Front Diff Tweaked

[MightyM]

I have JLU Sport with a stock open front diff. While in 4 Hi I clipped the edge of a waist high boulder with my driver side front wheel going 15-20 mph. It was a violent impact that resulted in a bent lower ball joint, egged out corresponding hole in the knuckle, and a bent lower control arm. All of these components have now been replaced.

Now, while driving in 2 Hi, there is a speed dependent thrumming. When in 4 Hi there is no thrumming. With the front end jacked up and in 2 Hi, approximately 1/3 of the driver side wheel rotation results in enough friction to turn the front driveshaft. This can be overcome by holding the front driveshaft from rotating but you can really feel the extra friction during that 1/3 of wheel rotation. If I rotate the driveshaft by hand with the driver side wheel held still, the passenger side axle stub rotates freely. This indicates that all is well with the FAD.

There is no crunchiness while rotating the drivers side wheel through the "sticky" zone so I don't believe there are any large pieces of metal floating around in the diff. Since the noise goes away in 4wd, I assume the pinion and ring gear are ok. The spline on the axle shaft looked fine when I had it out to replace the knuckle. That leaves the side and spider gears (and their bearings) in question. Would a bent tooth cause this periodic binding? A damaged bearing? I haven't had a chance to open the diff and take a look. Any guesses on what the cause might be?

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[chevymitchell]

I have JLU Sport with a stock open front diff. While in 4 Hi I clipped the edge of a waist high boulder with my driver side front wheel going 15-20 mph. It was a violent impact that resulted in a bent lower ball joint, egged out corresponding hole in the knuckle, and a bent lower control arm. All of these components have now been replaced.

Now, while driving in 2 Hi, there is a speed dependent thrumming. When in 4 Hi there is no thrumming. With the front end jacked up and in 2 Hi, approximately 1/3 of the driver side wheel rotation results in enough friction to turn the front driveshaft. This can be overcome by holding the front driveshaft from rotating but you can really feel the extra friction during that 1/3 of wheel rotation. If I rotate the driveshaft by hand with the driver side wheel held still, the passenger side axle stub rotates freely. This indicates that all is well with the FAD.

There is no crunchiness while rotating the drivers side wheel through the "sticky" zone so I don't believe there are any large pieces of metal floating around in the diff. Since the noise goes away in 4wd, I assume the pinion and ring gear are ok. The spline on the axle shaft looked fine when I had it out to replace the knuckle. That leaves the side and spider gears (and their bearings) in question. Would a bent tooth cause this periodic binding? A damaged bearing? I haven't had a chance to open the diff and take a look. Any guesses on what the cause might be?

If you hit it that hard, the axle tube is likely bent.

I would un-populate the axle assembly and inspect all of the parts. (Check uni-bearing for binding.)

Once completely empty, run a broomstick or equivalent through the axle assembly and see if it's still straight. You'll likely be able to tell with your naked eye without the dowel.

If the tube is bent, then the shaft alignment will be off and more of an elliptical. The friction you're feeling could be the inner shaft on the inside trying to do an ellipse inside the spider gear because the center of the uni-bearing and knuckle assembly are off by a tiny bit.

Moral of the story: Check for a bent axle tube, inspect uni-bearing and associated parts.

 

[Rodeoflyer]

You know, I've done that and the lower control arm just taco'd thank goodness. I was actually turning left at low speed and hit a 3ft high rock driver side. Taco'd the lower control so I guess it took the brunt but I also have a Rubicon so the axle survived. Sounds like you caught it at a perfect angle to seriously mess the front axle up or at the least bend your CA's badly.

Egged out a hole in the knuckle???

did they replace the front driveshaft?

 

[Rodeoflyer]

If you hit it that hard, the axle tube is likely bent.

I would un-populate the axle assembly and inspect all of the parts. (Check uni-bearing for binding.)

Once completely empty, run a broomstick or equivalent through the axle assembly and see if it's still straight. You'll likely be able to tell with your naked eye without the dowel.

If the tube is bent, then the shaft alignment will be off and more of an elliptical. The friction you're feeling could be the inner shaft on the side trying to do an ellipse inside the spider gear because the center of the uni-bearing and knuckle assembly are off by a tiny bit.

Moral of the story: Check for a bent axle tube, inspect uni-bearing and associated parts.

So he could have actually bent an axle or the tube?? ugh.. that's pretty bad news.

 

[mwilk012]

Bent axles aren’t so bad. Bent tubes are. You’ll need 4 jack stands or a lift, and an alignment.

 

[Rodeoflyer]

Bent axles aren’t so bad. Bent tubes are. You’ll need 4 jack stands or a lift, and an alignment.

True... I'd much rather pay to replace a bent axle. Key words in chevemitchells post 'off by a tiny bit' the difference in smacking something at 5mph (like I did) vs 15-20mph

 

[MightyM]

You know, I've done that and the lower control arm just taco'd thank goodness. I was actually turning left at low speed and hit a 3ft high rock driver side. Taco'd the lower control so I guess it took the brunt but I also have a Rubicon so the axle survived. Sounds like you caught it at a perfect angle to seriously mess the front axle up or at the least bend your CA's badly.

Egged out a hole in the knuckle???

did they replace the front driveshaft?

The tapered hole in the knuckle that the ball seats into is no longer round, now egg shaped.
"They" is me. My local dealer is a piece of crap, and I'm trying not to loose too much $ paying for labor at an independent shop.

 

[Rodeoflyer]

Yep the destruction is pretty much your fault and you have to fix it so there's literally no taking it to a dealer. I've smacked mine around enough that if I take it to the dealer they will document it and likely refuse any future warranty claims so its just cheaper to find a good local mechanic.

So it was enough of force to wallow the aluminum knuckle/ball joint.. wow pretty good smack.

 

[MightyM]

Damage

 

[Rodeoflyer]

Thats what my lower CA looked like but I'm not experiencing the issues you have. I swapped out to rock jock/johnny joint control arms all around but yeah crazy. Taco'd my drive side control arm just like that but haven't had any issues like vibration etc since.

I see you had aftermarket uppers though.. that's interesting. Both my stock upper and lowers bent.

You had some aftermarket upper CA's? Looks like metalcloak uppers.

 

[kah.mun.rah]

Sounds like the solution is an aftermarket D44. ?

 

[Rodeoflyer]

Yep the destruction is pretty much your fault and you have to fix it so there's literally no taking it to a dealer. I've smacked mine around enough that if I take it to the dealer they will document it and likely refuse any future warranty claims so its just cheaper to find a good local mechanic.

So it was enough of force to wallow the aluminum knuckle/ball joint.. wow pretty good smack.

Sounds like the solution is an aftermarket D44. ?

Not just yet haha

 

[chevymitchell]

So he could have actually bent an axle or the tube?? ugh.. that's pretty bad news.

Absolutely. The tube can bend from an impact like what he described rather easily. The bent ball joint is a tell tale. Could be other components, too, so they need inspected, as well.

 

[Rodeoflyer]

Absolutely.. it's going to take throwing some money and really good honest, west coast tech.

good luck with that...

 

[chevymitchell]

Damage

Ah, yes, the control arm taco. Lol.

We had a Jeep fall off an obstacle in Moab and do this, as well. Replaced the arm and drove back to NC. The arm looks bad, but isn’t that bad. I’m more concerned on where all the energy went from bending the ball joint.

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