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

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I made a smooth tooth ring gear on my last outing, luckily the damage was just to the teeth of the gears and didn't crack the diff or anything


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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
You may be right. As I understand it the 8” diff was originally designed for 3000 lb mini trucks with 80 hp, and Toyota subsequently put it in everything, including three-ton V8 SUVS. IMO they should’ve kept using a 9.5” diff in the front like in the FJ60 for the full size Land Cruisers.
 
I’ve done some more reading on this, and I had a few more questions/points of discussion:

The 8” diff itself seems to be fairly strong and resistant to deflection. It’s the ring and pinion that seem to be the most common point of failure, though the spider gears do sometimes shear as well. This makes me question if an aftermarket locker would really make it stronger, since the R&P wouldn’t be changed.

Furthermore, if a front locker really does protect the IFS by limiting wheel spin, why did Toyota suddenly stop offering the OEM front locker in 1998? Perhaps they were concerned about the stress on the CV axles? Front lockers are usually associated with CV and front diff carnage on the 1st gen Tacoma platform, but they seem to have good results on the 100 series platform.
 
I’ve done some more reading on this, and I had a few more questions/points of discussion:

The 8” diff itself seems to be fairly strong and resistant to deflection. It’s the ring and pinion that seem to be the most common point of failure, though the spider gears do sometimes shear as well. This makes me question if an aftermarket locker would really make it stronger, since the R&P wouldn’t be changed.

Furthermore, if a front locker really does protect the IFS by limiting wheel spin, why did Toyota suddenly stop offering the OEM front locker in 1998? Perhaps they were concerned about the stress on the CV axles? Front lockers are usually associated with CV and front diff carnage on the 1st gen Tacoma platform, but they seem to have good results on the 100 series platform.

I think they ditched lockers because they thought they could mimic them with electronics (ATRAC). Software is cheaper than hardware. I think recently Toyota and other manufacturers have started to realize that there is no replacement for a good old fashioned locker, hence why they are making a comeback.
 
I think they ditched lockers because they thought they could mimic them with electronics (ATRAC). Software is cheaper than hardware. I think recently Toyota and other manufacturers have started to realize that there is no replacement for a good old fashioned locker, hence why they are making a comeback.
Yea I was just wondering why they ditched the front locker option for the pre-ATRAC 98-99s.
 
Installing a locker to the front diff removes the problem on 98-99.
The carrier might be stronger, but like I said, you’d have to reuse the R&P. The only solution to that I know of is cryogenic treatment.

It appears that the locker helps avoid “the hop” though by allowing steady throttle without having to “send it”.

The question remains why Toyota didn’t offer this solution from the factory in 98 after having front and rear lockers from 93-97.

It’s also not clear if the 4-pinion change in 2000 actually made much of a difference in strength, since breakages appear to be fairly even across years, though the lack of an empirical database on failures makes this merely speculative.

I suspect they quietly changed the metallurgy of the R&P and/or spider heard in the later years since I don’t hear about many of the 06-07 models breaking. Or maybe the VVT models are just too nice for trail use; again I’m just speculating here.
 
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.
again I’m just speculating here.

Fuel to the internet fire. Diffs, torsion bars, etc. Not sure if you're talking yourself into a 100, out, or ?
 
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Yeah, tone has been weird the whole time...almost troll-like. Or just intrinsically a half-empty type.
I’m just trying to understand the limits of different platforms, including the 100 series. It can be very hard to gauge how much of a weak point something is - one guy will swear they’re made of tissue paper since his diff gave out putting up a driveway, while just as many insist they’ve thrashed their truck for years without so much as an odd noise from down there.

It would be helpful to have more of a database of failures and how they failed, miles on the part, etc. Otherwise we’re all just sharing competing anecdotes. Lower ball joints on the 1G Tacoma are another example of this, ditto on rear diffs on the 120 platform and head gaskets on the 80 series.
 
I’m just trying to understand the limits of different platforms, including the 100 series. It can be very hard to gauge how much of a weak point something is - one guy will swear they’re made of tissue paper since his diff gave out putting up a driveway, while just as many insist they’ve thrashed their truck for years without so much as an odd noise from down there.

It would be helpful to have more of a database of failures and how they failed, miles on the part, etc. Otherwise we’re all just sharing competing anecdotes. Lower ball joints on the 1G Tacoma are another example of this, ditto on rear diffs on the 120 platform and head gaskets on the 80 series.
And I get that. But I think the objectivity you're seeking is unattainable. At least as it relates to a database of particular failures...the problem is that failures don't happen in a vacuum or with the same set of circumstances every time. It's not apples and oranges, it's apples and canned ham. Eyewitness testimony is the least reliable of all evidence available so you look for trends, percentages and probabilities.

It makes me think of this quote:

"Perfect is the enemy of the good enough."

One can drown in analysis and statistics w/o ever getting any closer to objective truth and the opportunity cost is all that time and effort.

Get what appeals to you and seems to best fit your intended use while knowing what shortcomings MIGHT pop up and be prepared for them. I think that's the best you can do.

Plus, all these conversations are muddled up between offroad performance and overall durability, two vastly different things.
 
I’ve done some more reading on this, and I had a few more questions/points of discussion:

The 8” diff itself seems to be fairly strong and resistant to deflection. It’s the ring and pinion that seem to be the most common point of failure, though the spider gears do sometimes shear as well. This makes me question if an aftermarket locker would really make it stronger, since the R&P wouldn’t be changed.

Furthermore, if a front locker really does protect the IFS by limiting wheel spin, why did Toyota suddenly stop offering the OEM front locker in 1998? Perhaps they were concerned about the stress on the CV axles? Front lockers are usually associated with CV and front diff carnage on the 1st gen Tacoma platform, but they seem to have good results on the 100 series platform.

Did toyota have a front locker in any IFS vehicle in the US at or around that time?
 
I can confirm this is solid advice. Come over to Hot Springs for the Cruiser Crawl and watch guys in FJ40s destroy their drive shafts and everything else that moves. Since my TC 3:1 4L regear to get more power, I can now shred outer OEM CV axle repza ball cages like a pro.

 
Did toyota have a front locker in any IFS vehicle in the US at or around that time?
I think they shied away from it after the 80 series since they likely weren’t sure if IFS could hold up to the stresses of a front locker, specifically the CVs. They’re only just starting to offer OEM front lockers in the newest gen Tacomas and Land Cruisers.
 

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