Lower control arm bolts backed out.

[jimbrownlowe]

2018 Model 3: I was in a parking lot and heard a loud “clunk”. I looked underneath front end and found a large bolt on the ground. Further inspection revealed another bolt partially backed out. Bolts were from the lower control arm of the steering mechanism. Rendered the vehicle undrivable.

What could have caused the bolts to back out to the point of one falling completely out?

 

[E90alex]

What could have caused the bolts to back out to the point of one falling completely out?

Poor quality control

 

[Kimmi]

It’s a 2018 so the quality control got it this far. I would ask if a wife or husband had recently taken out an insurance policy?

 

[The Other Dan]

Not the first time that's happened. They are relatively easy to put back in though if you've got the mechanical ability.

 

[TimTam]

2018 Model 3: I was in a parking lot and heard a loud “clunk”. I looked underneath front end and found a large bolt on the ground. Further inspection revealed another bolt partially backed out. Bolts were from the lower control arm of the steering mechanism. Rendered the vehicle undrivable.

What could have caused the bolts to back out to the point of one falling completely out?

Lack of Loctite
Excess lateral loads
Early mistakes in design by Tesla

Swap in a Mountain Pass FLCA bearing, use loctite, torque to 95 lb-ft, check yearly or more often if clunks are heard

This may have been fixed (let’s hope so!) on highland. The FLCA and FUCA on early to mid production Model 3s are a notorious point of failure due to (probably unanticipated) second and third order effects (hesitate to say design flaws, but in retrospect, maybe the phrase fits).

 

[blrt]

I am exploring the option of replacing it with a longer bold and an additional jam nut if room permits?

 

[The Other Dan]

If you're going that far, just do the MPP replacement.

 

[gearchruncher]

I am exploring the option of replacing it with a longer bold and an additional jam nut if room permits?

If you are serious about doing work to fix the backing out issue, it would be much easier to drill the bolts for safety wire or put a thin metal plate under the bolts and fold over tabs onto the bolts. This is how it's actually done in safety critical applications.

But these bolts don't back out on 99.9% of cars, just torque them correctly and they'll be fine.

 

[brkaus]

Add our 2018 3lr to the list.

 

[Collutio]

If you're going that far, just do the MPP replacement.

In the context of this thread the biggest benefit of the MPP bearings is that they add a crush tube. The factory bolt can be torqued correctly but sometimes still wiggle loose. Where they bolt in doesn't have a crush tube to ensure all of the torque is applied from bolt to nut; some of the torque compresses the surrounding structure instead. I'd be interested to know if anyone has ever turned up some crush tubes for the factory part, it'd be easy enough on a lathe if you already had some stock with the right ID.

If you are serious about doing work to fix the backing out issue, it would be much easier to drill the bolts for safety wire or put a thin metal plate under the bolts and fold over tabs onto the bolts. This is how it's actually done in safety critical applications.

If you have the tools and expertise to lock wire the bolts correctly it doesn't get any better than that. I'm not sure what you'd tie the lock wire to in this case, the bushing sits between the bolts so they wouldn't be suitable for wiring to one another.

My arguments in favour of the MPP part is because of the improvement in steering response and durability, so it's a multi-purpose upgrade if you're already removing the arm. I could see a long bolt and a jam nut working by providing a means other than bolt torque to hold the bolt in though. If you already had the right grade and size of bolt lying around it'd be cheap and easy.