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I notice this problem occurs on early build FJs. I drive a 6MT and would like to know when can you actually induce the rear diff to break?

when you engage in 4lo? 4hi? when you lock the rear diff? a combo of these?
or simply none of the above since 6mt is all time 4 wheel drive?

thanks for any advice.
 

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Most people have had it happen on loose uphill climbs with the locker on. One tire spins and the other will grab and get traction, causing some breakage. At least that is what i gathered from reading those threads.

This is not the only way it happens, but from what i read the most common.
 

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Discussion Starter #3
Most people have had it happen on loose uphill climbs with the locker on. One tire spins and the other will grab and get traction, causing some breakage. At least that is what i gathered from reading those threads.

This is not the only way it happens, but from what i read the most common.
thank you layonn
 

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My ring gear broke on a real steep climb on solid slickrock, in 4-Low with the rear locker engaged and A-trac on the front. Lost traction, backed-up a foot or two and gave it too much gas trying to get past the no-traction spot and spun the wheels again. eventually drove past that spot without winching but the damage was done. 8" differential, locked + heavy truck + powerful engine + too much throttle is a bad combination.
 

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My ring gear broke on a real steep climb on solid slickrock, in 4-Low with the rear locker engaged and A-trac on the front. Lost traction, backed-up a foot or two and gave it too much gas trying to get past the no-traction spot and spun the wheels again. eventually drove past that spot without winching but the damage was done. 8" differential, locked + heavy truck + powerful engine + too much throttle is a bad combination.
I think from now on until i eventually do a re-gear. If i am on a hill and it is very loose and the rear tires start to or i know they will spin, i may start turning off the locker and just try it with A-TRAC.

Aren't most people breaking the rear gear with the locker on?
 

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I've always wondered how much weight factors into the whole equation as well.

Bumping/instant traction, 35"s, pre-march '07 diffs have all been talked about, but no one has touched on whether their vehicle being 1500 pounds over the GVWR might have something to do with busting a diff as well.
 

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Being locked is the key factor in being able to damage the ring and pinion gears. The issue is complicated by the loss of traction then one wheel catches more traction than the other causing stress on the gears being locked. The other important factor is a heavy use of the skinny pedal while being locked with questionable traction.

Yes, with larger tires, there is the increased leverage that can be applied to the r/p gears, adding another factor to the equation. Re-gearing won't eliminate the chance of damaging the r/p gears nor will being outside the "questionable" build date. One can damage the gears in the early builds, the current builds as well as after a re-gear with quality aftermarket gears. In as much as there is a large amount of anecdotal evidence that the "early builds" may have questionable r/p gears, there are also 10's of thousands who are driving around w/o problems.

You can damage your r/p gear most anywhere when locked...on the street, in the mud, on the slickrock of Moab or on the granite of Rubicon. Its not hard to do, just get some wheel speed up, give it a "bump", catch a 35" tire full of traction and wait for the wonderfully horrible sound of ratcheting coming from the rear of your rig.

How not to? Don't lock your diff's unless you have a good handle on the skinny pedal, confident in your ability to maintain traction and don't succumb to those who encourage "bumping" up the obstacle when locked...
 

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I only used my locker once, a couple of years ago. A-Trac works all the time so I haven't had a need to use the locker (I don't do hardcore with the FJC). My ring broke on a paved road in 2WD fwiw.
 

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Mine broke using A-Track, climbing a slick rock formation. Heavy on the skinny, although the new one has taken much more abuse!!
 

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I have an early build 07 but have been lucky enough not to grenade the rear axle (so far). There is an incredible amount of inertia in those 2 heavy tires & wheels spinning, even if not very fast. When one tire catches it stops almost immediately and the resulting forces are transferred to the ring and pinion. If the axle is locked, there is no place to dissipate that energy. With the ring & pinion being weak, it can't help but fail.

DEWFPO
 

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I have a different theory based on my experience. The rear end is simply to small for a vehicle of that weight and power and a lot of parts are undersized and too weak given the application, adding a supercharger to mine did not help. I now have two third members with the same issue, broke ring gear you say? Nope, just one broke the gear, but both have bent carriers. One is 6/1000ths off and the other is 7/1000ths off, causing the ring gear to wobble for lack of a better term.

I believe the carrier is twisting under the load and exposing the ring gear to damage and/or failure. Non locked 3rds have additional bracing in the carrier making them structurally more rigid, that is why they are less prone to failure IMHO.

Looking back, the best way to go would have been to get an FJ without the e-locker and add a ARB air locker which is much stronger than the stock carrier.

BTW, my Yukon 4.88s have not broke, even though the carrier is bent. Just noisy now and will fail at some point.
 

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Looking to see if i can find a break down for the rear diff replacement. Came over a small incline and now the rear is making the most god awful noise. Trying to find specs and techs or replacement any help would be great. I'm a master mechanic so install is all on me so any pics or how to would be great.
 

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Looking to see if i can find a break down for the rear diff replacement. Came over a small incline and now the rear is making the most god awful noise. Trying to find specs and techs or replacement any help would be great. I'm a master mechanic so install is all on me so any pics or how to would be great.
If you've ever done a rear-end before, it's pretty straight forward, nothing unusual. It's all spelled out step-by-step with diagrams and everything in the factory service manual. You used to be able to download one for free from a post here in the forum. I bought a .PDF copy from Toyota and hard-copy paper books from someone here on the forum.
 

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Looking to see if i can find a break down for the rear diff replacement. Came over a small incline and now the rear is making the most god awful noise. Trying to find specs and techs or replacement any help would be great. I'm a master mechanic so install is all on me so any pics or how to would be great.
The easy way to do this is
Get ahold of Chase and East Coast Gear Supply. Drivetrain Specialists East Coast Gear Supply He sends you the complete 3rd member, built by them and you send back yours for a core.
The third is easy on the FJ
Drain dif, remove four outer axle bolts each side. disconnect brake line at caliper. pull axle out about 3 " each side 4 bolts on drive shaft, hang up the drive shaft with wire. disconnect electrical plug on e-locker motor over the top of the dif. Remove 14 nuts from around the dif pull out dif. E locker motor either comes out then or before you pull the dif out. Clean gasket surface and wipe out the dif. USE A OEM DIF GASKET Notice that is in bold.
re install new 3rd member and put it all back together. You will need to bleed brakes after connecting
Of course gear lube is next.
 

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Being locked is the key factor in being able to damage the ring and pinion gears. The issue is complicated by the loss of traction then one wheel catches more traction than the other causing stress on the gears being locked. The other important factor is a heavy use of the skinny pedal while being locked with questionable traction.

Yes, with larger tires, there is the increased leverage that can be applied to the r/p gears, adding another factor to the equation. Re-gearing won't eliminate the chance of damaging the r/p gears nor will being outside the "questionable" build date. One can damage the gears in the early builds, the current builds as well as after a re-gear with quality aftermarket gears. In as much as there is a large amount of anecdotal evidence that the "early builds" may have questionable r/p gears, there are also 10's of thousands who are driving around w/o problems.

You can damage your r/p gear most anywhere when locked...on the street, in the mud, on the slickrock of Moab or on the granite of Rubicon. Its not hard to do, just get some wheel speed up, give it a "bump", catch a 35" tire full of traction and wait for the wonderfully horrible sound of ratcheting coming from the rear of your rig.

How not to? Don't lock your diff's unless you have a good handle on the skinny pedal, confident in your ability to maintain traction and don't succumb to those who encourage "bumping" up the obstacle when locked...
Awesome Analogy....:bigthumb:
 
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