Debugging a scary moment - steering wheel not in control / broken control arm / WHAT???

[alschnertz]

Wow, what a very unusual breakdown. I cannot imagine a curb impact doing that.
Also can't imagine that bolt ever coming loose or breaking off under normal use.

Did you ever notice any clunking in the front end prior to the incident?
I'm suspicious of what was touched during the alignment in Jan. 2020...
There's really no reason to remove a control arm bolt during an alignment. However, maybe someone loosened it and forgot to tighten it back up?

[cn90]

And from the itemized listing, I can tell the repair would include a complete replacement of control arm and bolts.

This is suspicious bc an alignment job at 50K involves mostly adjustment of the tie rod nuts and that is all.

- Why replaced control arm?

- Why replaced the bolts? Where did the bolts come from, cheap Chinese bolts from Pepboys or Volvo dealer? Were the bolts over-torqued by some young gorillas?

- The aft bolt, IIRC, is M14 and is very strong.

- Another theory is they inserted the vertical bolt and forgot the nut (honest but potentially fatal mistake)...

[oragex]

Even if the large 18mm bolt for the rear bushing was loose, to have it breaking like such in an impact, the wheel would have been very damaged on the outer - possibly from a very strong side-impact. An 18mm bolt in good condition needs a tremendous amount of shear stress to fracture. If this happened, the subframe metal would be very deformed around the holes for the bolt - the holes appear to be free of any deformation. That would have also caused the control arm to break or at least deform at some points

My guess is rather the bolt was over-tightened at some point in the past, causing it to become brittle and to fracture with little impact - if any at all - from road potholes or a cure. The bolt was possible already very close to the point of breaking. If this is what happened, the question is who overtightened that bolt - I would be surprised to have happened on the assembly line, because the car has traveled many miles since. Rather maybe suspension work was done in the past and the bolt was excessively tightened back - way past the stretching point. If this is true, I would quickly inspect and replace all suspension bolts - on both sides of the car.

[oragex]

- Another theory is they inserted the vertical bolt and forgot the nut (honest but potentially fatal mistake)...

Very probable, or simply the nut wasn't tight enough and the bolt just dropped at some point. It would interesting to see if the nut is tight on the other side of the car. I guess it's safer to place that bolt from top to bottom, with the nut underneath - still tightening at the nut but from underneath the subframe

[alschnertz]

Rather maybe suspension work was done in the past

Like the recent alignment at Pep Boys?
Just sayin' Pep Boys wouldn't be my first choice for suspension work - alignments included.

Edit: I should add that I think many "alignment" recommendations from tire stores are not necessary and they will alter the factory settings for no reason.
However, if I know there is an issue, like pulling to one side, uneven tire wear, removal / replacement of suspension components, I will likely have an alignment done.
I just think that most tire stores sell an alignment when it is not required.

[oragex]

Alignment only involves releasing the tie rod locking nut, they woudn't touch the CA bolt

[alschnertz]

Completely agree and alluded to that in an earlier response.
A competent mechanic would know that too.

[cn90]

- Another theory is they inserted the vertical bolt and forgot the nut (honest but potentially fatal mistake)...

Very probable, or simply the nut wasn't tight enough and the bolt just dropped at some point. It would interesting to see if the nut is tight on the other side of the car. I guess it's safer to place that bolt from top to bottom, with the nut underneath - still tightening at the nut but from underneath the subframe...

When I did my suspension overhaul (link above), the vertical bolt/nut has Loctite in it. I had to use propane torch for 30 sec to melt the Loctite to remove the nut.

So, this nut is not easy to come loose by itself, almost unheard of in this forum.
Something fishy is going on in this case...

[hot9000]

@alschnertz @cn90:

By "itemized listing", I meant from the dealership's repair shop, not from Pepboys. I re-edited my post and corrected some other typo's. I don't think the alignment job would touch the control arm/bolt either. Sorry about my bad writing as I misled you.

[alschnertz]

If you're bored today, take a walk around where the incident happened and look on the ground for the missing bolt.
Finding it may answer if it sheared or the nut came unscrewed.
I doubt you drove very far without that fastener installed.

There is no way that running over a curb sheared that bolt yet left no other damage.

If it was my car, I'd have the dealer replace the control arm bolts on the opposite side too.