Catastrophic Knuckle Failure (1 Viewer)

[shocktower]

Knew what this was going to be before I opened the page...

Seems to be all too common lately.

The knuckle and trunion bearings are likely damaged. If you can extract the broken studs,fit 4 new studs and get everything lined back up you might be able to drive it a short distance at low speeds (in an emergency).

You are better off just towing it, and as said by others check your nuts, I don't understand how you never noticed it was loose. Ok you probably trashed the knuckle, and for sure the trunion bearings, I am glad you had this happen at a slow speed in front of your house and not at high speed

 

[shocktower]

That's a debate that has raged for years. My opinion is that stud torque doesn't matter much as the nut torque is transferred throughout the fastener, pulling equally on the nut threads and the knuckle threads. In fact, I'd go so far as to say that you risk messing up the threads on the knuckle side by torquing the stud- what's stopping the stud? Probably the tiny shoulder mashing into the knuckle thread. I believe that the steering arm wasn't seated properly and as it moves around the nuts lose torque and eventually walk out far enough that the movement in the steering arm destroys them. I also believe that using thread locker makes it impossible to check the torque later. If I were going to use it, I'd only use it on the knuckle end of the stud.

On the other hand, many people torque the studs without issue, so there's no clear 'right' answer.

I totally disagree, why would you only torque one, in every application which has studs, you always torque the studs first, I mean common sense, why would you only torque one and not the other

The torque value is typically calculated based on the thread diameter, and if it's a known failure point, the tensile force it usually sees, or is expected to see. So there is not any reason I can think of to reduce the installation torque. You're correct that grabbing this shoulder is a problem, but there's a snubber made for this, even though I've never seen anyone use one. This is why most manufacturers don't use them, unless they can install them on the assembly line. The process is typically to use two nuts, jammed together, and then stake the stud. This reduces the deformation resulting from using two nuts to drive the stud, and prevents (hopefully) the stud from backing out.

I'm surprised Toyota didn't do this. It's typical for SAE and aviation in the US.

The new ones from Toyota have Torx heads one the studs now

 

[concretejungle]

On my last knuckle job, i used blue loc-tite to ensure this wouldn't happen. Knock-on-wood i've never had loose studs before, but i wanted to ensure that stays consistent.

 

[shocktower]

Cleaned off sheared stud end from post #7. I guess this thing is a hero because it was keeping my steering together by itself until it failed. I have the cone washer, flat washer, and nut back on.

I'm told there is supposed to be a fitting on the end of this stud so it can be torqued into the knuckle. I don't see any fitting you can put a wrench on, on the end of this. Does anyone think this is was a hand-tightened hardware store part from PO or am I missing something? Would a mechanic have ground it off?

View attachment 1548563

That is an OEM stud, they have since put torx heads on them now, buy a set of 8 of all the parts needed, and you might need a new knuckle too

 

[BILT4ME]

<snip> I don't understand how you never noticed it was loose. <snip>

When I had this issue with mine (but no catastrophic failure):
I was driving mine at full highway speeds and it drove "normally". What got my attention was as I was taking an exit ramp at 55 MPH and as I turned right, I felt a "delay" between when I turned the steering wheel and the truck actually changed direction. Yet, at low speed, it felt totally normal. I drove it with this issue for probably a month before I actually looked at it and discovered the issue. Part of it was ignorance of how the Toyota steering worked, as I had not yet rebuilt my front axle personally. Now that I have done it, I know first-hand what to watch and feel for.

I'm usually pretty sensitive about all things a vehicle is doing when driving. I am so thoroughly impressed with how the LC drives, handles, does its thing, that what I thought was "normal" looseness and wander compared to other 4x4's I've driven, worked on, and owned, that I didn't feel was out of the norm. It also shows me how stout the Toyotas really are and what they are capable of, even when "broken".

 

[brettwilm]

When I had this issue with mine (but no catastrophic failure):
I was driving mine at full highway speeds and it drove "normally". What got my attention was as I was taking an exit ramp at 55 MPH and as I turned right, I felt a "delay" between when I turned the steering wheel and the truck actually changed direction. Yet, at low speed, it felt totally normal. I drove it with this issue for probably a month before I actually looked at it and discovered the issue. Part of it was ignorance of how the Toyota steering worked, as I had not yet rebuilt my front axle personally. Now that I have done it, I know first-hand what to watch and feel for.

I'm usually pretty sensitive about all things a vehicle is doing when driving. I am so thoroughly impressed with how the LC drives, handles, does its thing, that what I thought was "normal" looseness and wander compared to other 4x4's I've driven, worked on, and owned, that I didn't feel was out of the norm. It also shows me how stout the Toyotas really are and what they are capable of, even when "broken".

There was no degradation to my steering until the last stud sheared. And since the other three studs probably just worked loose and dropped out, I never heard them.

 

[-Spike-]

I totally disagree, why would you only torque one, in every application which has studs, you always torque the studs first, I mean common sense, why would you only torque one and not the other

And there's the debate, raging for years, alongside the one about Loctite.

As for common sense, I can try to explain but I doubt I will convert you. Bottom line, I haven't heard of anyone trashing threads by torquing the studs, so the argument is pretty much moot anyway. Also, let's be clear, I'm not saying you should leave them loose, all I'm saying is that the nut torque and the assembly being fully seated is more important.

So for the common sense- what holds the nut on? Tension. If this was a bolt, the tension on the threads in the knuckle would be holding it in. Studs are bolts with a removable head. Torque applied to the nut is applied to the stud. If it's good enough for the nut, it's good enough for the stud. It's the same assembly. When you torque the nut, you are in fact torquing the stud.

So why use studs? Here's an explanation I pilfered from a Google search- Studs provide the ability to obtain much more accurate torque values because the studs don't twist during tightening as do bolts. Because the studs remain stationary during nut tightening, the studs stretch in one axis alone, providing much more even and accurate clamping forces.

So what looks like 'common sense' is more of a 'common misunderstanding'.

And just for fun (and because I foresee a discussion on lock washers coming) here's an article on fasteners.

 

[Dave 2000]

I am in the 'use thread lock' camp and based my decision on studs I have seen working loose (not my car), and that grease and possibly oil working it's way down the thread, perhaps aggravating the problem?

@BILT4ME sod the flamers, use whatever works for you mate.

Regards

Dave

 

[itbrokeagain]

I check mine every wheeling trip and every once in a while I have a loose one. I also have front found hub nuts, rear axle shaft nuts, front third member nuts all loose. I check all on a regular basis.

 

[bajaphile]

Just thinking out loud...

With a bolt, the torque applied by turning the bolt turns into an axial preload, which is then related to the clamping force.

With a stud, you install it, then what is attributing to its torque value (besides the friction of the threads)? If it's a thru hole, it will just keep going through of course. If it is a blind hole, the stud will bottom out. If you apply torque to that bottomed out hole, the stresses will be transferred into the threads, with thread damage possible.

What I am saying is that torque on a stud is irrelevant. (AKA torquing a stud to a certain value). From what I've found, a stud should be installed essentially finger tight, then turned 45° (estimate). In this specific application, a compound should be used to hold the stud in place due to vibration. The clamping force is obviously then created by the nut applying an axial force to the stud.

Just my take on it. I'm an ME, but do not specialize or deal with many fasteners...MIL-HDBK-60 and internal specs do not go over stud torques for installation into the part, only with nut torque. The values are equal to that of a bolt otherwise (based on things like axial strength of material, diameter, material processing and weather or not it is a lubricated or dry install).

 

[BILT4ME]

Where the the NASA Engineers when we NEED them damnit!?!?!?!?!?

Don't they KNOW this is rocket science?

 

[bajaphile]

LOL seriously. I am generally interested in what others opinions are though. Interesting topic.

 

[mudgudgeon]

Last knuckle rebuild I did, I replaced the studs and hardware. I tightened them in until the shoulder bottomed out on the knuckle using the double nut method. Couldn't find a torque value, so I used the Armstrong method. (Tighten by feel)

From what I have observed, undoing the nuts to remove the steering arm has a possibility of backing out the stud somewhat before the nuts let go. You are then left with a stud in an unknown state without knowing if it has any residual tension on the stud threads in the knuckle.

I think (my opinion, and I'm happy enough to be wrong) torquing the stud is useful to resist loosening when you undo nuts later for maintenance. I think the same is true with hub/drive flange studs.

 

[mudgudgeon]

Where the the NASA Engineers when we NEED them damnit!?!?!?!?!?

Don't they KNOW this is rocket science?

Oh, come on! Everyone knows this isn't rocket science! It's rocket surgery.

 

[Dave 2000]

Given we are clamping two components together, and that they are subjected to considerable forces which include rotational, compression and an element of heating and cooling, torqueing and using thread lock on the threads is a no brainer for me.

It would not be a bold statement to say my 80 gets more regular off road use than most I come across, out most weekends and I live up a track that is as rough as a bears arse, IIRC I did my knuckles about 6 years ago and zero issues.

I would add, my 80 is stock when it comes to suspension and wheel/tyre sizes, perhaps some of the various mods to suspension and running gear are creating the problem by adding additional load/stress? It is IMO not a common problem on typical road going 80's soooooo?

Regards

Dave

 

[concretejungle]

To further my Loc-tite post, i truly believe that torque is important, but as stated before, eventually there is a chance that grease and gear oil can seep down the studs and loosen them. I believe that.

So i pulled mine apart and cleaned them in the parts washer, then sand blasted them to like new. I used air and brake cleaner to ensure the knuckle threads were perfectly clean and dry. Then i replaced with new studs with blue loc-tite. After torquing them down, i let them sit 24 hours just to ensure the loc-tite had time to dry. Then i added the grease and finished the job.

Knock-on-wood, my studs have never come loose with this technique. Not even a little.

 

[Rifleman]

I helped a buddy of mine do his axle rebuild about a year ago. I told him about all the problems I've read about with these nuts coming lose. So i told him he should check the torque on his nuts, just to be sure they were still tight. He said why, we painted witness marks on them when we did the job, and the marks were still lined up, so they should still be tight. Anyway he finely agreed with me to check them, 2 out of the 8 were lose, not much, only a few foot pounds, but they were still lose. So now he's going to make it a regular practice to check the torque on those nuts every time he changes his oil. I think that would be a good habit for all of us to get into.

 

[icorradoi]

To further my Loc-tite post, i truly believe that torque is important, but as stated before, eventually there is a chance that grease and gear oil can seep down the studs and loosen them. I believe that.

So i pulled mine apart and cleaned them in the parts washer, then sand blasted them to like new. I used air and brake cleaner to ensure the knuckle threads were perfectly clean and dry. Then i replaced with new studs with blue loc-tite. After torquing them down, i let them sit 24 hours just to ensure the loc-tite had time to dry. Then i added the grease and finished the job.

Knock-on-wood, my studs have never come loose with this technique. Not even a little.

What torque spec did you torque the studs down to?

 

[concretejungle]

What torque spec did you torque the studs down to?

"extremely tight"

Without having the torque head bolts, i had to double nut them, so getting a real torque spec was nearly impossible.

 

[BILT4ME]

What torque spec did you torque the studs down to?

I went to 43 LB-FT (I think). I got that spec by reading some other stuff (based on stud diameter) or it might have been about where the Torx tip sheared off the stud, so I figured that was tight enough. Then I used the double nut method. I also used Loctite Red, but some prefer blue. Whatever you want.