Nice job!!

so wait.. the illustration from the Service Manual states "37ftlbs". But I'm hearing torque it to 59ftlbs?

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My theory all along here is that the bolt with washer has a different acting friction diameter than the flanged bolts. Smaller head = lower torque for the same clamping force. I don't think the black bolts are coated with something magical that changes their coefficient of friction - to the contrary, I think they are specifically not coated with any friction reducing compounds, unlike the other 'color' bolts where Toyota was tweaking coatings to tweak preload in later years.

Toyota likes the flange bolts because they are cheaper, but they couldn't use them with the dust protector due to the torque that would be applied to the in-molded metal sleeve in the protector. They went to a bolt with washer and adjusted the installation torque for a (near) matched preload.

Anybody that thinks Toyota doesn't know these things and FULLY design/engineer stuff like this is deluding themselves. (I now work at a small US division of Yamaha - I see the same Kaizen stuff that Toyota pioneered many years ago)

I have the ARP bolts waiting for install in my garage - this data puts my mind at ease and I will feel quite comfortable installing them. I did overtorque at least some of the LBJ bolts during install years ago (read the nut spec, used it on the bolts!), so it is worth the piece of mind.

-Charlie

37 ft.lbs = bolts with loose washer, 59 ft.lbs = bolts with flange head.

-Charlie

LBJ Bolts (4 per side) 90080-10066 (96-00)(59 ft/lb)(flanged bolt not for use with dust protector boot) or 90119-10933(01-02)(37 ft/lb)(bolt w/washer for use with or without dust protector boot)

That may be part of the story, but not all. The contact diameter on the ARP washer is 16.2 mm, and the one on Black bolt is 14.8 mm. That's only a 10% difference. Plug that it into the full torque vs preload equation (not the mickey mouse simplified online calculator), and the difference in preload at a given torque is about 4-5%. So that won't explain why the Black bolt generates almost twice the preload of the ARP bolt.

We won't know for sure without an FTIR machine. But the data suggests that there is some kind of a friction reducing coating on the Black bolt. I don't think I stated that it is magical, just that it is good.

I certainly did not mean to imply (and don't think I did) that I know more than Toyota does. In fact I am sure they did their engineering right, and designed the bolts (and torque specs) accordingly. My comment about "reverse engineering" was simply that since Toyota has not publicly shared their calculations with us (at least to my knowledge), we have to make some assumptions as to what they did and why. If you read these forums, you'll see how often people guess as to whether they should use 37 ft-lbs or 59 ft-lbs to torque these bolts, with all sorts of speculative answers. I think this data is helpful in figuring out the right answers with facts, instead of speculation.

Oh, no - you are definitely on the right side here! I'm talking about the people avoiding the 'black' bolts because they are 'weaker' or similar such nonsense. This information is amazing and helpful.

-Charlie

Gotcha, thanks for the clarification Charlie! BTW, I bet you can safely take those ARP bolts up to 70 or even 80 ft-lbs. We'll know more after the next round of breaking things .

But why would you if ARP says 54 # ft?

If <60# generates over 7K of preload then more isn't necessary better... Amirite?

Personally I would rather put less stress on the fasteners than more, and use loctite for good measure

I ordered a set of black bolts for when I retire my current ARP bolts since the 663-1004 (35mm) ARP bolts are just about double the price of the 30mm 663-1003, and I'd like to use the washers

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Well the ARP torque number means nothing without a specific application in mind, because they don't know how much preload you need, so they can't tell you how much torque you should apply. All they can tell you is the maximum torque they feel is safe to apply, which at 54 ft-lbs is about half of what this bolt can handle. But I'm sure they want to be conservative. Or, thinking about @JohnMc 's question earlier, perhaps they specify that torque assuming their lube is applied? I don't know the answer, but that would be a whole different ballgame.

More is better (to a point) when it comes to preload, unless you get close to breaking things. Think of a preloaded bolt as a rubber band to hold two things together - you want a tightly stretched rubber band rather than a loose one. And I'm not sure that 7K is what you want to shoot for, especially if wheeling - I'd shoot for closer to 9K to 10K, given the Black bolt test results.

A high static preload is actually much better than a low one, as it reduces the stress variation in the bolt under external loading. A lower preload causes higher stress fluctuation, and a higher risk of gapping, which is really bad.

That seems like the winning combo to me as well. I'm trying to withhold final judgement until the destructive testing, on the off chance that the ARP bolts are much stronger than the Black ones.

Just sent you a donation via your site. Nice work on this and thanks for taking the time to do it.

Thank you Matt! The support from you guys for this project makes it all worthwhile!

@Spiker Engineering

First of all, thank you for this amazing work!!!

Newbie question: is there any potential down side to using a super strong bolt and a higher torque spec? I guess the heart of my question is this: how strong are the threads on the knuckle, and is there any danger of the knuckle threads becoming a weak point that leads to the very failure that a using stronger bolt was meant to avoid? Honest question. I have no clue. Thanks in advance!!

@cl4Rk , that's a good question. There are some potential risks to using very high strength bolts with relatively weak female threads. But the 4Runner knuckle is made from forged steel, far from a soft material, so the bolt will fail well before the knuckle will (my testing to date has confirmed this, all bolts failed in tension rather than stripping of threads, except for the ARP bolt which only had a two thread engagement).

I also want to be very clear that I am not recommending using a higher preload than what Toyota recommends. I'm only determining what torque should be used for each bolt type to get to that preload. So if Toyota designed the knuckle threads to handle 10,000 lbs (based on our results), then it doesn't matter if you get to that 10,000 lbs by using a Black bolt torqued to 37 ft-lbs or a Red bolt torqued to 59 ft-lbs - the knuckle will still see the same 10,000 lbs, and there is no increased risk of damaging the threads.

There is one other valid concern with very high strength bolts, which is embrittlement. Once you get to 12.9 or higher strength bolts, that becomes a valid concern. That is one of my hesitations with the ARP bolt – if it is indeed a Class 12.9 bolt, then it has a higher risk of failure due to embrittlement. Personally, as of now, it looks to me like the Black bolt has the best of all worlds – very low friction, very low degradation with use, and the needed strength without risking embrittlement. Not clear what the ARP bolt would add to this, other than more risk.

This is where the failure numbers will come in handy. For most people I agree that not exceeding OEM preload is perfect. For those that wheel hard they might need to increase that preload. Every single LBJ bolt that I failed was due to shear. Repeatedly hitting big rocks with big tires causes stress that Toyota never designed the system for. That repetition eventually causes the bolts to shear in plane with the LBJ/Spindle. By increasing preload as close to the forged threads pull strength we can mitigate that. Super rare use case but it will help a lot of folks that wheel stupid shit. lol

Agreed, there's lots of margin to increase preload above what Toyota recommends. Not much of a downside to it, either. And the bolt will fail in tension way before the knuckle threads will yield, provided you have 4 or more threads engaged.

Regarding bolt failures in the field, I've seen a FB post of someone having that happen, but it's not clear how they know it was a shear, rather than tensile, failure. Any chance you have pictures or remnants of failed LBJ bolt joints?

I'm having a bit of a hard time seeing how the joint can fail in shear as long as the bolts are tight. In addition to the friction force, there are two shear cones on the LBJ that should take the shear loads. What happened to these cones to let the bolts fail in shear?

My suspicion is that the bolts start to back out due to the heavy loads you describe, and allow gapping to take place. Once the joint gaps, the impact loads lead to oscillating loads in the bolts, the shear cones are no longer effective, and the bolts do in fact fail either from shear or tension.

That's why I personally think that the most critical thing in the LBJ bolts installation (aside from preloading to the right load, around 10,000 lbs or more) is to ensure the bolts don't back out. And after way too many years in the aerospace industry, I can tell you that loctite is not the best way to ensure that.