How widespread was the 100 series front diff issue? Did Toyota ever fix it? (1 Viewer)

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I've seen several accounts of broken front diffs on the 00+ UZJ100s, including some even on snow-covered driveways. Some have theorized it may have been the ATRAC system overloading the ring and pinion, despite the ATRAC Cruisers having the beefier 4-pinion diff. However, it's hard to get a feeling for how common these failures were, especially when many report very robust performance from their front diffs even over many miles of tough off-roading.

Also, was it limited to the early ATRAC models? I haven't seen any accounts of later 5-speed trucks having this issue, so maybe Toyota fixed it at some point.. I'd appreciate any insight.
 
98 and 99 also have a 2 pinion, just no ATRAC. And they also are not as strong as most diffs we have come to expect from Toyota. It didn't IMO have a thing to do with ATRAC.
 
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98 and 99 also have a 2 pinion, just no ATRAC. And they also are not as strong as most diffs we have come to expect from Toyota. It didn't IMO have a thing to do with ATRAC.
Wasn’t that the same diff as the 80 series though?

There have been accounts on here of 4-pinion diff failures, but they may be quite rare, idk.

Not widespread, keep in mind you're in the microcosm of Mud where most posts are things wrong. Thousands of '00+ trucks out there with no issues. No changes to Atrac or the diff after '00.
Hm, I wonder what caused the failures that did happen. Maybe a bad batch of diffs, or just luck of the draw.
 
Measures you can take to reduce chance of failure (with NO empirical data to back it up):

-Aftermarket locking differential (The diff case assembly has greater rigidity to maybe reduced deflection between the ring and pinion gear)

-Solid pinion spacer (vs crush sleeve), because it has no chance of crushing further and increasing unwanted gear backlash.

-Ring & Pinion gear cryogenic treatment, supposedly increases strength

-Part-time 4wd. Those few stories where the front diff broke while doing 'nothing.' Can't break it if it isn't connected.
 
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I won't say all, but it seems that the majority of diff breaks reported here, both 2 and 4 pinion, are from a shock type load - spinning wheel suddenly grabs traction, slamming tranny forward and back stuck in snow, etc. Not likely a bad batch of diffs.
 
I won't say all, but it seems that the majority of diff breaks reported here, both 2 and 4 pinion, are from a shock type load - spinning wheel suddenly grabs traction, slamming tranny forward and back stuck in snow, etc. Not likely a bad batch of diffs.
Yea I was just confused since some seemed to be happening in extreme off road situations where it’d be somewhat expected, but others apparently blew in just a few inches of snow.

Also, I wonder why the 2-pinion diff doesn’t see as many issues in the 80 series (except in reverse).
 
Yea I was just confused since some seemed to be happening in extreme off road situations where it’d be somewhat expected, but others apparently blew in just a few inches of snow.

Also, I wonder why the 2-pinion diff doesn’t see as many issues in the 80 series (except in reverse).

The mechanism of the break is the same between off road or snow. High wheel speed combined with sudden traction shock loads the driveline and something lets go. Typically it's the diff or a CV.

I would also argue that while the 4 pinion diff of the 2000+ is stronger, the 2 pinion of the 98-99 isn't fragile by any means and not a time bomb waiting to explode.
 
Also, I wonder why the 2-pinion diff doesn’t see as many issues in the 80 series (except in reverse).

The 2 pinion isn't a problem in the 80 series or the early 100 series. The 100 series "problem" is just one of those myths that never goes away. People can't get their head around the fact that the "more robust" 4 pinion is under-engineered for the enormous stresses of A-Trac. Toyota screwed up.
 
The 2 pinion isn't a problem in the 80 series or the early 100 series. The 100 series "problem" is just one of those myths that never goes away. People can't get their head around the fact that the "more robust" 4 pinion is under-engineered for the enormous stresses of A-Trac. Toyota screwed up.
Interesting, so it’s kinda like the 80 series head gasket hysteria. Sometimes I wonder how notions like that develop. It’s like a few people have issues and then go around complaining about it on all the forums until everyone is convinced it will happen to them.
 
Interesting, so it’s kinda like the 80 series head gasket hysteria. Sometimes I wonder how notions like that develop. It’s like a few people have issues and then go around complaining about it on all the forums until everyone is convinced it will happen to them.
This is an offroading forum that’s why you see so many threads about these diffs breaking. Your front diff is not gonna break during normal every day driving. It breaks when you’re trying to go over rocks, or any slippery surface where you get wheel spin/wheel hop. It’s pretty wide spread, not just an empty rumor. It’s definitely a weak link in these cars, that’s why you see so many failures from people that go off road all the time.
 
Aside from
I won't say all, but it seems that the majority of diff breaks reported here, both 2 and 4 pinion, are from a shock type load - spinning wheel suddenly grabs traction, slamming tranny forward and back stuck in snow, etc. Not likely a bad batch of diffs.
This.
And it’s not just the shock load aka death hop that causes 9 out of 10 front diff failures, the remaining is how to use the steering wheel to avoid this. Full lock left or right trying to crawl up and slipping is a perfect recipe for front ring & pinion failure regardless if it was 2 or 4 pinion open diff. Plus the fact that the 100 series is 5,000 lbs - weight is true adversary.
 
Aside from

This.
And it’s not just the shock load aka death hop that causes 9 out of 10 front diff failures, the remaining is how to use the steering wheel to avoid this. Full lock left or right trying to crawl up and slipping is a perfect recipe for front ring & pinion failure regardless if it was 2 or 4 pinion open diff. Plus the fact that the 100 series is 5,000 lbs - weight is true adversary.
I’d always heard full lock and slipping puts more stress on the CVs as opposed to the diffs. But maybe the 100 series CVs are strong enough to make the diff the fuse in such situations.
 
This is an offroading forum that’s why you see so many threads about these diffs breaking. Your front diff is not gonna break during normal every day driving. It breaks when you’re trying to go over rocks, or any slippery surface where you get wheel spin/wheel hop. It’s pretty wide spread, not just an empty rumor. It’s definitely a weak link in these cars, that’s why you see so many failures from people that go off road all the time.
Sure, if you push it off road you’ll find the limits. But like I said earlier, some of the breakages have been observed on slightly snowy driveways, which is what I’d call normal everyday conditions: the kind of thing my old 99 Forester could do effortlessly. These seem like abnormal failures for a vehicle which otherwise is the ultimate expedition/touring platform.
 
idea: use engineered low torque (lower that torque needed to blow diff/axle spline) shear bolts at the driveshaft/trans case interface. if failure, just rebolt w. spare bolts.

Once sheared, drive shaft would just drop. Might need a drive shaft cage to prevent wild spin induced damage to other structures.

'course, there are always the unitended consequence like misclocked rebolted shaft alignment causing ds vibrations or ?
 
On the IFS Toyotas I have had, Toyota seemed to have kept the failure point as the CV. The 100 is the first where the diff seems to go before CVs do.

IMO an easier solution would be a sheer pin in the hub flanges, or just moving to a softer hub flange material and have them be a wear/replacement item every 60k service.
 
On the IFS Toyotas I have had, Toyota seemed to have kept the failure point as the CV. The 100 is the first where the diff seems to go before CVs do.

IMO an easier solution would be a sheer pin in the hub flanges, or just moving to a softer hub flange material and have them be a wear/replacement item every 60k service.
From the videos I’ve seen it seems like the CVs were the fuse again on the 200 series when pushed to the limit. I wouldn’t want to have to change an IFS front diff on the trail, that’s for sure.
 
I broke my 98 and saw how easy an 03 snapped. Honestly I think all are just as weak and the 2 vs 4 pinion thing is just a made up thing here on Mud. My 98 being fully built (heavy) and my friends with just suspension and tires.
I have done the same obstacle like 50 times without any issue, the 03 first time and snapped.

20210925_151140.jpg
 
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I broke my 98 and saw how easy an 03 snapped. Honestly I think all are just as weak and the 2 vs 4 pinion thing is just a made up thing here on Mud. My 98 being fully built (heavy) and my friends with just suspension and tires.
I have done the same obstacle like 50 times without any issue, the 03 first time and snapped.

View attachment 3335414
So you're saying your 98 100 series front diff held up better over time, despite being the supposedly weaker 2-pinion unit? This might support the theory that ATRAC could put too much stress on the front diff, even in stock form and on mild terrain.

It's also worth pointing out that I don't hear about these front diff failures on other ATEAC-equipped trucks like the 5th gen 4runner, Lexus, FJC, etc., so maybe it was some kind of teething issue with the first ATRAC systems in the early-2000s UZJ100s.
 
So you're saying your 98 100 series front diff held up better over time, despite being the supposedly weaker 2-pinion unit? This might support the theory that ATRAC could put too much stress on the front diff, even in stock form and on mild terrain.

It's also worth pointing out that I don't hear about these front diff failures on other ATEAC-equipped trucks like the 5th gen 4runner, Lexus, FJC, etc., so maybe it was some kind of teething issue with the first ATRAC systems in the early-2000s UZJ100s.
Yeap, my "weak" 98 diff held up 5 years of wheeling including Moab and the Whipsaw trail without absolutely and randomly broke a few teeth in a mild/easy obstacle with almost no wheel spin or throttle input.
My buddy's 03 snapped the 2nd time he took it out to the same trails I have been doing for years and broke there.
Early FJ Had a similar issue on the rear end having smaller diameter ring gear and not holding up to the weight of the truck.
Our 100's just weigh too much for the size of gears it has IMO
 

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