Jacked Up rear diff
JK Super Freak
Joined: Jun 2011
Posts: 1,206
Likes: 0
From: Elizabethtown, PA
Originally Posted by BBD08Unlimited
So just got my jk a couple weeks ago. Put it up on a lift to see what kind of conditions its in and come to find previous owner never changed any fluids other than oil. So spent the day changing all the fluids. pulled the rear diff cover to find first i have a 3.21 gear ratio. And some idiot has taken apart the rear diff and put it back together wrong. Sorry don't remember names of the components. I'm a generator mechanic so still learning how to work on everything past the engine. But had a mechanic look at it while i had the cover off. If you look at the left side where the clamp is holding the axle and the bearing in you'll notice the gap is all jacked up but its pointless to fix unless i buy a rebuild kit. and its pointless to buy a rebuild kit since i am going to regear it anyway. Atleast the backlash wasn't bad. So hopefully it doesn't actually break before i can afford new gears. but if anyone would like to donate a bigger gear set. I won't complain.
<img src="https://www.jk-forum.com/forums/attachment.php?attachmentid=263142"/><img src="https://www.jk-forum.com/forums/attachment.php?attachmentid=263143"/>
Atleast it looks like the last owner never offroaded it at all so all damage to the bottom that comes will be from me.
Oh and whoevers idea it was to run the exhaust 2 inches below the tranny drain plug is an A$$hole. Had to cut an 17mm allen key and weld it to a 17 mm box wrench to get the drain plug out. They do that crap just so you take it to them for services.
<img src="https://www.jk-forum.com/forums/attachment.php?attachmentid=263142"/><img src="https://www.jk-forum.com/forums/attachment.php?attachmentid=263143"/>
Atleast it looks like the last owner never offroaded it at all so all damage to the bottom that comes will be from me.
Oh and whoevers idea it was to run the exhaust 2 inches below the tranny drain plug is an A$$hole. Had to cut an 17mm allen key and weld it to a 17 mm box wrench to get the drain plug out. They do that crap just so you take it to them for services.
JK Super Freak
Joined: Jun 2011
Posts: 1,206
Likes: 0
From: Elizabethtown, PA
What year is your JK? And does it have a tow package? I was told when I bought my '08 that with tow package it has 3.73 gears but I don't know how to verify this. My build sheet says 3.21 under the standard options. But I guess the tow package is in the preferred packages?
Thread Starter
JK Newbie
Joined: Dec 2011
Posts: 54
Likes: 0
From: colorado springs co
Sorry had to leave the tool at the autoshop but its pretty easy to explain take a 17 mm allen key cut 1 -1.25 off the long end. insert into the box end of a 17mm wrench. and weld it all together. i took my tranny plug out before i welded it just taped it in so it didn't fall out the bottom as i tried to get it into that tight little spot. hope that helps when i go back i'll try to remember to take a photo.
i have an 08unlimited hence my nick. but i don't have a tow package and it comes with the 3.21 stock.
What year is your JK? And does it have a tow package? I was told when I bought my '08 that with tow package it has 3.73 gears but I don't know how to verify this. My build sheet says 3.21 under the standard options. But I guess the tow package is in the preferred packages?
Thread Starter
JK Newbie
Joined: Dec 2011
Posts: 54
Likes: 0
From: colorado springs co
if you pull off your diff cover. look at the big gear thats edge is towards you. on it you will see 2 numbers. on a 3.21 its 45/14. take the large number and divide it by the small number and that gives you your gear ratio. so 45 divided by 14 equals 3.21 other than taking off the diff cover i don't know of any other way. make sure you have a can of non chlorinated brake cleaner to clean everything out so you can check the condition of everything while you have it open. some high oil resistant silicone rtv. and some new royal purple 75/90 oil to fill the diff back up when you are done.
JK Jedi Master
Joined: Feb 2008
Posts: 12,907
Likes: 185
From: Maine
What year is your JK? And does it have a tow package? I was told when I bought my '08 that with tow package it has 3.73 gears but I don't know how to verify this. My build sheet says 3.21 under the standard options. But I guess the tow package is in the preferred packages?
Chock the front tires, fore and aft.
Put the transmission in neutral.
Emergency brake off.
Jack the left rear tire off the ground.
Put a jack stand under the frame, just in case the jack fails (had to add this).
Put an index mark on the aft end of the drive shaft, visible from the left rear wheel.
Put an index mark on the left rear tire at the 6 o'clock position.
Rotate the left rear tire 2 complete revolutions while counting how many times the index mark on the drive shaft passes its original position.
That number will be your axle ratio.
Remove jack stand and lower jack.
Put transmission in gear or Park, apply emergency brake.
Remove chocks.
If you have limited slip, jack up both rear wheels and rotate one revolution, making sure both tires rotate equally.
If the drive shaft rotated almost 3¼ turns, you have 3.21
If the drive shaft rotated almost 3¾ turns, you have 3.73
If the drive shaft rotated a little over 4 turns, you have 4.10
If the drive shaft rotated 4½ turns, you have 4.56
If the drive shaft rotated a little under 5 turns, you have 4.88
If the drive shaft rotated a little over 5 turns, you have 5.13
JK Jedi Master
Joined: Feb 2008
Posts: 12,907
Likes: 185
From: Maine
For some strange reason, people prefer getting their Jeep's gear ratio information through the keyboard, rather than actually getting their hands on the Jeep.
It's nice to have a build sheet, but it may not reflect what's in the Jeep, especially if it was purchased used.
Thread Starter
JK Newbie
Joined: Dec 2011
Posts: 54
Likes: 0
From: colorado springs co
I love getting under my vehicles. Its the best way to learn your vehicle so u know how to quick fix when something does go wrong. Tightening the ebrake and rotating tires this weekend. And possibly swapping up to some rubicon tow springs. Get an extra inch out of em hopefully. If not stiffer suspension is always nice.
Edit to avoid double post: If i pick up a set of used gears from the sale forum. what else will i need to install other than tools. Do i need to get a rebuild kit? planning on upping to 4.10's. also if someone knows where the link to identify the type of diff you have I would appreciate it. saw it once but didn't print or bookmark. and now i need it and can't find the blasted thing. thanks
Edit to avoid double post: If i pick up a set of used gears from the sale forum. what else will i need to install other than tools. Do i need to get a rebuild kit? planning on upping to 4.10's. also if someone knows where the link to identify the type of diff you have I would appreciate it. saw it once but didn't print or bookmark. and now i need it and can't find the blasted thing. thanks
Last edited by BBD08Unlimited; Jan 13, 2012 at 10:41 AM.
JK Enthusiast
Joined: Aug 2011
Posts: 436
Likes: 0
From: Lima, ny
Doing the gears is a tall order, I would make sure you know what you're getting into before you dive in! that said, I know nothing on replacing gears and what is involved just repeating the warnings I've heard! Here's your pic!