Help - unidentified bolt snap while changing tire

[cmbenedict]

Any help appreciated. Was changing winter tires to summer tires (finally) and was lifting the drivers rear side to remove wheel when I heard a pop/snap near front of X5 (2006 4.8is with air suspension 4 corners). Found bolt head under vehicle with 10.9 inscribed on it. Had to finish last 2 wheel swaps then took for a short drive. No issues in handling or any weird sounds. About quarter mile I heard another pop and saw something in rear view on road. Was other half of bolt - they fit perfectly.

Can anyone identify the bolt by its markings? I figure it’s attached to frame somehow and the flex when on jack over stressed it. What should I look for? Don’t have a lift so I will have to take to shop. Need to know how critical it is (immediate no drive situation or I can take somewhere).

Thanks in advance

[wpoll]

That looks to be one of the six bolts that holds the front reinforcement plate in place - the large alloy (or steel on the 4.8is?) plate under the engine. This plate is critical for front subframe integrity.

Check that there is a bolt missing - and note that four of them also retain the sway-bar bushings. If one is missing, you are probably OK to drive to a shop but you'll want to get it sorted before driving too far.

*edit* - yellow and green arrows here: -

[cmbenedict]

Terrific, thanks Wayne. I will get it to shop and on lift in morning. If I can slide under I’ll get a look and pics.

[andrewwynn]

As [mention]wpoll [/mention] said, four of the bolts hold the anti sway bar and wow what a racket if you drive with them loose! (I had to go get a part and shop is a mile away, had the six bolts finger tight).

The bolts are torque to yield when properly installed. You can actually TTY them about 2-3x past the factory install but that one is clearly overcooked.

I swapped mine all out for 12.9 bolts so I could reuse them and used nordlock washers to keep them tight.

12.9 overlocked about 10% gets your as much compression as 10.9 TTY and you can do it ∞ times.

Nothing special about those bolts other than captive washers and the nuts are crushed to make them stay tight. You can get 10.9 bolts and nuts you can even “ovalize” the nuts just like the factory if your want to properly install them TYY and have the nuts stay on.

I put mine on bolt on top made it much easier to service the next time.


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[cmbenedict]

Thanks, great info andrewwynn!

[cmbenedict]

Wayne thanks, you were 100% right. Rear most bolt on passenger side. Should I replace all 6 or just the one?

[andrewwynn]

Based on the one being abused I'm confident the rest were as well.

The stiffening plate makes the car rigid, if the bolts aren't stupid tight it's not performing it's duty. If the bolts were reused and torqued they can't be torqued properly after ≈ twice as they will be plastically deformed.

I did destructive testing on a handful of these bolts. On the third tightening every bolt failed; no longer could tighten, could feel them stretching before I could TTY.

[cmbenedict]

All 6 it is. Thanks

[andrewwynn]

I would do some destructive testing on the rest of them see if any of them can even get to 90 foot pounds of torque.

my memory is a little bit rusty, but when I did my destructive testing the initial torque of 65+90° might’ve been Newton meters would bring them to about 90 - 95.

on the third attempt, they would just start stretching at about 70 foot pounds and would not go above 70 until they snapped.

it was a very weird experience, watching the torque stay the same while I was turning the wrench.


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[Henn28]

How does that snap!? Has the plate been on and off and the bolts reused many times? I reused mine a few times and then replaced them with OE bolts as I started get nervous. Years ago I took the car to a shop for suspension work and they neglected to properly torque these bolts. The car made a nasty racket amd was clearly unsafe.