one person turns the one rear tire 20 times, and the other person counts the driveshaft rotations. Then divide the resulting turns of the driveshaft by 10. If you count 35, then you have 3.50 gears..
Doing it this way will let you tell the difference between 3.00, and 3.10 gears.
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Posting Guru
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From: N. Fort Myers,FL
when i checked it today i chocked 1 tire(1 wheel peel) and spin the other and came up with a 1.6 ratio. Is it because i chocked the other tire that the number came out wierd?
A 4.10 ratio means that the pinion spins 4.1 times to one tire rotation correct? If so why would you spin the tire 20 times then divide, wouldnt be easier to only do it once? Yeah it might be more precise to do it alot but its basically the same thing, right?
A 4.10 ratio means that the pinion spins 4.1 times to one tire rotation correct? If so why would you spin the tire 20 times then divide, wouldnt be easier to only do it once? Yeah it might be more precise to do it alot but its basically the same thing, right?
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