Aluminum parts on 2018 Rubicon JL

[mgroeger]

I think he’s talking about the track bar/sector shaft brace, but not positive, not sure why I’m even responding………

I know... the only thing more generic could have been "Anyone know how to replace stuff?"

 

[Oakey]

The original premise was that aluminum knuckles on the JL are weak.

They are not, for their intended purpose. Not at all.

Let's imagine Jeep went with steel knuckles on the JL. They would be light duty and would meet the exact same specifications for load and stress that the current aluminum ones meet. Exact same. Just heavier.

If I were going to use my Jeep in a way that I felt required stronger steel aftermarket nuckles, I'd do what some of the guys in this thread have done, especially with anything heavier than a 37" KO2. JK owners had steel knuckles and replaced them for heavily modded Jeeps, same as JL owners.

I don't know the exact spec, but I'd bet some money that the JL knuckles are actually designed with higher load/stress limits than the steel ones on the JK. Nearly every part in the JL drive train is stronger than that of the JK. Again, the rental outfits in Moab will tell you that suspension/axle component failures among their JLs is not nearly what they were with JK's. I'm not calling the JK weak, but rather making the comparison refuting the idea that the JL's components are weak. (For the record, I'd worry about the JK's axle housings long before their steering knuckles.)

So the idea that in OEM stock form they would somehow be stronger in steel is just not true. Of course the aftermarket steel knuckles are significantly stronger than either. These heavily modified Jeeps are SIGNIFICANTLY heavier and with significantly larger/heavier tires/wheels, they must bear much greater loads. So anyone expecting the stock knuckles to hold up to those kinds of stresses and then calling them weak just doesn't understand physics or engineering or economics.

Btw, I see LOTS of JL's in our local Jeep club beating the hell out of them on 37's with totally stock steering components. Nobody's broken a thing yet.

Well here is a pic of what happens to a aluminum knuckle when a ujoint fails! It's quite a bit problem your not limping it off the trail!

 

[sourdough]

Are you sure of what failed first?

 

[mgroeger]

Are you sure of what failed first?

If I had to guess I'd say the U joint let go first. I saw a U joint fail on the trail and the knuckle would have been OK if they would not have moved the Jeep. Once the U joint fails there is a ton of pressure on those two ball joints and all it takes is rolling the Jeep a foot or tow and BAM there goes the knunckle.

 

[Oakey]

If I had to guess I'd say the U joint let go first. I saw a U joint fail on the trail and the knuckle would have been OK if they would not have moved the Jeep. Once the U joint fails there is a ton of pressure on those two ball joints and all it takes is rolling the Jeep a foot or tow and BAM there goes the knunckle.

Thats usually not the way it works when engaged on a trail that causes a ujoint to fail. Most the time you have to move the jeep for stability... The aluminum knuckles just shatter when they do let go and it's alot easier to break them than most realize.

Also we have been seeing alot of wear / compression in the knuckles were the ball joints attach. I was having to retorq my ball joints every 5k miles or so... Thats one of the reason I just went with Reid Iron Knuckles...

 

[DanW]

Well here is a pic of what happens to a aluminum knuckle when a ujoint fails! It's quite a bit problem your not limping it off the trail!

Well, let's see the context. What suspension/wheels/tires was this person running and what were they doing with it?

If even close to stock setup, or mildly modified, it probably involved a Kentuckian and some hill country spirits consumed not too long before the mishap.

 

[OllieChristopher]

Well, let's see the context. What suspension/wheels/tires was this person running and what were they doing with it?

If even close to stock setup, or mildly modified, it probably involved a Kentuckian and some hill country spirits consumed not too long before the mishap.

This is all speculation. Stuff breaks when going off road. I would be nervous doing any serious wheeling with the OEM aluminum knuckles once I went through a ball joint replacement cycle. I'm of the opinion that the factory aluminum knuckles are a consumable part once a a few ball joints are replaced.

Any harder dissimilar metal that is pressed into aluminum wears out the cavity over time. I went through this exact same thing with my KTM PDS suspension. After 2 heim joints were pressed out/in the swing arm hole was beginning to wear. I ended up using an oversized aftermarket one to make up the difference.

So the idea that in OEM stock form they would somehow be stronger in steel is just not true.

The aluminum knuckles are not ever going to be as strong as a steel one. It is the reason that the JT, XR, diesel and 392 models are made of steel.

FWIW, from what I can see visually, the factory steel knuckles are interchangeable with the aluminum ones.

 

[DanW]

This is all speculation. Stuff breaks when going off road. I would be nervous doing any serious wheeling with the OEM aluminum knuckles once I went through a ball joint replacement cycle. I'm of the opinion that the factory aluminum knuckles are a consumable part once a a few ball joints are replaced.

Any harder dissimilar metal that is pressed into aluminum wears out the cavity over time. I went through this exact same thing with my KTM PDS suspension. After 2 heim joints were pressed out/in the swing arm hole was beginning to wear. I ended up using an oversized aftermarket one to make up the difference.



The aluminum knuckles are not ever going to be as strong as a steel one. It is the reason that the JT, XR, diesel and 392 models are made of steel.

FWIW, from what I can see visually, the factory steel knuckles are interchangeable with the aluminum ones.

For their load rating, they are. It isn't about material but rather the loads they are rated to handle. The stock knuckles are light duty, whether aluminum or steel. Even if they were steel, you'd want to get beefier units if you do any heavy modification, particularly with heavy tires/wheels.

I would bet money that the 392 knuckles are rated for higher loads. Otherwise they would not have changed them.

 

[Headbarcode]

For their load rating, they are. It isn't about material but rather the loads they are rated to handle. The stock knuckles are light duty, whether aluminum or steel. Even if they were steel, you'd want to get beefier units if you do any heavy modification, particularly with heavy tires/wheels.

I would bet money that the 392 knuckles are rated for higher loads. Otherwise they would not have changed them.

I saw an install video that included the factory aluminum and Reids knuckles being weighed on a postal scale. The aluminum ones weighed 7lbs vs Reids at 27lbs. The Reids are modeled after the same ones that they've been putting on competition Baja race trucks.

 

[OllieChristopher]

I saw an install video that included the factory aluminum and Reids knuckles being weighed on a postal scale. The aluminum ones weighed 7lbs vs Reids at 27lbs. The Reids are modeled after the same ones that they've been putting on competition Baja race trucks.

It's a lot of difference in weight but piece of mind is worth it.

 

[DanW]

I saw an install video that included the factory aluminum and Reids knuckles being weighed on a postal scale. The aluminum ones weighed 7lbs vs Reids at 27lbs. The Reids are modeled after the same ones that they've been putting on competition Baja race trucks.

And I guarantee they are rated for higher loads than any stock knuckles, including steel.

The whole point in aluminum is light weight and I'll say this again, even though some of the resident metalurgists around here won't believe it. Pound for pound, aluminum is stronger than steel. So a pound of aluminum will have more strength than a pound of steel. The whole point is to get to the desired level of strength with less weight.

But comparing aftermarket steel knuckles or even OEM steel knuckles designed to handle more stress (392) to a stock knuckle that has a lower stress tolerance is not a fair comparison.

If you compared a JK stock steel knuckle with the JL (non-392) aluminum knuckle, I'd bet money the aluminum one is stronger and is designed to handle more stress than the JK.

What is being misunderstood is that I am NOT arguing that the stock JL aluminum knuckle is stronger than either the steel 392 knuckle or an aftermarket knuckle made for larger/heavier tires (as in 37+") That is not at all what I'm saying, so one must read very carefully before drawing that conclusion.

 

[Headbarcode]

It's a lot of difference in weight but piece of mind is worth it.

Especially when the nearest legal offroading is about 4 hours away from home and trailers owned by friends or those who owe you a favor.

Added weight is unavoidable when beefing up to fully support larger tires and lift height. At the same time, certain upgrades help to shed weight to offset overall build weight. For example, the Antirock sway bar kits allowed me to ditch the edisconnect motor and the steel skid plate for it.

 

[OllieChristopher]

The whole point in aluminum is light weight and I'll say this again, even though some of the resident metalurgists around here won't believe it. Pound for pound, aluminum is stronger than steel.

You also have to consider the volume when deciding on use. A chunk of aluminum is going to be close to 2 1/2 times larger in size than the same weight of a ferrous iron material counterpart (titanium being the exception).

It is all dependent on the alloy content. I can assure you that a piece of 1050 or 5005 aluminum is going to be much weaker than the same volume or mass of the weakest irons.

I'm confident that the OEM aluminum knuckles are being used as a way to save weight with a sacrifice in strength. Think aluminum steering box as an example.

Manufacturers are using every weight saving option available due to meet current EPA demands. The aftermarket is filling in the void to offer stronger components for hard use off road.

 

[Oakey]

Well, let's see the context. What suspension/wheels/tires was this person running and what were they doing with it?

If even close to stock setup, or mildly modified, it probably involved a Kentuckian and some hill country spirits consumed not too long before the mishap.

Was a 3 diamond trail. JLUR running 37" with lift and such.

I honestly think your pushing the aluminum knuckle if you run anything more than stock!

Because jeep runs the iron knuckles on their next level lightly modified stock rigs.

 

[DanW]

Was a 3 diamond trail. JLUR running 37" with lift and such.

I honestly think your pushing the aluminum knuckle if you run anything more than stock!

Because jeep runs the iron knuckles on their next level lightly modified stock rigs.

Jeep did that on the 392 because it delivers significantly higher stress loads than the other engines, especially with Selectrac. Selectrac may shock load them more, as it reacts and sends power to the front quickly. That likely causes greater loads than typical with part time 4wd.

Also, rental outfits in Moab are finding their JLs seem to be doing just fine with 35s and 37s. I've not heard any talk from them about weak knuckles yet.

But if you beat on it pretty hard with 37s, it might not be a bad insurance policy. But nobody in the Jeep clubs I'm in has had an issue. Lots of 37s among them.

We'll see as the miles pile up, but they've seen more breakage issues in other components from JKs with 35s than JLs with 37s.