8.2" Rear Axle Upgrade

BMThiker

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I recently ate another set of gears in my '07, and they were only a few months old. Decided that the axle housing is cursed (or more likely bent) and it was time for an upgrade. Researched some of the more popular options: 8.2" out of a newer FJC/4R, Nitro/Diamond 9.5" and Currie Rock Jock. Went through several options of how to rebuild the diff with a locker, if I had to use a non locking axle assembly. I ended up talking to Nitro and East Coast Gear to analyze cost with all options. Decided the best option for me was the 8.2" because it was the most affordable, kept things mostly unchanged as far as OEM parts and because it was the most affordable 😁

So I went on a hunting expedition for a junkyard axle that wasn't on the other side of the world. Harder than you think. I found a 2012 4R axle that actually turned out to NOT be the right thing. He told me it was an e-locker axle, but he misinterpreted the VIN decoder that said it had a center diff lock (ie 50/50 tcase in 4Lo). Found 2012 FJC axle in Grover, NC and had it delivered. They didn't know much at all about the truck and the pictures looked like the truck had rolled, so it was not my top pick, but it was the only pick available right now.

RearDiff-pt3 (1).JPG
 

BMThiker

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Finally got the 8.2" rear axle in place. I kept my brakes and wheel sensor harness. Chunky 3rd got rebuilt last weekend with 4.56 gears.

Fun fact, the axle shafts are identical except for the bore diameter where the rotors seat on the hub flange. They made a lip on the flange just about 1-2mm larger, so the rotors are specific to model years on this axle. The wheel bore is still the same, just not the rotor bore. I didn't want to replace the rotors, so I just reused my axles. Also, I have recently rebuilt both of my axles, so the maintenance history is known on them. On the new axle, the junkyard couldn't tell me how many miles were on it, and from disassembly, looks like they have never seen a bearing replacement. The other thing is the swaybar is different. Larger mounts on the axle tube and slightly different location of the mounting plates. Running willy-nilly at the moment, but new swaybar is not cost prohibitive.

Here's what's identical on the 8.2" axle to the 8" counterpart:
  • linkage brackets/bolts
  • shock mounts/bolts
  • axle shaft length/spline, mount flange/studs
  • dust shield
  • e-brake parts
  • calipers
  • hard brake lines
  • soft brake lines up to crossmember
  • wheel sensors & harness
  • wiring harness to e-locker actuator & lock position sensor
  • lock position sensor itself
The e-locker actuator motor looks identical except for the bored out holes where it mounts to the housing - from M8 to M10 size studs in the housing.

I had to ditch the e-brake because apparently the junkyard environment had allowed the drum brakes to rest/rust in place against the inner rotor surface. I ended up chiseling the parts and cracking the rotor on the passenger side. This e-brake design is from satan himself and needs to die. They use the same design on the 100 series too. Eventually, I will install a t-case output shaft caliper to use as an e-brake.
Rear8.2axle (1).JPG

Everything had a fresh coat of "just paint the f**k over it" black. One of the other reasons I didn't want to swap these calipers over. I did strip it of all brake lines, wiring, clips, bolts, etc to have as spares. Even the axle shaft assemblies will serve as spares. I might see if I can machine that lip off the hub flange though.
Rear8.2axle (2).JPG
Rear8.2axle (3).JPG


Rear8.2axle (5).JPG


Rear8.2axle (6).JPG
 

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More pics of the installation.
Rear8.2axle (4).JPG

New gears installed last weekend.

Rear8.2axle (20).JPG

New chunky 3rd is a lot thicker at the mounting surface.

Rear8.2axle (21).JPG

New housing looks to be a bit thicker at this area too.

Rear8.2axle (24).JPG

After carefully disconnecting everything, I left the linkage, wiring harness and the brake system plumbed during the extraction of the old axle. The only way you can do this is to slice the brakeline mounting bracket at the hub ends, carefully bend the metal bracket open so the still connected soft line/hard line juncture doesn't need to be disassembled.

Rear8.2axle (25).JPG

Old axles and rotors waiting for reinstallation.
 

helocat

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Dang Rick that's some solid work right there. Better on the rack than the side of the trail, good planning for DigDug.

Mark
 

abuck99

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Appreciate you taking the time to write this up. 👍👍I suspect that I'll be on the same path at some point and this helps a lot. Whats the key reason you chose 4.56 vs 4.88? Carrier limitation?
 

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Never needed more reach than 4.56 gives me with 34-35" tires. Does reasonably well at highway speeds cross country. 4.88s would be better on the trails no doubt, but this is still my daily driver.
 

BMThiker

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Got back to the garage last night to strip down the old axle of all usable spares. Here's a closeup of the axle flanges on a 8.2" axle. Note the extra lip where the rotor seats (especially rusty in this case).
Rear8.2axle (17).png



Also tried to see if the old housing looked noticeably bent. It does not, to the naked eye, anyway. Makes me think the 8" carrier itself is flexing, or the housing is flexing & causing the carrier to flex...I've heard that theory floated before.
Rear8.2axle (22).JPG



Can't do anything without busting some knuckles!
Rear8.2axle (18).JPG
 

abuck99

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So if the theory of “housing-flex” is im fact true, Im wondering if trussing the 8” housing would be a possible solution as a budget friendly option instead of a 8.2 (or larger) axle swap for up to 34/35” tires? I think the jeep guys with Dana44’s who upgrade to 35~37’s use the truss option ahead of jumping up to Dana 60 rear end.
 

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For the time and effort, I would just find a junkyard 8.2" like I did. I honestly feel the 8" rear axle was adapted from the mini-truck platform and never engineered properly for the weight of our trucks.
 
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For the time and effort, I would just find a junkyard 8.2" like I did. I honestly feel the 8" rear axle was adapted from the mini-truck platform and never engineered properly for the weight of our trucks.
A reasonable hypothesis based on Toyota upgrading on later models, and the dimensional differences.

I've been debating upgrading to the 8.2 for a while now even before seeing your post. It sounds like, with the exception of a few hiccups, it's a bolt in proposition - so following with interest.
What's kept me firmly on the fence is do I go for a proper long travel set up such as Chaos, All-Pro or now the new Marlin Crawler RCLT (hopefully soon to be released) eventually, and if so just have a rear Diamond made to match the front track of an extended long travel.
 

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From a junkyard, less than $2K delivered. I think I was $1850 out the door. First axle I found was listed for only $1650 (but unavailable). You might get lucky. I used www.car-part.com to search.
 

BMThiker

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I recall 2010 & up with e-locker will work. The car-parts site will search for interchange parts as well. So if you plug in 2010 FJC rear axle for the search, it will also search for compatible 4R too.
 

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As far as updates go... I've had some gear noise over the past couple weeks. I crawled under the truck a couple weekends ago and some of my nuts had backed off around the third member. Not falling off, but not still torqued, which surprised the hell out of me. I've only daily-ed it the the past month or so. Added loc-tite to the studs and torqued everything again.

Out of an abundance of caution I decided to pull the third for inspection this past weekend. Everything looked good on the gear meshing and the backlash was about 9/1000. That's on the upper end of the specs so I decided I wanted it to be a bit tighter. I moved the carrier bearings until it hit about 7/1000. Reinstalled everything and loc-tited the hell out of everything. New gear oil and sounds much quieter now. Hopefully that's the end of story for a while.
 
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