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Unread 09-12-2013, 04:47 PM   #1
joe19934
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Are Front to Rear Differential Ratios the same ?

Ok I found a Rear Differential for $125 only thing is I'm not sure about the ratio as there is no tag on it.
I pulled of and cleaned the front tag & it says 3.73 so should the rear differential be the same ?
Logically I would think it had to be the same ratio does anyone have any feedback or suggestion on this ?
Thank you in advance,

Joe

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Unread 09-12-2013, 04:49 PM   #2
jm8881
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Yes. Unless it's a trail only rig but then they should be within .01. Like 4.11's in (i think) fords and 4.10 in jeeps/chevy.
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Unread 09-12-2013, 05:00 PM   #3
riot1987
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F&R have to be the same ratio or it will bind in 4wd
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Unread 09-12-2013, 05:04 PM   #4
joe19934
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Originally Posted by riot1987 View Post
F&R have to be the same ratio or it will bind in 4wd
That's what I figured because it would mess up the AWD
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Unread 09-12-2013, 05:12 PM   #5
riot1987
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3.73's were very common in ZJ's there were also made with 3.55's so you have to watch for those
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Unread 09-12-2013, 05:32 PM   #6
joe19934
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Originally Posted by riot1987 View Post
3.73's were very common in ZJ's there were also made with 3.55's so you have to watch for those
OK got it but the front tag says 3.73 I hope someone didn't change it...
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Unread 09-12-2013, 05:57 PM   #7
newfieZJ
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Since this is a new to you diff , your gonna want to change the oil . When you pull the cover , on the side of the ring gear will be stamped 41/11 , just rotate till seen . That's a 3.73
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Unread 09-13-2013, 04:21 PM   #8
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Originally Posted by newfieZJ View Post
Since this is a new to you diff , your gonna want to change the oil . When you pull the cover , on the side of the ring gear will be stamped 41/11 , just rotate till seen . That's a 3.73
You can determine the ratio of any setup by finding the numbers on the ring gear that newfieZJ mentioned and dividing the first number by the second number.
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Unread 09-13-2013, 10:32 PM   #9
joe19934
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Ok it took me most of the day but I got home today with a 3.73 Rear for only $125 after looking it over at the parts salvage yard...
I see it as a day spent driving around with the Wife lol
Anyway when I got home I crawled under the Jeep and spotted 1 difference which is I have a vent on the left side and the brake splitter block is on the left side of the rear.
The one I just picked up looks to only have the vent that is routed through the brake splitter block which I hope wont make any difference I hope ??????
Could the one I just picked up be out of a older model mine is a 98 !
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Unread 09-14-2013, 01:09 AM   #10
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Quote:
Originally Posted by joe19934 View Post
Ok I found a Rear Differential for $125 only thing is I'm not sure about the ratio as there is no tag on it.
I pulled of and cleaned the front tag & it says 3.73 so should the rear differential be the same ?
Logically I would think it had to be the same ratio does anyone have any feedback or suggestion on this ?
Thank you in advance,

Joe
Yes, within a couple of points. If they're not close, the tcase will end up binding because it can't spin the shafts differently.

If it's a different ratio, you can remove the associated driveshaft until you can get the axle regeared with no ill effect.
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Unread 09-14-2013, 04:38 AM   #11
joe19934
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Originally Posted by 5-90 View Post

Yes, within a couple of points. If they're not close, the tcase will end up binding because it can't spin the shafts differently.

If it's a different ratio, you can remove the associated driveshaft until you can get the axle regeared with no ill effect.
The one I just picked up has the same 3.73 ratio as the front one IRS just the single vent tube I was worried about on the replacement rear.
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Unread 09-14-2013, 05:25 AM   #12
newfieZJ
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Me thinks you bought a D35 , not a 44a . Bolts up and will work , but , your driveshaft is going to be 1 " short at least now
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Unread 09-14-2013, 08:21 AM   #13
joe19934
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Originally Posted by newfieZJ View Post
Me thinks you bought a D35 , not a 44a . Bolts up and will work , but , your driveshaft is going to be 1 " short at least now
OK if it is beside bringing back what could be done?
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Unread 09-14-2013, 08:29 AM   #14
newfieZJ
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If you want no hassle with the drive shaft , return it , get a 44a . Diff has an aluminum case on the 44a , bring a magnet .
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Unread 09-14-2013, 09:28 AM   #15
joe19934
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Originally Posted by newfieZJ View Post
If you want no hassle with the drive shaft , return it , get a 44a . Diff has an aluminum case on the 44a , bring a magnet .
OK just checked it and a magnet sticks to it so I'm guessing you're right its a Dana35...
I just called the Owner of the Parts Yard and it was taken out of a 1998 Grand Cherokee with a 5.2L so I'm guessing the owner of the Jeep swapped it out and the person I bought it from has no Idea what he's selling ????????
Can my driveshaft be modified or will it work as is for now ?
What if the guy has the rear driveshaft that came out of that Jeep maybe that has been modified to work already ?

Last edited by joe19934; 09-14-2013 at 10:24 AM.. Reason: spelling
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