Truetrac failure

[Jeffy56]

I'm trying to figure out how spinning tires and hitting dry pavement would break one? Shouldn't it be designed to handle that?

I have 4000 miles on mine after a self-install and no problems as of yet and I've beat it pretty good after the customary 500 mile ring and pinion break in period.

Dry pavement failure would be high speed wheel spin different between sides. Suddenly hit pavement, or rock. TRACTION! The spinning wheel now gripping sends a shock thru the axle shaft. The LS, trying to prevent wheel spin is now hit with that change.

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[AlgUSF]

Dry pavement failure would be high speed wheel spin different between sides. Suddenly hit pavement, or rock. TRACTION! The spinning wheel now gripping sends a shock thru the axle shaft. The LS, trying to prevent wheel spin is now hit with that change.

You wouldn't break a u-joint first?

 

[Jeffy56]

You wouldn't break a u-joint first?

The first stress is at the L Slip. It could travel, but the issue is between the L & R wheel spin difference.

 

[azwjowner]

From Enton
"
What kind of break-in is required with the Detroit Truetrac?
Answer
While Truetrac units do not require a break-in for operation, the gears do “lap” together. While the time required to fully lap the gears will vary depending on driving style and loads, the units will operate smoother with age.
"
So it would seem that whether the break-in procedure was right or wrong for the ring and pinion it shouldn't have had a baring on the truetrac failure.

The Truetrac itself doesn't require a break in. But your installer has to measure the backlash of your ring and pinion (to the thousandth of an inch) prior to replacing your differential carrier with the Truetrac. Then he has to shim the Truetrac to match that existing backlash to the thousandth of an inch, and add shims to either side to set an appropriate preload on the carrier bearings. Hopefully the installer also pressed new carrier bearings into the Truetrac rather than swapping them over.

If everything is done perfectly, yes, your gears don't really notice the difference. But if it's even slightly off now you have a different wear pattern on your gearset. If it's very close, you might be ok and it'll break in. If it's off to any significant degree, you mess up the gears.

 

[azwjowner]

I'm with you; it's unusual for a truetrac to fail.

I understand the general principle behind truetracs, but does that hold true for the versions that are preloaded? The 912A585 (the one for the m186/dana 30 axles) is supposedly* spring preloaded to ~100lb/ft. Would that mean there is a central spring (or springs) and something not quite as robust as a bunch of helical gears? Genuinely curious because this is out of my area of knowledge.

I also wonder if the shop knows it is preloaded. Perhaps they saw that it wasn't freewheeling and said "See that, the truetrac failed"?

* With a quick search, I was able to find several forum posts saying this but nothing from Eaton.

The preload is accomplished by Belleville spring washers that press on the gears. This is, as you might imagine, incredibly robust. You could in theory open up the Truetrac and remove the washers to remove the preload, actually, which I suspect is there to improve the predictability of front steering characteristics in low traction conditions on road.

So no, I would think the front Truetrac is every bit as robust as the rest of them.

 

[grimmjeeper]

You wouldn't break a u-joint first?

Different things can and do break with sudden shock loads like that. You can even break multiple things at once. U-joints tend to be the weak link but not always.

 

[The Last Cowboy]

I'm trying to figure out how spinning tires and hitting dry pavement would break one? Shouldn't it be designed to handle that?

I have 4000 miles on mine after a self-install and no problems as of yet and I've beat it pretty good after the customary 500 mile ring and pinion break in period.

Tires spinning easily on snow or ice, once one hits a dry spot and the tire gets sudden traction at a high RPM. The shock will find the weakest point and something will give. Been there, done that.

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