Catastrophic Knuckle Failure

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brettwilm

brettwilm

SILVER Star
10 Year
Joined
Sep 4, 2014
Threads
12
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204
Location
Tucson
Thank God this happened in front of my house. Hard left U-turn into my driveway and heard/felt clunk and steering loose. Pictured is what I've got. It looks to me like I've lost my four stud assemblies that attach the knuckle arms to my passenger side steering knuckle. In next post I've pictured what I found in the street which I reckon was the last bolt which sheared off.

Likely damage in addition to replacing the lost stud assemblies? I've never serviced my knuckle joints / birfields so I'm in over my head right now. I do recognize that right-front of truck is likely unstable as hell and unsafe to get under.

Thanks for your thoughts.

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Glad you are OK. The knuckle studs were NOT torqued to spec and worked themselves loose. A mud search will reveal its not the first incident of this happening. Usually, it wasn't put back together correctly at some point, causing the failure.

Find a donor knuckle with good studs and another steering arm. Now is a good time for a complete front knuckle rebuild.
 
Improperly seated studs will back out even if the nuts are properly torqued. This is more apt to happen to the right side of left-hand drive vehicles and the left side of right-hand drive vehicles due to the push-pull of the drag link and tie rod on opposite sides of the same steering arm.
 
check yer nuts!
 
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So...trying not to overthink this, would the roadside repair here be to jack up and secure the truck, push the wheel back onto the knuckle, line everything up and install four new knuckle stud assemblies? Hoping to keep things simple at least until I can get this into a garage.
 
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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).
 
brettwilm said:
So...trying not to overthink this, would the roadside repair here be to jack up and secure the truck, push the wheel back onto the knuckle, line everything up and install four new bolts/studs? Hoping to keep things simple at least until I can get this into a garage.
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Yes. Try not to roll the truck before doing this, as you may compromise the axle / birfield inside as well.

Need to remove the sheared studs that are in the bottom of the knuckle ball. They are most likely finger tight if that. The top side of the threaded hole is open into the ball and you can reach the top side of the stud from the interior of the ball.

Clean it well, run a tap through the threads to make sure they are clear, purchase and install new studs, cones, washers, and nuts. Only buy from Toyota. I used red locktite on mine and toqued to 43 lb-ft, but I have been seriously flamed for doing both. Mine have not loosened even a bit in 42K miles.

This is definitely the time for a front axle rebuild because you're going to have to get in there now., at least on this side.
 
BILT4ME said:
<snip> I used red locktite on mine and toqued to 43 lb-ft, but I have been seriously flamed for doing both. <snip>
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This is where we get into a grey area that Toyota does not clearly define.

There is a published torque value of 71 lb-ft for the steering arm-to-knuckle side nut but no mention of stud-to-knuckle torque or the use of a locking compound.

Typically Toyota will pre-coat specific fasteners if they have determined a locking compound is necessary. Driveshaft bolts and nuts are one example that comes to mind. Knuckle studs are not pre-coated.

The "standard bolt torque specifications" chart describes stud bolts in a hardness of 4T and 6T however torque values listed refer only to "hexagon head bolts and "hexagon flange bolts". Stud bolts are not called out.

The standard torque value for a 4T 12mm hex head bolt is 35 lb-ft and a 6T 12mm hex bolt is 53 lb-ft. The shoulder of a stud bolt is obviously significantly smaller than a bolt head and logic would suggest the value should be reduced but I have no idea by how much.

In view of the job the stud does I imagine it is a 6T. I have always tried to get them somewhere around 45 lb-ft and I have not used a locking compound. I have not had studs loosen on me using this procedure but, as always, YMMV.
 
After doing some reading, I'm wondering whether my knuckle studs all sheared or maybe the first three just backed out and the last one sheared?
 
You are very very lucky.

Same thing happened to me a couple weeks back on hwy at speed. Totally lost all steering input with passenger steering are just hanging. No idea how I got the rig to the shoulder and out of traffic.

My top trunnnion race.was cracked and 1 roller.in the bearing broke as well. I highly recomend you replace your top race and bearing as that is the weak link.

I also deformed the bell on the axle housing. Yours is likely ok as not much speed was involved.

So in my case new axle housing (thanks beno), knuckle rebuild with extra strength studs, and while the pumpkin was out did a 5.29 regear.
 
brettwilm said:
After doing some reading, I'm wondering whether my knuckle studs all sheared or maybe the first three just backed out and the last one sheared?
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I caught mine JUST before catastrophic failure.

My PO had hit a guardrail in its history and when I bought the truck, one stud was sheared off. I drove it, as I did not notice any issues until one day when I was washing the truck and happened to glance down and saw that there was only (1) bolt in there when there used to be at least (3). I reached under it to find the last one was part way backed out and I finger-tightened as much as I could and I limped home 14 miles at 15 MPH on back roads.

I put in all new studs and nuts at that time to get me by, then bought a complete replacement set so when I did the front rebuild I would again have all (8) new studs and nuts.

I replaced all when I did my front rebuild (as well as new wheel bearings, trunnion bearings, new axle shaft assemblies (RCV) and new seals, rotors, calipers, and brake pads.) I chose to torque them in and did what I did based on MY life experience of other equipment (farm and other brand 4x4) since I could not find specific information on how to install the studs. Typically, a stud has a fixed depth or a shoulder to stop on when installing. These have neither. I realize I ran a risk of stripping / damaging threads by torquing them in, so I did a few test-fits to see if it appeared to damage threads or anything similar. I chose the 43 LB-FT based on SOMETHING I saw, but I don;t recall what or where it was. I did read almost the ENTIRE FSM before I came to that conclusion.

I also chose to use red Loctite because as I would tighten the studs, there was a chance that the stud could turn as well and loosen. I realize that thee are down-sides to this, as in MUST use heat to remove (250°F+).

I'm glad you did not get injured or injure anyone else, as when the steering arm comes off, ALL steering ability is lost, as the main arm controls the right wheel, and it uses that action through the tie rod to control the left wheel. When that comes off, BOTH arms flop and ALL control is lost.

The Chevrolet version has the main steering arm directly connected to the LF wheel and the RF wheel is controlled by a tie rod on a separate arm, cast into the knuckle. Even if the tie rod falls off, there is at least control of ONE wheel. If the steering arm breaks, BOTH wheels travel the same direction. On the Toyota, they will point out, opposite each other and will likely put it into a spin or rollover if done at speed.

That's my $.03 worth......
 
riffman12 said:
holy hell, glad you're ok.

Guess I should probably get a torque wrench out and go check mine. How common is this issue?
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Common in cases where the steering arm has been removed at some point prior and not properly reattached.
 
riffman12 said:
holy hell, glad you're ok.

Guess I should probably get a torque wrench out and go check mine. How common is this issue?
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VERY.
 
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