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Unread 03-03-2013, 08:23 PM   #1
icemann0014
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1997 TJ Wrangler 
 
Join Date: Jul 2011
Location: WATERFORD, VIRGINIA
Posts: 55
Gear Ratio Question

I have a few stupid beginner questions about axles, gear ratios and such.
i have a 97 sport with a d35 in the rear and a 30 in the front with the ax15 transmission.



according to the stock tj spec page, the standard gear ratio for 6 cylinder models is 3.07.

stock gear ratio options available with the d35 are 3.07, 3.55, 3.73, 4.11, 4.56.

the ax15 tranny has 1st - 3.83 2nd - 2.33 3rd - 1.44 4th - 1.00 5th - 0.79 Rev - 4.22.



so basically my stuped question is what do all of these numbers mean?

why is the gear ratio 3.07 while no gear in the transmission is that ratio?

when you upgrade you gears, do you upgrade your front and rear axles, as well as your trans?

how can i find out what my gear ratio is to be positive? im like 99% sure i have a d35 because it has the rubber fluid hole



thank you so much for helping out and im sure ill think of more questions later

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Unread 03-03-2013, 08:32 PM   #2
idskot
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1991 YJ Wrangler 
 
Join Date: Dec 2011
Location: Miami, Florida
Posts: 814
Quote:
Originally Posted by icemann0014 View Post
I have a few stupid beginner questions about axles, gear ratios and such.
i have a 97 sport with a d35 in the rear and a 30 in the front with the ax15 transmission.



according to the stock tj spec page, the standard gear ratio for 6 cylinder models is 3.07.

stock gear ratio options available with the d35 are 3.07, 3.55, 3.73, 4.11, 4.56.

the ax15 tranny has 1st - 3.83 2nd - 2.33 3rd - 1.44 4th - 1.00 5th - 0.79 Rev - 4.22.



so basically my stuped question is what do all of these numbers mean?

why is the gear ratio 3.07 while no gear in the transmission is that ratio?

when you upgrade you gears, do you upgrade your front and rear axles, as well as your trans?

how can i find out what my gear ratio is to be positive? im like 99% sure i have a d35 because it has the rubber fluid hole



thank you so much for helping out and im sure ill think of more questions later
You're in the wrong section, but the question still applies...

When people talk about 3.07, 3.55, etc... they're talking about the axle's gear ratio.

That is, the number of teeth on the pinion in relation to the number of teeth on the ring. This ends up being the 'final gear'. When people change gears, they change the gear ratio for the front and rear. They don't change the actual gears inside of the transmission. Both gear ratios in each axle have to be the same, or problems will arise. I assure you.

As for the numbers, there's two ways of checking... each engine / transmission has a set gear ratio. I.E. Inline-4 manuals all have 4.11 gear ratios, stock.

Another way is to physically check. Jack up a wheel on each axle, and spin it with a piece of yarn or thread taped in the middle. After two complete rotations, you will have your gear ratio when you count the turns on the yarn/thread.
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Unread 03-03-2013, 08:37 PM   #3
Mark05059
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1989 YJ Wrangler 
 
Join Date: Mar 2009
Location: quechee Vermont
Posts: 4,332
the gear ratio's in the transmission have nothing to do with the gear ratios in the axles.

Ill try to explain. if you have 2 gears with 10 teeth each it would be 1:1 gear ratio and would have no advantage/disadvantages at all. the gears in the rear/front are 3.07/1 meaning the driveshaft/pinion will turn a little over 3 turns to make the ring turn once. Basically the same for the transmission. When changing gear ratios its seldom done by changing transmission gears and generally done at the rear axle. If you have more questions or want more clarification on things just ask..
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Unread 03-03-2013, 08:56 PM   #4
StayClassy
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2006 TJ Wrangler 
 
Join Date: May 2012
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Or a lazy way to find out your gear ratio is to request a build sheet from Jeep. Just give them your VIN.

But the yarn method would be more fun.
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Unread 03-03-2013, 09:02 PM   #5
idskot
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1991 YJ Wrangler 
 
Join Date: Dec 2011
Location: Miami, Florida
Posts: 814
Quote:
Originally Posted by StayClassy View Post
Or a lazy way to find out your gear ratio is to request a build sheet from Jeep. Just give them your VIN.

But the yarn method would be more fun.
If not less exciting!
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Unread 03-04-2013, 06:54 AM   #6
Cherokid
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1989 YJ Wrangler 
 
Join Date: Apr 2009
Location: Long Beach, CA
Posts: 66
and if you want to see what the different gear ratios will do for your rpm (engine speed) at any given road speed go to grimmjeepers gear ratio page, fill in the fields with the info about your jeep and hit 'calculate'.

Good Wheelin to ya,

Cherokid
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Unread 03-04-2013, 03:02 PM   #7
icemann0014
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1997 TJ Wrangler 
 
Join Date: Jul 2011
Location: WATERFORD, VIRGINIA
Posts: 55
great thank you all so much. that really cleared all of that up for me. as soon as i get my baby back from the shop, i will know for sure
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