rear diff troubles

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DBS311 said:
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Some 80 guys have been finding that their electric lockers (I know, different diff) break with 37"+ tires and they move to the ARB.
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On the 80 it's the axle and design of the locker. When an axle is twisted, broken it becomes very difficult to remove the diff, most of the time requiring surgery on the housing. The locker is undamaged, it's an axle, locker cog gear design issue, unrelated to the 8" diff design. Yes going to an ARB and non locker type axle solves the problem, but the 80 axles are pretty stout and very few have ever pushed them hard enough to break them. The front 8" hi-pinion, a design more closely related to the FJC rear, have proven very reliable.

The best theory on the rear failure that I have heard is that they are being setup from the factory with less carrier bearing preload. This allows the carrier/ring gear to deflect, move more, leading to failure. Don't have a clue why, maybe for less rolling friction, but the newer "looser" ones are failing and the basic design is the same as all 8" mini diffs that have been a long term proven design.

http://www.gearinstalls.com/refresh.htm

http://www.gearinstalls.com/freshen.htm
 
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I can comment some on the problems with the TT FJ's. We did have some early failures with the rear diffs( 2 diffs on 1 fj and 1 diff on 1 fj) So out of 6 wheeling trucks that were wheel fairly hard and alot(we did about 94 days of wheeling on the central team) Chris never had a failure and I had one. The east coast team never lost a rear diff that I remember. The west coast team had one truck that lost 2 diffs. Toyota thinks some may be in a heat treating process that was used and has changed the process for the better. I have not heard about Kevin's theory, but I would think it could contribute to the loss of teeth with the right load. We did not loose a rear diff on the rubicon or brake any thing on the rubicon with TLCA. As for the TTORA event, I believe it was a owner(not any Trail Team FJ's) that damage the rear diff as well as the body on that trip.
Hope this helps, later robbie
 
Thanks for clearing that up Kevin. I went wheeling with a bunch of 80 guys up at Big Bear and they were mentioning to me that for strength reasons the ARB was the way to go for 37"+ tires. I didn't ask what was actually happening to the internals of the rear axle. Good info to know.
 
I can't see how a inch pound or two less preload will cause the entire carrier to deflect enought to destroy a ring gear. I always measure pre load when I pull apart a third and some come in so loose you can actually move the carrier laterally on the bearings.
And 40's 60's and 80 leave the inner splines stuck in the third as the axle breaks where it tapers down. Nothing new here.
That said, there is only one reason for this type of failure.
The manufacturing process.
 
saskdiesel said:
I can't see how a inch pound or two less preload will cause the entire carrier to deflect enought to destroy a ring gear. I always measure pre load when I pull apart a third and some come in so loose you can actually move the carrier laterally on the bearings.
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In my limited experience "some come in so loose you can actually move the carrier laterally on the bearings" would greatly reduce the strength of the gear setup when used offroad.

None of the observations in my post above are from Toyota. I have been doing research to regear my 80. Talking to local gear installers, their experience is that tighter carrier bearing preload makes for a stronger setup and it's their observation that some units are coming setup looser than they would like to see for offroad use. Their standard procedure is 100 ft/lb for units that see highway use and up to 200 ft/lb on the adjusters on trailered units.

One was telling me of a customer that broke a ring in a late e-locked Taco, towed to the dealer and replaced the 3rd with an new assembly under warranty. Brought to his shop, dropped the 3rd and it had no preload, he said they turned the adjusters 2 notches before any preload was felt and ended up with about 4 notches on each side. I haven't measured the thread pitch on the adjusters, but that's about a half a turn total, a significant adjustment IMHO.

Randy's R&P take on carrier preload;

http://www.ringpinion.com/TipOfTheDay.aspx?TipID=11
 
Tools R Us said:
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Their standard procedure is 100 ft/lb for units that see highway use and up to 200 ft/lb on the adjusters on trailered units.
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I have no idea what this comment is refering to?
100 foot/lbs of pre load?
That makes no sense.
Pre-load in any diff is measured in inch pounds. On a Toyota diff usually this is under 25 inch pounds for new bearings including the pinion seal. I usually set up used thirds at about 15 inch pounds.
As you see this is under 2 ft/lbs of torque.
 
saskdiesel said:
I have no idea what this comment is refering to?
100 foot/lbs of pre load?
That makes no sense.
Pre-load in any diff is measured in inch pounds. On a Toyota diff usually this is under 25 inch pounds for new bearings including the pinion seal. I usually set up used thirds at about 15 inch pounds.
As you see this is under 2 ft/lbs of torque.
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They are applying that much torque to the carrier bearing adjuster nuts, I didn't mean to imply that it would make any where near 100 ft/lb of running torque, preload. As I'm sure you know it takes much more than 15 in/lb of torque on the pinion nut to to make 15 in/lb of running torque, preload.

cus23.jpg
 
Ok, that makes more sense.
As far as the pinion nut torque goes I have taken the crush sleeves out and installed solid spacers with shims to give me the correct pinion preload.
I hate those crush sleeves and retorquing them always messes with the pinion bearing pre load.
 
saskdiesel said:
Ok, that makes more sense.
As far as the pinion nut torque goes I have taken the crush sleeves out and installed solid spacers with shims to give me the correct pinion preload.
I hate those crush sleeves and retorquing them always messes with the pinion bearing pre load.
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I agree on the solid spacer, that fixes the pinion.

Zuk's take on carrier preload;

>I set the CBPL extra high for kyle (150 ft/lbs) while maintaining the prescribed 7.5 BL. Although 150 ft/lbs on the spanner rings sounds terribly high, it is not and translates into an actual 15 inch/pounds of CARRIER BEARING pre-load which is a desired spec to shoot for.....even for a daily driver.

From;
http://www.gearinstalls.com/kyle.htm
 
Toolsrus....I live in glendale....wanna go wheelin' after Camelback toyota gets my truck back together? You sound like you might just know what your talking about, and you might just get to see the diff blow a third time:) :)
 
Kevin does a great job testing the FJ's limits:bounce: :doh: - of course he wheels an 80:grinpimp:
 
homedad64 said:
33" tires,ome lift,arb bumper,warn 9000,4+plus full skids, and no I'm not quite dumb enough to "wheel" on-road,yes I wheel and it's all desert\rock.....she's in gettin' the third diff. now....dumb comments not needed....a little insite would be nice
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From what I have seen, there haven't been that many problems with the rear diff/elocker. Some, but not a great amount.

I would suggest taking your Toyota somewhere else to get your new Diff/locker replaced under Toyota warranty. The successive failures - 3 in a row, suggests maybe the mechanics installing your diff do not know how to set backlash etc and it could be a mechanic caused failure (the 2nd and 3rd failures).
 
well... I just got the call...It's done....friday night will tell if it's done correctly...I'll keep all informed.....kurt
 
I just changed the diff fluid at 15,000 miles on my 07 FJ . I noticed what seems to be metal shavings on the drain plug. There is no noise or anything else that makes me think there's a proplem . Is there something Toyota puts on it from the factory and anything i should be keeping a eye on. I do wheel the truck but i have a lite foot.
 
LandCruisers4Life said:
From what I have seen, there haven't been that many problems with the rear diff/elocker. Some, but not a great amount.

I would suggest taking your Toyota somewhere else to get your new Diff/locker replaced under Toyota warranty. The successive failures - 3 in a row, suggests maybe the mechanics installing your diff do not know how to set backlash etc and it could be a mechanic caused failure (the 2nd and 3rd failures).
Click to expand...

They replaced the diff assembly on all of them that I have heard of being replaced under warranty?
 
Yoda1 said:
I just changed the diff fluid at 15,000 miles on my 07 FJ . I noticed what seems to be metal shavings on the drain plug. There is no noise or anything else that makes me think there's a proplem . Is there something Toyota puts on it from the factory and anything i should be keeping a eye on. I do wheel the truck but i have a lite foot.
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It's normal to have some filings on the magnet from the gears breaking in.
 
the drain plug is a magnet...shavings normal...but...everyone.... this blown diff (three times) never left me stranded...the rear was making noise I blamed on new tires and lift...tire guy told me to get the rear checked...the second time I had a squeek I blamed on brakes or some sand...diff. again....the last time I had a slight noise under hard throttle only...it got worse with speed...entering a hwy was scarry.....I would guess some of you have the same trouble and don't know it yet.....rear noise..get it checked...didn't cost me a penny yet...Kurt
 
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