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Discussion Starter #1
After figuring out it needed major help (what's that grinding-banging noise?), I decided to document my Rear Differential rebuild in the hopes others can learn from my experience. It wasn't very difficult nor required exotic tools, and I suspect most owners with a tad of mechanical experience can easily pull this off. For those more knowledgeable than I at this, please ad advice or corrections as you see fit. It will benefit us all. I used the 2014 Arctic Cat Wildcat/X - Wildcat 4/4X Service Manual for reference.
If you're attempting this, please keep safety in mind and make sure your cat is properly supported when the wheels are off. Besides using a jack and jack stands, I also slid the wheels under the frame... just in case.

To start: Loosten the 30mm axle nuts with the wheels on and grounded, then jack up the cat, safely support it, and remove the wheels. The axle nuts are torqued down pretty good (250ft/lb, cotter pin, and red loctite). I used a big cordless impact wrench, but a 1/2" drive socket wrench with a 2' or 3' piece of pipe as an extention would work just fine. I've read on this Forum that some people heat the axle threads to break down the loctite bond (300 deg?). I didn't need too.

Remove the radius rods from the knuckles (13mm and 17mm wrenches) and support them out of the way. I used a bungee cord to hold them up by the frame.
1 Bungee.jpg
 

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Discussion Starter #2
With the radius rods out of the way you can slip the axle out of the knuckle. Pull the knuckle while pushing the axle. To remove OEM axles from the differential, keep the axle perpendicular to the differential and press the axle shaft towards the differential while pulling back on the inboard axle cup. My OEM axles popped right out. If you're using a Rhino axle, keep the axle perpendicular to the differential and pry lighty (large flathead screwdriver) between the inboard Cup and the Gearcase. I've done this with my new Rhinos and they came out easily.
To access the diffential mounting bolts I had to remove the lower rear radius rods from both sides and the upper rear radius rod from the drivers side.
2 Drivers side radius rods.jpg
3 Pass side radius rods.jpg
 

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Discussion Starter #3
The rear of the Differential is mounted to a Bracket that also holds the lower rear Radius Rods. You need to remove this Bracket.
4 rear bracket.jpg
5 lower rear mount2.jpg
 

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Discussion Starter #4
Remove the upper rear mounting bolt. Note the spacers.
7 upper rear mount.jpg
6 rear upper mount.jpg
 

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Discussion Starter #5
Remove lower front mounting bolt
8 lower front mount.jpg
 

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Discussion Starter #6
The drive shaft is still connected, but will pull free when you slide the Differential back and away from the engine. I had to rotate the Differential about 90 deg (counterclockwise facing forward) and pulled it out rearward and towards the drivers side. It came out easily. Note: There is a Spring inside the engine side of the Driveshaft that will probably pop out. You'll need this Spring later.
9 Diff out rt view.jpg
10 Diff out Lft View.jpg
 

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Discussion Starter #7
I put the Differential in a large plastic container, removed the drain and fill plugs, and drained what used to be the oil. It was now a dark metallic sludge.
Then I removed the front Pinion Housing and got my 1st look at the damage.
1st look at damage.jpg
 

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Discussion Starter #8
Then I removed the side Ring Gear/Case Cover. Damage: The rear Pinion Ball Bearing was destroyed and the Pinion Needle Bearing was completely MIA. The gears themselves looked fine but the nose of the Pinion Gear (where the Needle Bearing rides) was scarred and the Case had some burrs, but not on critical surfaces. I used a Dremmel to clean the case and took the Pinion Gear to a machine shop and had the nose turned down from a scarred 16mm to smooth 15mm. A new Pinion Gear is under $60, and I would have just replaced it, but they are back ordered (2 mos) and I didn't want to wait.
Here's a look at the old Differential parts laid out as removed. Exceptions: I placed the new Pinion Needle bearing in front of the turned Pinion Gear for reference of where it goes. Also there's an installed new bearing on the Case Cover (I didn't want to remove it for the pic).
11 Diff as taken apart.jpg
 

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Discussion Starter #9
I believe the OEM Rear Differential is a little light to handle stock HP and definitely not adequate for modified engines like mine. The OEM Ball Bearings are from a Chinese MFG; PEER (They are marked as PEER with Bearing ID Numbers. I believe the critical Pinion Needle Bearing is a KOYO, which, while Chinese, has a good reputation. Since my Needle Bearing was COMPLETELY destroyed, KOYO is a guess, but I researched for that exact size (16x23x16) bearing and I could only find KOYO 16NQ2316.
All Balls sells a bearing and seal kit (All Balls Bearing/Seal Kit 25-2101) for the big Cat Rear Differential. Even though it's inexpensive (under $60), the Ball Bearings are by KML (China) and I "think" the Pinion Needle Bearing is the same KOYO as OEM. Overall I believe this Kit is as good as OEM and I will use it, with the exception of the critical Needle Bearing. While I couldn't find a replacement Needle Bearing for OEM, I COULD find one with a smaller (15mm) bore. And since I turned down my Pinion Gear nose to 15mm, I can use a high quality SKF Bearing.
12 All Balls RearDiff Kit 25-2101.jpg
 

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Discussion Starter #10
Here's the SKF Needle Bearing next to the All Balls Needle Bearing. Because I turned down the Pinion nose from 16mm to 15mm, I needed a bearing with a smaller (15mm) bore while having the same OD (23mm) and width (16mm).
13 Needle Bearings.jpg
 

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Discussion Starter #11
For those wanting to use better bearings than OEM or All Balls (as I will NEXT time), here is what I would use:
Ring Gear Ball Bearings (2) - OEM 2402-042 is PEER 6008. Use SKF 6008.
Pinion Housing Ball Bearing (1) - OEM 1402-677 is supposed to be a PEER 16008 C3. Mine was stamped Peer 16008, and the All Balls is a KML 16008. No "C3" designation. Use SKF 16008.
Pinion Gear Ball Bearing (1) - OEM 0402-324 is PEER 6007. Use SKF 6007.
Pinion Gear Needle Bearing (1) - OEM 0402-328 is KOYO(?) 16NQ2316. I can't find a better replacement for OEM, but since I tuned my bearing surface down to 15mm, the SKF NK 15/16 is a great replacement bearing.
As for seals, if you're using the All Balls Kit, they're included. If not, Stock seals should be fine. I don't think the seals are a weak link in the Differential.

OK, back to the rebuild. I cleaned everything with Brake Cleaner and did some light deburring of the Case interior with a Sanding Drum on a Dremmel Tool. I used assembly lube when fitting/pressing all bearings and seals. This pic is a REALLY SIMPLE "press" I made to install the Pinion Needle bearing.
14 needle bearing install.jpg
 

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Discussion Starter #12
I used a vice and a PVC fitting that matched the bearing INNER race to press in the Pinion Ball Bearing. If you're using a vice, keep wood between the Pinion Gear and any metal clamping force. This will help protect the Gear.
15 Bearing onto pinion.jpg
 

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Discussion Starter #13
Tap the Pinion Gear assembly into the Gear-case using a PVC fitting that fits the outer race. A Large Circlip secures it. The Circlip has a chamfered side that must face the bearing.
16 pinion assembly.jpg
 

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Discussion Starter #14
I used a PVC fitting to press in the Ring Gear Bearings into the Case and Cover. I heated the bearing seat areas with a Propane Torch to ease installation. With any of the pressed-in bearings like this, one trick is to keep the bearings in the fridge overnight and put the housings into the oven at 200 deg. this is supposed to make installation easier. While I didn't do that, I would next time; it probably reduces any potential for lateral stress when installing.
17 Press Case Bearing.jpg
So now the Pinion is installed and so are the Ring Gear Bearings.
18 gearcase bearings assembled.jpg
 

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Discussion Starter #15
I heated the Pinion Housing to ease getting the front Bearing in and I used another piece of PVC that matched the outer race. There is another chamfered Circlip; install chamfered side towards the bearing.
19 pinion housing parts.jpg
and assembled
20 pinion housing assembly.jpg
 
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Discussion Starter #16
The Ring Gear has one Shim on each side. These shims come in different thicknesses so you can zero in on proper Backlash and End Play.
The Shims are also chamfered on one side. The chamfered side goes towards the Ring Gear.
21 Ring Gear Shims.jpg
My Shims were different sizes.
22 Ring Gear width.jpg
 

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Discussion Starter #17
Place the narrowest Shim on the Ring Gear and set it into the Case. Hold the Pinion Gear steady with one hand and rotate the Ring Gear back and forth. There should be a VERY small amount of play. This is your "Backlash".
If there is no play, you'll need to use the wider shim. you want very very little backlash, BUT YOU DO WANT SOME to allow for expansion when the gears heat up during use.
23 ring gear into case.jpg
Now put the other shim onto the Ring Gear and install the Cover with just 3 screws (23ft/lb). Check "End Play" which is the Ring Gears movement side to side. I used calipers held in a vice as pictured. Range is .004 - .008 ".
24 ring gear end play.jpg
 

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Discussion Starter #19
If you have a way to measure it, you can check backlash now. The range is .011 - .015" of play measured 3" (about) from the center of the Ring Gear axle hole. That's almost nothing (ie "very very little"). There's a tool for this, but not having it, I went with the small backlash afforded by using my existing shims. Fingers crossed (not worried)!

Now take the Cover back off and use a feeler gauge to measure clearance between the Ring Gear and the Thrust Button. It should be .002 - .004". If the gap is too large you can replace the shim under the Thrust Button with a wider one. If you need to remove the Thrust Button, it uses LEFT HAND threads (Lefty tighty) and red loctite. Heat it up. 8ft/lbs back on.
25 new thrust button (left threads).jpg
26 Ring Gear to Thrust Button.jpg
 

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Discussion Starter #20 (Edited)
Time to press in the Case Seals and Pinion Housing Seals. I coated them with Assembly Lube. They went in with even thumb pressure.
27 Case seals.jpg
There's an O-Ring around the Case Cover; I lubed it with a light coat of Assembly Lube. That O-ring is supposed to be enough for a proper seal. I did a little overkill; without getting any on the O-Ring, I used a very light coat of flexible Form-A Gasket on the Cover (the black stuff). Same with the Pinion Housing. It will make future disassembly harder, but sealing should be better. Hope this wasn't a mistake!
28 case assembly.jpg
 
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