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Yeah but what do you do once it is out of Warranty. Seems Toyota should cover this untill the fix the REAL problem, poor design?
 

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I hear you! So glad I didn't buy an FJC when I was looking at them (Melanie and I both independently test drove one the same week, and when we each found out that the other had gone down to drive one, we were really close to buying one). I still really like sporty look of them. But I am happy with the Tacomas.

I suppose there's an extended warranty option? But if it were me, the first time it blew after the warranty ran out, I'd take it to Zuk or some other highly experienced gearhead and pay them to do it right with lower gearing and see if an ultraprofessional install and lower gears makes any difference. I'm guessing there's a little slop in there somewhere, or something misaligned just enough that under torque it gives? Maybe a weakness in the ring gear material? ... and a proper setup with shims, aftermarket R&P, or whatever is necessary would make a difference. If a professional install and new lower gears doesn't work, if you want to keep the FJC, I'd do an axle swap to something beefier and go to 35's. Regearing every 5 months is totally unacceptable. I agree with you, Molly. Toyota should redesign and do a recall.
 

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If I would fit comfortably in a Tacoma, I'd probably have one, but the inside of the FJ is sooooo much nicer with head/shoulder/leg room for me. That and it stays nice and cool with the vertical windscreen and white roof/light color. Other than the rear-end, I have had ZERO problems that weren't driver/abuse induced and I've gone places I never have gone before. When the time comes it would be cool to look at the axles on the new Tundras :D
 

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Well, there is nothing technically wrong with this differential. What was wrong was the weight of the vehicle compared to the size of the differential. This rear differential is only a 8", just like the ones installed in the e-locker Tacoma and 4runner. It uses the same size bearings and internal parts used in the V6 8" all the way back when they first starting putting them in the turbo trucks. Even the new v8 4runners use the 8" differential, they have a low failure rate due they have a very low frequency of off road use.

The only stronger differential to install would be the 8.4". You loose the e-locker option, you gain a "bridge" over the bearing caps. This "bridge" adds extra strenght against case spreading. Good luck with that housing though, welding all the brackets on a Taco housing in the same place as a FJ might suck.
 

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If I would fit comfortably in a Tacoma, I'd probably have one, but the inside of the FJ is sooooo much nicer with head/shoulder/leg room for me. That and it stays nice and cool with the vertical windscreen and white roof/light color. Other than the rear-end, I have had ZERO problems that weren't driver/abuse induced and I've gone places I never have gone before. When the time comes it would be cool to look at the axles on the new Tundras :D
That totally makes sense to me, given your size. When I drove it, the first thing that struck me was how unnecessarily high the dash and roof are, how small the rear window is, and how high the side windows in and behind the doors are. Add it all up and I felt too short in it, like the seat needed to go up, not forward, but up. Visibility was terrible for me, and I'm almost 5'11". Mel is only 5'4", and she said she felt like she couldn't see out of it well enough to drive it safely. So at your stature, that makes total sense - it just fits you better.

Based on the last post, it sounds like the solution instead of beefing the rear axle and diff is trimming the fat on your FJC. Seeing as how wheelers tend to add weight in armor, etc, I doubt that's a very practical solution. Guess you could remove the back seats and save 50-60lbs? Not gonna help much. Yeah, like I say, putting in a new R&P every 5 months wouldn't work for me.

What do the massive SASed FJC's run for the rear end to get around this weakness? Ford 9-inch? Diamond Axles? Tundy Axles? There's gotta be a solution. These fabricators are highly skilled and creative people who work magic in their shops... assuming you've got the green, I'd be willing to bet someone out there would be able to put in a beefier rear diff/axle for you. Like the fatkid says, it might suck making another axle work, but if you really like the rig and really don't want to keep replacing the R&P, and you're gonna keep wheeling it like you do, seeking out a solution is just something you're going to have to do some day. Good luck.
 

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With high gear ratios (like 3.73), the ring gear is the weak point, with low ratios (like 5.71) the pinion becomes the weak point. SO if you need maximum strength, it seems 4.56 or 4.88 is the sweetspot.

Eric - I think there's a lot that could be done to help the rear R&P survive. First would be to truss the axle housing, with a specific focus on keeping the ring the third bolts to from deflecting at all. Next would be a real front locker - I think the herky-jerkiness of the ATRAC acts as a damage multiplier by shock loading the drivetrain.
 

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The strength comes from the amount of tooth contact. For example a 3.73 pinion has more teeth therefore giving more surface area contact to the ring gear. Where as a 5.38 has a very small pinion gear and way less teeth, which in turns means less contact and more force placed on each tooth.
 

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Not true - all will have 3 teeth in contact at any given time. The fewer teeth on the pinion make lower gears much more difficult to setup properly to ensure that proper contact though. The number of teeth also drives the diameter of the pinion and the thickness of the ring gear. I think it's funny when people on forums recommend people go with 5.29's instead of 5.71, when they both have 7 tooth pinions (and therefore almost identical dimensions)

See the link to Zuk's website above for pictures of the dimensions.
 

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Its the bearing cap bridges that need to be there, or, as Brian said, a larger diff.

Trussing the axle won't help, as the flex is internal to the third. Its literally the carrier bearing towers flexing away as the pinion drives into the ring gear.

IMO, go with a ford 9 for the rear. That'd be a sweet axle to run.

And x2 on that front locker. I know a lot of folks swear by that ATRAC, but its always seemed really sketch to me. I don't like the helter skelter jerkyness of it. Too much intermittent load for my liking.
 

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Not true - all will have 3 teeth in contact at any given time. The fewer teeth on the pinion make lower gears much more difficult to setup properly to ensure that proper contact though. The number of teeth also drives the diameter of the pinion and the thickness of the ring gear. I think it's funny when people on forums recommend people go with 5.29's instead of 5.71, when they both have 7 tooth pinions (and therefore almost identical dimensions)

See the link to Zuk's website above for pictures of the dimensions.
Now I understand that the force is transfered across 3 teeth. Obviously. One coming into contact, one in direct contact, then one losing contact. With the larger pinions having more teeth and a larger radius the transfers are closer together making for a better sharing of force. This is just focusing on tooth strength though, but that seems to be the failing point.
 

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That totally makes sense to me, given your size. When I drove it, the first thing that struck me was how unnecessarily high the dash and roof are, how small the rear window is, and how high the side windows in and behind the doors are. Add it all up and I felt too short in it, like the seat needed to go up, not forward, but up. Visibility was terrible for me, and I'm almost 5'11". Mel is only 5'4", and she said she felt like she couldn't see out of it well enough to drive it safely. So at your stature, that makes total sense - it just fits you better.

Based on the last post, it sounds like the solution instead of beefing the rear axle and diff is trimming the fat on your FJC. Seeing as how wheelers tend to add weight in armor, etc, I doubt that's a very practical solution. Guess you could remove the back seats and save 50-60lbs? Not gonna help much. Yeah, like I say, putting in a new R&P every 5 months wouldn't work for me.

What do the massive SASed FJC's run for the rear end to get around this weakness? Ford 9-inch? Diamond Axles? Tundy Axles? There's gotta be a solution. These fabricators are highly skilled and creative people who work magic in their shops... assuming you've got the green, I'd be willing to bet someone out there would be able to put in a beefier rear diff/axle for you. Like the fatkid says, it might suck making another axle work, but if you really like the rig and really don't want to keep replacing the R&P, and you're gonna keep wheeling it like you do, seeking out a solution is just something you're going to have to do some day. Good luck.
FYI, the seats do jack (a lot) up as well as fore and aft. I tend to pump it up a couple of inches when off-road to increase visibility. Of the few SA FJs I've seen I think Diamond Axles are the favored replacement, but I think there are a few different setups rolling around. LIke I said the new Tundra rear looks nice. Weight loss has been on my to-do list, but little time and money have prevented my dream from coming true :p

With high gear ratios (like 3.73), the ring gear is the weak point, with low ratios (like 5.71) the pinion becomes the weak point. SO if you need maximum strength, it seems 4.56 or 4.88 is the sweetspot.

Eric - I think there's a lot that could be done to help the rear R&P survive. First would be to truss the axle housing, with a specific focus on keeping the ring the third bolts to from deflecting at all. Next would be a real front locker - I think the herky-jerkiness of the ATRAC acts as a damage multiplier by shock loading the drivetrain.
Oddly, the ATRAC by itself is very effective in many situations, but you might be right that in conjunction with the rear locker it might be detrimental, especially when pushing all that weight. I wonder if that's why they kept them independent in the first run FJs? I hacked mine (shhh), but the next iterations (late 07s and 08+) all have the ability to use both simultaneously without the hack...
 

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Eric, it looks like you rear differential was rebuilt previously. I found some marks that are not "Toyota" on the bearing caps and pinion nut. Not sure if it is a true measurment but the backlash is around .013" on the good part of the ring gear.
 

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Eric, it looks like you rear differential was rebuilt previously. I found some marks that are not "Toyota" on the bearing caps and pinion nut. Not sure if it is a true measurment but the backlash is around .013" on the good part of the ring gear.
That's curious.
 

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Eric, it looks like you rear differential was rebuilt previously. I found some marks that are not "Toyota" on the bearing caps and pinion nut. Not sure if it is a true measurment but the backlash is around .013" on the good part of the ring gear.
That's curious.
No kidding. I wonder if they regeared your third member (and did it poorly) instead of ordering in a new Toyota-built one. Are they Toyota gears, or somethng aftermarket? That's probably the only recourse you would have regarding the warranty as I'm sure it has "repair or replace at Toyota's option" in the fine print somewhere.

Trussing the axle won't help, as the flex is internal to the third. Its literally the carrier bearing towers flexing away as the pinion drives into the ring gear.
Agreed, but it's all one big chunk of metal - at some point that deflection translates to the mounting ring, and if you can hold that better, you minimize the amount the the third itself can move. Diamond housings build this mounting flange out of 1/4" for this reason.
 

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Too bad Toyota didn't copy the Ford 9" and their pinion support. I think alot of Toyota 8" problems would be solved with that extra support.

Here's what both of my 8" diffs look like after 2 years on 40's


The pinion deflects alot when you add big tires, ultra low gearing, and weight.
 

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Having first hand knowledge of the weight that Eric's Truck could loose(Doug and I were digging in the back for something he needed while he was on the first obstacle) YOu could easily shift 100 lbs. out of the rear end of that rig. :D

But then again you may not have anything to support trail repairs.:(

Oh hell Eric just buy a trail trailer to pull behind your FJ and this way it will keep you light.

I guess that's why there wouldn't be AS big of an issue on the later model Taco rear ends. With the composite bed and thin sheet metal cab I practically blow away in the wind. :p I swear if all 4 wheels were on ice I could slide the truck sideways by myself. :eek:

Oh yeah!!! I am fixed! New rear cover and about a day of work. It was neat to see how the inside of the case was. Thanks fatkid!!

I am saving the cover for now but a good point was brought up - It would make a killer carnage trophy if mounted on a base. We could give it away each year at the Christmas party. Hmmmm......
 

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well looks like it would have been a good time except all the carnage!
 

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Having first hand knowledge of the weight that Eric's Truck could loose(Doug and I were digging in the back for something he needed while he was on the first obstacle) YOu could easily shift 100 lbs. out of the rear end of that rig. :D
I saw that sitting behind him waiting for a go at it while you guys were digging and thought to myself 'Holy Shit!'. I think he's got everything but the sink!
 

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http://image.mustangmonthly.com/f/18153604+w750+st0

The pinion deflects alot when you add big tires, ultra low gearing, and weight.[/QUOTE]

:eek: Thats what my front ARB carrier looked like chewed up like that! Pinion deflection is doing that? Im only on 35's WITH a Diamond housing, 4:88's! :eek: Everything you guys mentioned on this thread (that I picked up) Ive done that "should" have prevented this. What gives? My rear does not show this problem.

So what we did was clearance the casing by using a flap wheel to take it down to the low spots, and also took a bit off the pinion gear. It clears now anyway.

I thought it was a bad setup on the gears, but the pattern was good. So removing material seemed like the way to correct it. :confused:
 
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