Aluminum parts on 2018 Rubicon JL

Headbarcode

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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.
Oh, I'm not at all arguing the merits of the strength vs weight of aluminum knuckles. The pic of the shattered knuckle above is the 1st one I've seen. The more common failure is from a loose ball joint wallowing out the tapered holes. A simple steel insert could prevent that, as aluminum itself is softer.

If shape and structural integrity are optimized in a products design, aluminum will have the same strength as steel but at half the weight. Steel shines when it comes to its resistance to warping and being scratched or dented. Steel stands up better to extreme temperatures, whereas aluminum gets stronger in colder environments but higher temps can make it more susceptible to damage.

Personally, I'm a huge fan of aluminum in things like steering linkages, control arms, bumpers, and belly pans. Also worth noting, is I'm coming from the mindset of 4" lift and 40's and the beef to properly support them with a certain amount of overkill.

 

DanW

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Oh, I'm not at all arguing the merits of the strength vs weight of aluminum knuckles. The pic of the shattered knuckle above is the 1st one I've seen. The more common failure is from a loose ball joint wallowing out the tapered holes. A simple steel insert could prevent that, as aluminum itself is softer.

If shape and structural integrity are optimized in a products design, aluminum will have the same strength as steel but at half the weight. Steel shines when it comes to its resistance to warping and being scratched or dented. Steel stands up better to extreme temperatures, whereas aluminum gets stronger in colder environments but higher temps can make it more susceptible to damage.

Personally, I'm a huge fan of aluminum in things like steering linkages, control arms, bumpers, and belly pans. Also worth noting, is I'm coming from the mindset of 4" lift and 40's and the beef to properly support them with a certain amount of overkill.
The great thing about the Jeep parts industry is that if some problem does rear its head, the vendors usually respond very quickly, if not already having something on the market. I wouldn't be surprised to see someone come up with a steel sleeve for those holes.
 

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The great thing about the Jeep parts industry is that if some problem does rear its head, the vendors usually respond very quickly, if not already having something on the market. I wouldn't be surprised to see someone come up with a steel sleeve for those holes.
Only 10k on these knuckles and you can already see them egg shaping on the top and compressing on the btm in the castle nut area. This set had the ball joint castle nut retorq 3 times in those 10k miles.

2019 JLR , 37', 3.5 lift, 3.5"bs rims.

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I personally believe that U.S. Americans are unable to do so because, uh, some, uh, people out there in our nation don't have maps and, uh, I believe that our education like such as in South Africa and, uh, the Iraq, everywhere like such as, and, I believe that they should, our education over here in the U.S. should help the U.S., uh, or, uh, should help South Africa and should help the Iraq and the Asian countries, so we will be able to build up our future. For our children.
You win the Miss America title!
 

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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.
I'll take another look, but I believe our aluminum knuckles are forged, and I'd bet they aren't anything like 1050 or 5005 alloy. More likely a 6000 series, as opposed to something like a 2000 or 7000 series, which is more costly. Auto makers are cheap. 6000 series is cheap, strong, good corrosion resistance, ok fatique properties.

My thought is that if you're going to use aluminum in a steering knuckle, make the contact areas for the tapers larger, as well as the balljoint holes or just bush them with inserts.
 

roaniecowpony

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The JL reminds me of the "weight savings program" we'd seem to do after a new plane design. Once the first plane is made, it typically comes in over the predicted design weight. Then we'd start lightening things or getting rid of them altogether. Same process on every new airplane program. There was a torque tube that had arms on it that went from the captain's side to the first officer's side rudder pedals. The weight saving program changed it to magnesium. Many years later, they were failing and were replaced with aluminum (heavier than mag). :) There are many more stories like that. We lightened them initially, then when in service, we'd begin to beef up things when failures started showing up, resulting in the weight of an airplane (fleet) continuing to increase over its life.

JL owners are changing out aluminum parts with cast iron or adding a lot of steel skids, etc.. 🤔

 
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