Aluminum knuckle failure

[CarbonSteel]

I thought I had looked at them before and they had looked forged to me. So, I looked again this morning. Sure look forged to me. The fidelity of the lettering and foundry timer is too fine to be sand cast and the parting line is wider than I'd observed in permanent mold low pressure casting. My background includes manufacturing engineering with a focus in machining, not forging or casting. But I've seen a lot of both.

Agree; those appear to be a forge lines and not cast. My guess is T6061 heat treated. Also, cast aluminum would not hold up to normal driving stresses much less wheeling.

Sponsored

 

[Nailgun]

68477358AA - Front Knuckle, Right
68477359AA - Front Knuckle, Left

Thanks for the part numbers. ?

I ran them in my online Mopar parts dealer. Pricing is in Canadian. Looking at the fitment, it would suggest that any "wide" trak Gladiator would have the steel knuckles.

68477358AA - Front Knuckle, Right

68477359AA - Front Knuckle, Left

 

[roaniecowpony]

Found this at Front Axle: Housing, Differential and Vent for 2021 Jeep Wrangler | MOPAR Discounted Parts

 

[roaniecowpony]

I went back to see where it broke. I was surprised to see it broke through the middle of the tapered hole for the balljoint. But then I saw the dark surface in the hole. Looks like it might have been loose enough to let dirt into the taper.

 

[Nailgun]

Found this at Front Axle: Housing, Differential and Vent for 2021 Jeep Wrangler | MOPAR Discounted Parts

That looks a little better. I wouldn't be surprised if our pricing is quietly adding in shipping costs.

I went back to see where it broke. I was surprised to see it broke through the middle of the tapered hole for the balljoint. But then I saw the dark surface in the hole. Looks like it might have been loose enough to let dirt into the taper.

Yup....that is super dirty and bent.Wallowed out long before failure.

 

[NewJLU2019]

I may be wrong, but I think the ball joint failed as the Jeep unloaded with the bounce, and that took out the axle and knuckle.

So, ball joint may have been the trigger.

Question I know what the word bouncing means. Are you saying his front end was bouncing because he didn't have locker on and shouldn't be letting his Jeep bounce up and down on axle and he should have stopped and went different way? Trying to learn for myself.

 

[stumblinhorse]

Question I know what the word bouncing means. Are you saying his front end was bouncing because he didn't have locker on and shouldn't be letting his Jeep bounce up and down on axle and he should have stopped and went different way? Trying to learn for myself.

Wheels will hop on hard surfaces when they suddenly loose traction and Spin and grab and hop. Lockers do 2 things in that scenario; first obvious one is more traction on all wheels and keeps you moving, second is stopping wheel spin since they turn at the same RPM, one wheel won’t suddenly spin and hop.

If you drive dirt/gravel roads you have encountered “washboard” sections. This is from a small form of wheel hop. Much less violent, but that is why most washboard is on uphill sections.

hope that helps.

 

[NewJLU2019]

Wheels will hop on hard surfaces when they suddenly loose traction and Spin and grab and hop. Lockers do 2 things in that scenario; first obvious one is more traction on all wheels and keeps you moving, second is stopping wheel spin since they turn at the same RPM, one wheel won’t suddenly spin and hop.

If you drive dirt/gravel roads you have encountered “washboard” sections. This is from a small form of wheel hop. Much less violent, but that is why most washboard is on uphill sections.

hope that helps.

Thanks so, the lockers should have been on at that time.

 

[stumblinhorse]

Thanks so, the lockers should have been on at that time.

Rock crawling, lockers on generally all the time. Because in rock crawling there is a tendency to have a wheel off the ground. Once that happen that axle is providing no force to the ground. Wheel in the air spins…

exception is tight turns. Lockers on on hard surfaces making a turn is hard on components. And can make you miss a line.

 

[Carolina Jeeper]

How can you determine that it’s a part failure and not something that the driver subjected it to that’s outside of its design parameters?

Working as a mechanic for 18 years I'll agree 100% with that valid question. Someone that is unaware or dismissive may disagree.

 

[Spank]

LOL. He sure has a lot of trail badges for a Newbie.

Yeah, this kinda confuses me as well. Dude is new to wheeling, yet is almost out of room on his fender for any more Badge of Honor badges.

 

[JROOO]

"new to offroading"???

 

[gato]

Question I know what the word bouncing means. Are you saying his front end was bouncing because he didn't have locker on and shouldn't be letting his Jeep bounce up and down on axle and he should have stopped and went different way? Trying to learn for myself.

The owner of the Jeep and some here are linking "not using lockers" to the bouncing. Jeeps can bounce/hop with or without lockers. On a U-joint Wrangler, like in this case, with wheels turned, as you spin the wheel looking for traction the power delivery is not smooth because the U-joint angles cause a bind-release-bind-release cycle. That tends to make the front of the Jeep start to hop/bounce up and down.

Bounce/hop is bad for a few reasons. One, when the Jeep is in the air the wheels are spinning, when the Jeep lands the wheel may get sudden traction or wedge on terrain, causing a sudden "chock" (stop or sudden slowdown) to that wheel - those forces then go to axle/U-Joint/gears/etc. Something may break.

Second thing is that when the Jeep unloads and loads it puts stress on the ball joints - literally trying to rip the ball joints or "unpress" them from the axle/knuckle.

Bottom line is, if you are trying to clear an obstacle and your Jeep starts to hop, back off the gas immediately, reposition and try a different line. Nothing good (other than youtube videos) comes out of bouncing/hopping your Jeep





P.S. Those with OEM (anyone with 4-Hi Auto) or aftermarket (e.g. RCV) constant velocity axles (vs the more traditional U-joint) will experience a lot less if any hopping. I don't want to start another debate on U-joint vs CV-joint, but at least as far as hopping goes, the CV causes less of it.

 

[roaniecowpony]

The owner of the Jeep and some here are linking "not using lockers" to the bouncing. Jeeps can bounce/hop with or without lockers. On a U-joint Wrangler, like in this case, with wheels turned, as you spin the wheel looking for traction the power delivery is not smooth because the U-joint angles cause a bind-release-bind-release cycle. That tends to make the front of the Jeep start to hop/bounce up and down.

Bounce/hop is bad for a few reasons. One, when the Jeep is in the air the wheels are spinning, when the Jeep lands the wheel may get sudden traction or wedge on terrain, causing a sudden "chock" (stop or sudden slowdown) to that wheel - those forces then go to axle/U-Joint/gears/etc. Something may break.

Second thing is that when the Jeep unloads and loads it puts stress on the ball joints - literally trying to rip the ball joints or "unpress" them from the axle/knuckle.

Bottom line is, if you are trying to clear an obstacle and your Jeep starts to hop, back off the gas immediately, reposition and try a different line. Nothing good (other than youtube videos) comes out of bouncing/hopping your Jeep


P.S. Those with OEM (anyone with 4-Hi Auto) or aftermarket (e.g. RCV) constant velocity axles (vs the more traditional U-joint) will experience a lot less if any hopping. I don't want to start another debate on U-joint vs CV-joint, but at least as far as hopping goes, the CV causes less of it.

I agree.

When I look further at the pictures from the video, the top balljoint is sheared flush in axle housing yoke. It's possible the bouncing overloaded that upper balljoint and it sheared first and caused the knuckle to fail. I'd lean toward that being more likely.

 

[intentsrig]

Second one I have seen broken. Happened to some guy’s JL on the rubicon last year.

The aluminum is too soft. The top knuckle ball joint holes were wallowing out on mine when I switched to Reid’s.

Sponsored