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Old 06-18-2013, 05:11 PM   #1
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Gearing Explanation ???

A lot of people on our forum talk about changing out the rear end of their Jeep.

Can someone explain the difference between a 4.10 and a 4.88 (I think I got that right), as well as other rear ends?


I know that it has to do with how many revolutions the drive shaft turns, compared to the tires. But, other than that, I'm lost.
  • How do you know which rear end you need to change out to?
  • Are all of the TJ rear ends interchangeable? Or, only certain years?
  • Does the size of the tire determine which rear end you need to go with?
I saw where someone on our forum posted pictures, illustrating what the Dana 30, 35, 44, etc. look like, but are they interchangeable?

From what I have read, it seems like the Dana 44 is the best.
Or is there a better one than the Dana 44?

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Old 06-18-2013, 05:49 PM   #2
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Tell us about your rig so we can better assist you

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Old 06-18-2013, 06:41 PM   #3
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I don't have one yet.

I just want to understand the differences.
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Old 06-18-2013, 06:48 PM   #4
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Dana 30->35->44->60, etc. denotes increase in strength required for the application.
Higher gearing, 4.11 vs 4.88; 4.88 being higher, denotes greater mechanical advantage over output at the wheels for any given gear of the tranny.

More or less, the stronger the axle you're running, the better it'll support a larger tire size. The 44's on the tj's being acceptable to around 35's, the JK ones/newer gen axles around 37's, and 60's for 40, 42. The harder you drive, the stronger axle you may need regardless.

As tire size increases, you'll want larger gears.
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Old 06-18-2013, 06:52 PM   #5
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Nothing significant between Dana 30, Dana 35, or Dana 44 axles is interchangeable. They are all different sizes for strength reasons.

Axle ratios have to do with how fast your engine spins at a certain speed. A 4.88 is a "lower" ratio than 4.56 & an engine with 4.88 gears in its axles will spin faster at a given speed than if if the axles had 4.56 gears inside.

That is why we upgrade our axles from factory 3.07, 3.73, etc. ratios to lower ratios like 4.10, 4.56, or 4.88. To increase engine RPMs so the engine can more easily turn bigger tires which is the usual reason for installing lower axle gear ratios like 4.56 or 4.88.

Yes I know 4.88 is a higher number than 4.10 but in ratio-speak, 4.88 for example is a lower ratio than 4.10. 3.73 is a lower ratio than 3.07 is. 3.73 is higher numerically than 3.07 is, yes, but in ratio-speak, 3.73 is a lower ratio than 3.07 is.

An axle with 4.88 gearing inside will turn the tire 1 time for every 4.88 turns of the driveshaft that drives the axle. So the driveshaft spins faster with 4.88 gears than it would with 3.73 gears so the engine runs at a higher rpm which produces more hp. Which is why we regear, because it takes more hp to turn bigger tires.

The driveshaft is connected to the pinion shaft, and the pinion shaft turns the ring gear which is connected to the axle shafts and thus the wheels.

The big gear in the below photo is the ring gear which is connected to the axle shafts. The smaller gear is the pinion gear which connects the axle to the driveshaft.

The small pinion gear on the right is what drives the larger ring gear, and the arrow is pointing towards the front of the vehicle



In terms of axle terminology, the bigger the number, the bigger (stronger) the axle. A Dana 60 is bigger than a Dana 44 which is bigger than a Dana 35, and so on.

Hope this helps.
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Old 06-18-2013, 07:55 PM   #6
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Gear ratios are considered your final drive ratio, as said the lower the gearing (numerically higher) gives you more revolutions of the driveshaft compared to the tires. This is also a torque multiplier, in 4wd low the number can be pretty astounding.

Numerically high gear ratios provide better acceleration because you have more torque at the wheels for any given RPM, but lowers your top speed. Numerically low gears are the opposite, raise your top speed but hurts your acceleration.

In the world of off road you want torque.
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Old 06-18-2013, 08:01 PM   #7
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Numerically high gear ratios provide better acceleration because you have more torque at the wheels for any given RPM, but lowers your top speed. Numerically low gears are the opposite, raise your top speed but hurts your acceleration.
It is not necessarily true that a numerically higher axle ratio number (lower ratio) will lower your top speed & visa-versa.

Running too high of a ratio can reduce your top speed which means going to a lower ratio can increase your top speed. For example if you were running 3.07 gearing & increased your tire size to 35", you'd barely be able to maintain a legal speed on the highway. Going to a lower ratio will raise the engine rpms in that case which will increase power & thus the top speed.
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Old 06-18-2013, 08:10 PM   #8
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you'd barely be able to maintain a legal speed on the highway.
Not necessarily true. You could maintain legal speed on the highway, but might have to stay in 4th or 3rd to do so.
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Old 06-18-2013, 08:21 PM   #9
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It is not necessarily true that a numerically higher axle ratio number (lower ratio) will lower your top speed & visa-versa.

Running too high of a ratio can reduce your top speed which means going to a lower ratio can increase your top speed. For example if you were running 3.07 gearing & increased your tire size to 35", you'd barely be able to maintain a legal speed on the highway. Going to a lower ratio will raise the engine rpms in that case which will increase power & thus the top speed.
Of course there are many real world factors to consider, it's just a general rule when speaking of cars across the board. Most vehicles aren't underpowered bricks with large tires driving down the road.
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Old 06-18-2013, 08:25 PM   #10
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Of course there are many real world factors to consider, it's just a general rule when speaking of cars across the board. Most vehicles aren't underpowered bricks with large tires driving down the road.
We're talking Jeeps, not cars here.
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Old 06-19-2013, 07:12 AM   #11
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Is 5.38 good for 37's? Which gears need to be chsngef?
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Old 06-19-2013, 07:12 AM   #12
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How much will the regear cost?
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Old 06-19-2013, 07:13 AM   #13
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WhAt geAr brand is the best?
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Old 06-19-2013, 07:43 AM   #14
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Quote:
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Is 5.38 good for 37's? Which gears need to be chsngef?

Yes. Both, if you want to use 4 wheel drive.


Quote:
Originally Posted by Gily View Post
How much will the regear cost?

A lot.


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WhAt geAr brand is the best?

Whichever brand your installer sells and will stand behind.
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Old 06-19-2013, 08:08 AM   #15
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Also you want the front and rear gear to match, so if you do regear it would have to be both axles. Otherwise you can't use 4wd, the vehicle would be fighting itself
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Old 06-19-2013, 08:13 PM   #16
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Thanks, I just ordered a package fron northridge 4x4 with front and rear yukon gears 5.30 and installation kit, how much do the installation run?
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Old 06-19-2013, 08:15 PM   #17
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Thanks
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Old 06-19-2013, 09:24 PM   #18
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Thanks, I just ordered a package fron northridge 4x4 with front and rear yukon gears 5.30 and installation kit, how much do the installation run?
What engine, transmission, and axles do you have? D30 up front?
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Old 06-23-2013, 07:50 PM   #19
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What engine, transmission, and axles do you have? D30 up front?
3.8L, auto, Dana 44s both Rubicon
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Old 06-23-2013, 07:51 PM   #20
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3.8, Auto, rubicon Dana 44s
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Old 06-23-2013, 07:58 PM   #21
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With your automatic 5.38 will barely be low enough for 37" tires but that ratio would be absolutely perfect for 35" tires. Regearing is probably going to be pretty close to $1300-1500 for all parts & labor. I got my last regearing done for just under $1100 but that was only after some serious negotiating.
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Old 06-23-2013, 10:36 PM   #22
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I bought 5.38 from northridge 4x4 last week and the called me and told me it was better to have 5.12 for 35" and I switched to 5.12, I should get them next thursday.
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Old 06-24-2013, 11:45 AM   #23
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I ran 5.38 s in my JK Rubi with 35s and it was perfect. I recommend you do he same.


Flash
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Old 06-24-2013, 12:07 PM   #24
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I know this thread has a few twists-n-turns (pun not really intended), but one consideration that hasn't been mentioned yet in this thread is the "size of the axle". A d44 with 33", will have more ground clearance than and d60 and 33"s, so many opt to not go with d60's and instead build strong d44's and stick with 33"-36" tires.
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Old 06-24-2013, 12:55 PM   #25
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I bought 5.38 from northridge 4x4 last week and the called me and told me it was better to have 5.12 for 35" and I switched to 5.12, I should get them next thursday.
I wouldn't have changed the ratio, 5.38 would be ideal. Sales reps rarely know what they are talking about when recommending ratios & it is rarer yet for them to know the .69 Overdrive issue the 42RLE has which makes a lower than usual ratio advisable.
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Old 06-24-2013, 01:11 PM   #26
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Thanks for this thread I learned a lot. Jerry is like an Encyclopedia Jeep!
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Old 06-24-2013, 11:03 PM   #27
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Does changing the gearing and tire size effect the RPM reading and shifting points?
I'm geared to 4.56 with 36" tires.
I noticed my speedometer is about 10-15 mph higher than my actual speed.
I also noticed that my upshift light comes on at odd times (sometimes it will come on at 2000 RPM and then go back off as I go higher (doesn't really make sense to me).
JJ
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Old 06-24-2013, 11:07 PM   #28
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Does changing the gearing and tire size effect the RPM reading and shifting points?
I'm geared to 4.56 with 36" tires.
I noticed my speedometer is about 10-15 mph higher than my actual speed.
I also noticed that my upshift light comes on at odd times (sometimes it will come on at 2000 RPM and then go back off as I go higher (doesn't really make sense to me).
JJ
That upshift light is completely useless unless your on flat ground. Don't pay any mind to it.
Even when my jeep was completely stock I couldn't shift at the preset points, and retain any momentum going up a slight incline.
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Old 06-24-2013, 11:37 PM   #29
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That upshift light is completely useless unless your on flat ground. Don't pay any mind to it.
Even when my jeep was completely stock I couldn't shift at the preset points, and retain any momentum going up a slight incline.
A lot of people take the bulb out or just put tape over the idiot light. Its useless...
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Old 06-25-2013, 08:05 AM   #30
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fa310tx,

You need to change the speedo gear in your TC if you're sure your speedometer is off. Search for a chart that tells you the right size speedo gear (teeth count) for your tire size/gear ratio.

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