Toyota Carnage

[Slartibartfast]

My dad's '01 Tundra made a generally bad-sounding noise a couple weeks ago while he was trying to unstick it from the eight inches of snow it had managed to get stuck in. (Gotta love open diffs.) I assumed he'd blown up a CV joint. He put it back in 2x and I yanked it free with the Pathfinder. He drove it out to clearer ground, and then we had a look underneath.

 

 

Yeah... that's not a CV joint. That's the pinion.

 

Long story short, it got a new front diff from the wrecking yard, and the old busted diff came home with it. A friend and I took it apart last night to see if we could work out what had gone wrong.

[Slartibartfast]

Hit the post button by mistake... anyway, here's what we found inside.

I didn't expect to see bite marks on the carrier.

 

 

The hell happened here?

 

My dad said the surface of the pinion shaft where it broke looked more like pot metal than proper hardened steel. I haven't broken enough good-quality steel to know the difference. Any metallurgists on here?

 

 

Most of the missing pieces were stuck to the drain plug.

 

My dad said it made a cracking sort of noise a few days previously when he was trying to shift out of 4x, but he just assumed it was the 4x4 disengaging with a bit of torque bind on it. Evidently it wasn't. It sounds like it failed under torque bind, but in a non-lifted rig on stock-sized tires that isn't wheeled, that seems like a weak excuse, especially if this front end was expected to survive in a V8 pickup with a tow hitch. It did have some trouble going into 4x a while back, maybe the actuator ended up stuck in 4x for a while?

Speaking of the actuator, I was amused by how they rigged it up. It's just a servo motor bolted to the passenger's side axle tube that slides an engagement sleeve back and forth. For 2x, it pulls the sleeve one way or the other, decouples the axle to the passenger's front wheel, and the open diff takes care of the rest. I'm not sure if that's clever or idiotic, but either way I prefer locking hubs and a stick through the floor.

 

I figure I'll weld up a "you done broke it" trophy out of the ring and pinion.

[Kingman]

We had a newer Tacoma in the shop with the same issue. It was making awful noises and when I grabbed the LH CV joint it flopped all over the place inside the carrier.

[Precise1]

Certainly not a metallurgist, but a machinist with diverse experience...

There are new alloys being used/developed that defy the old looks like/smells like/feels like metrics, but that doesn't mean they better either. Often they are just cheaper/lighter/etc and should be 'just as good' on paper, or should I say 'in CAD'. Most of the time they work just fine, but...

Some alloys may have the same wear resistance and load psi, but not as good shock resistance or what ever the case may be. Perhaps there is a variance/flaw in the casting/machining process. The part may have been properly engineered and manufactured, but the specs it was based on 'assumed normal load' not 'Kingman tranny drops'.

 

When there are issues with a vehicle, I'd much rather it be a few specific components, regardless which; more easily fixed and more likely to have re-engineered aftermarket parts available. Otherwise you are stuck with something that always has problems and nickels and dimes you to death.

 

That said, it is a surprise failure to me. I'm guessing a manufacturing problem with the part. Once a major gear lets go like that, the damage is going to get crazy and be hard to read...

 

B

[Kingman]

Kingman tranny drops... goes to show how over engineered Nissans used to be.