Bad Day on Trail - likely rear differential stripped and broken CV

[jblinga]

People always say stuff like that when they don't actually wheel. I always hear this from people who who own range rovers or have never been over an obstacle with their truck before. If you do not have to pound your skidplates that you have reinforced with 1/2" thick plate back into shape with a sledgehammer after you get off the trail, you are not really rock crawling, I consider that just "driving". So yeah, if you are "driving" off road over a few pebbles you will never break a differential. I broke a CV axle simply by putting my truck into Drive when I was in 4lo before trying to get off a 5' tall rock. I have no delusions of grandeur when looking at the drivetrain of a 4th gen. The v8 in the 4th gen 4runner has more power than a Ford Super Duty Triton V8 and the ring gear is SMALLER. That combo is a recipe for disaster, so I would rather not hear from someone who wasn't there that its only "driver error" for all the thousands of people who have had the exact same problem with the exact same vehicle in the exact same circumstances. The fact is that the rear differential design for the 4th gen v8 4runner design is horrible, the ring gear from a 90hp truck should not be used on a 270hp truck at any time, yet that is exactly what has happened and every person who attempts to wheel with it is going to break it.

Trust me guy, I wheel. I live near southern Utah and I'm rockcrawling when I'm out there. Dragging on my fuel tank skid dragging my trailer receiver coming off obstacles and barely have clearance everywhere else. I run loaded down with a ton of gear for emergency situations and camping etc. I've spent a ton of time offroad and I just laugh and shake my head when people just send it to compensate for lack of driver skill. I'm not arguing that the 4th gen rear is bulletproof, only that if you know the drivetrain's limits you won't put yourself in jeopardy of blowing shit apart. Worst thing you can do is just floor it to make up for taking a shitty line, not having diff lockers or just flat out not having the skill/common sense to know when you're stressing the drivetrain beyond it's capability. But we all know the interwebz are full of arm chair warriors who have a master's in engineering.

**** what do I know right...? I just drive in mall parking lots all day

 

[Bumbo]

It's not necessarily the torque that is the reason for breaking diffs on our rigs, its the amount of wheel spin and speed due to the lack of an actual low range that a crawlbox or aftermarket tcase can provide. Lower gearing in the t case multiplies torque (think 2x, 3x or more) but allows you more control and time to stop if your tire gets bound in the rocks. I think lockers and lower diff gears help because ATRAC relies on wheel spin to some extent but the next level of durability is a lower t-case or a Diamond w/9.5" LC gears or Currie w/Ford 9", the t-case being the cheapest especially if you've already dumped money into locking/regearing the front and rear.

Edit: and the 5th gen/later FJ "8.2" rear ends (I believe) have the same size gears as our 8" the carrier is just strengthened, which I believe makes the gears just strong enough to outlast the axle shafts in those diffs, so now you'll break axle shafts. How much stronger does that make it? No idea. I wouldn't spend much money on swapping over to one of those when you can get a fully loaded Currie + F9 or D60 with so much more benefits.

I talked to Currie last week to learn about some options...

I wanted to know what options they offered and what makes them different or a better/stronger option. It's a costly option, but I liked what I was hearing.

It's not just rear end strength, but we basically discussed building an axle of custom length which would match the track width increase of a long travel setup without needing to use things like wheel spacers. After a phone conversation with them, I was convinced this was the route if I was going all-in.

If you consider building something in a custom length doesn’t really cost any more than a regular axle, I started to see more and more value in going this route when trying to take the truck to that next level.

 

[Inv4drZm]

I've spent a ton of time offroad and I just laugh and shake my head when people just send it to compensate for lack of driver skill. I'm not arguing that the 4th gen rear is bulletproof, only that if you know the drivetrain's limits you won't put yourself in jeopardy of blowing shit apart.

I see you have 33's, have you broken a differential yet? Everyone that I have seen (this thread excluded) once they moved up to 34s or 35s is when the diff gives up.

It's difficult to truly know the drivetrain's limits without breaking stuff once in a while. Throw on a set of 35's with a diff that has 150k miles and it is all too easy. Sometimes shit happens whether you baby it or not.

There are some that take it easy on medium trails and there are others the 8" isn't enough for the trails they want to do and they don't like babying their gear. Fortunately there are upgrades. Please disregard the idiots that make the medium trails look difficult.

 

[Drunner97]

I see you have 33's, have you broken a differential yet? Everyone that I have seen (this thread excluded) once they moved up to 34s or 35s is when the diff gives up.

It's difficult to truly know the drivetrain's limits without breaking stuff once in a while. Throw on a set of 35's with a diff that has 150k miles and it is all too easy. Sometimes shit happens whether you baby it or not.

There are some that take it easy on medium trails and there are others the 8" isn't enough for the trails they want to do and they don't like babying their gear. Fortunately there are upgrades. Please disregard the idiots that make the medium trails look difficult.

I was on 33s when I blew mine out. The 35s didn't come until after I regeared.

 

[duffdog]

I talked to Currie last week to learn about some options...

I wanted to know what options they offered and what makes them different or a better/stronger option. It's a costly option, but I liked what I was hearing.

It's not just rear end strength, but we basically discussed building an axle of custom length which would match the track width increase of a long travel setup without needing to use things like wheel spacers. After a phone conversation with them, I was convinced this was the route if I was going all-in.

If you consider building something in a custom length doesn’t really cost any more than a regular axle, I started to see more and more value in going this route when trying to take the truck to that next level.

If I'm not mistaken, the 80 series LC rear axle is the right width and comes with a 9.5" gearset (and optional elocker). You might be able to snag one of these from an old LC for a lot less money.

 

[Inv4drZm]

If I'm not mistaken, the 80 series LC rear axle is the right width and comes with a 9.5" gearset (and optional elocker). You might be able to snag one of these from an old LC for a lot less money.

Offset pumpkin. At the very least would need a new driveshaft. I wouldn't think it would be easy.

 

[duffdog]

Offset pumpkin. At the very least would need a new driveshaft. I wouldn't think it would be easy.

Oh yeah...right. I've never had one in front of me so I didn't realize that. I have one of the Tundra 9.5 axles in my garage that I might use for the 4r, but I will have to get the axle shafts redrilled for 6x5.5. The tundra 9.5 axle can sometimes be had for free as Tundra guys like to upgrade to the 10.5.

 

[Mutant138]

I believe I had two tires off the ground and they were free spinning and then I lost uphill momentum. I was in 4 low. Probably used too much skinny pedal - I think when I came back down is when it regained traction and the CV broke and diff blew at the same time.

The trail was Miller Rock west out of Lyons, CO. Rated 5/7 and I believe I was on the gnarliest part when this happened. Probably should have just got a tow strap to get over this part (hindsight is 20/20).

Could have literally been spinning everything too fast. I blew up a drive shaft on a vortec swapped c10 when up put too much throttle when on jack stands (long story short I was a rookie mechanic and I made a poorly calculated risk to save time. Spoiler...I didn't save any time).

Edit: NVM I see that it's common on the 4th G. Weak rear ends.