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Unread 06-02-2007, 01:19 AM   #1
keecho
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different gear ratio front and rear

hey fellas
I just figured out that I have diffrent gear ratios in front and rear diff's. How can I tell whats in what? I have a 2004 tj with i6 and 5spd. its a jeep I just purchased last week but it wasnt in driving condition then so I could not test the 4wd.
any id tags or sn #'s I can look at to tell whats in what. I believe I have a 2002 front diff and the rear is the stock 2004. please help
Jack

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Unread 06-02-2007, 01:29 AM   #2
dougolupski
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Well I wouldn't trust the tags on the diff cover the gears can be changed and the tags left on. Your two best bets would be pull the covers off and check the number ratio stamped on the gear. While it works most of the time on factory gears they sometimes don't have a ratio on it just a part number. The other option would be to put you transfer case in neutral and one at a time lift the front and rear. Once you have one up in the air rotate a tire around one full rotation and count the number of times the drive shaft spins. It's best to mark your wheel and driveshaft with something. Example if I rotate my tire around and my driveshaft spins four and a half times I have 4.55 gears. It gets a real good guess of what you have.

What part of Cali are you in?
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Unread 06-02-2007, 01:50 AM   #3
keecho
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thanks for explaning it to me I will jack it up tommorow mornin.
Im in Pasadena CA

Jack
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Unread 06-02-2007, 10:24 AM   #4
Jerry Bransford
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What leads you to believe it has a different f/r axle ratio? A .01 difference in f/r axle ratios is normal except for the Rubicon only because it has matched D44 f/r axles.
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Unread 06-02-2007, 10:52 AM   #5
keecho
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Thanks for your help guys
I did find tags on the diff's
the back for sure is 3-07
and from what I can make out the front is a 4-10? front looks like an older diff housing because the tag was rusted out and the front axle just looks older vs the rear axle .

anyway if I go 33's Im guessing keep the 4-10's? and swap out the back?

Jack
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Unread 06-02-2007, 10:57 AM   #6
Jerry Bransford
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Ok, just verify that they truly are different ratios before doing anything else. You can set the axles on jack stands and after shifting the t-case into neutral, rotate a tire on each axle and carefully note the number of driveshaft revolutions. If they're the same or within a tenth of a rotating the same, you're golden.
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Unread 06-02-2007, 11:02 AM   #7
keecho
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what kind of axle comes with my jeep? do I have a dana 35 in the back and dana 30 in the front? what is suppose to be there?

Jack
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Unread 06-02-2007, 11:05 AM   #8
Jerry Bransford
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Definitely a Dana 30 up front and likely a Dana 35c in back, though it's possible it has the optional better/stronger Dana 44 in the rear.

If the rear axle has an oval-shaped differential cover with a black plastic lubricant hole plug, it's a Dana 35c. If the cover is more stopsign-shaped with a steel bolt in the lube fill hole, it's a Dana 44.
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Unread 06-02-2007, 11:11 AM   #9
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They come with a D35 or D44 in the rear and a D30 in the front.
A 4.10 front D30 would have come out of a 4-banger manual tranny Jeep.
Yes - if the front is 4.10 and the rear is 3.07 do something with the rear.
You may want to upgrade the rear at the same time. Take note that Rubicons have 4.11 gears so maybe just look for a Rubi rear axle which would be a D44 [ much stronger than the 35] and would also have an air locker.
The D35 is not worth putting money into if you plan on 4-wheeling. The other option for it would be a Super 35 kit and regear to 4.11.
As said make sure you have the mismatch before you do anything.
Jim
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Unread 06-02-2007, 11:55 AM   #10
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Quote:
Originally Posted by otisdog
Yes - if the front is 4.10 and the rear is 3.07 do something with the rear.
You may want to upgrade the rear at the same time. Take note that Rubicons have 4.11 gears so maybe just look for a Rubi rear axle which would be a D44 [ much stronger than the 35] and would also have an air locker.
The D35 is not worth putting money into if you plan on 4-wheeling.
As said make sure you have the mismatch before you do anything.
Jim
This sound like a good plan.
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Unread 06-02-2007, 03:03 PM   #11
keecho
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how much money would a dana 44 rear cost if I find one at a jeep junk yard or somthing? what should I be expecting to pay?

Thanks for all the good help
Jack
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Unread 06-02-2007, 05:02 PM   #12
WilliamH
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There's one problem with the suggestion to rotate one tire and count driveshaft revolutions: spider gears.

It should work on a limited slip differential if the clutches are okay (probably limited slip on the rear).

But on an open diff (like the front should be), it woudn't likely work, because the spider gears would most likely turn. I would remove the cover to be sure.
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Unread 06-02-2007, 09:19 PM   #13
dougolupski
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No it works on a open as well, though sometimes you have to put tension on the other wheel to get the DS to rotate. I agree with what everyone said above, it's right on the money. As far as junk yard price for a direct drop in TJ model count on 500.00 or a little more. I bought a TJ d44 housing and it cost me 300 buck just for the used housing alone. The other two options would be to buy an XJ housing than have someone welding on the brackets but it will cost around 400.00 bucks or more to do that. The best way I see from my own experience would be to buy a complete d44 housing with gears and new internals pre made ready to drop in. You can find them at all the major retailers from 1000.00 on up. I know how to do gears but with all the time I spent along with buying all the parts it would have been cheaper in the long run to just buy a complete unit.
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Unread 01-06-2010, 04:32 PM   #14
mrriceguyrj
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I'm going to ask instead of starting a new thread that will discuss the same stuff, does it effect anything to have a different gear ratio in front and rear?

I just recently picked up a '00 2.5L with 32"-33" tires on it, it has stock 4.10 gears installed, but the guy included 4.88 gears for the rear (not installed), and I'm trying to figure out if I should have the rear installed and keep the front at 4.10? This is an every-day driver mainly on streets and 2wd.
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Unread 01-06-2010, 04:35 PM   #15
biffgnar
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Quote:
Originally Posted by mrriceguyrj View Post
does it effect anything to have a different gear ratio in front and rear?
It destroys your transfer case!
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