E70 Rear lug nuts came loose/off

[Ozer]

I will check the lugs again when i get the car back for sure. I torqued the bolts myself, 100ft/lbs for sure. Checked them again after doing both sides.

[jfoj]

Not a bad idea when performing brake or suspension work if more than just the wheel is removed to recheck the lug torque after a few days just be make sure something did not shift after driving and a few thermal cycles.

[Doug Huffman]

Originally Posted by jfoj

You could get one of these to verify the torque wrench accuracy.

Typical. Using a complicated device to confirm a simple device. Use a bending-bar torque wrench.

I serviced nuclear reactor plants. A torque wrench had to be verified against a certified standard before use and within eight hours and in the one required direction only.

Metrology is not a simple technology for simpletons.

[ard]

Originally Posted by jfoj

SBUT keep this in mind, not sure what you did during the rear brake job, were rotors replaced? Is the inside face of the rotor fully seated on the hub? Did the parking brake shoes cause a problem with the rotor seating on the hub flange?

I can only assume if the lugs were tightened, something is not fully clamped and moving around. Maybe the wheel center diameter is too small? Clamp load is the important piece of anything being properly tightened.

My vote is that the wheel wasnt fully seated onto the hub...you torqued the bolts, but once the wheel moved and properly seated the bolts no longer held it with any (or enough) clamping force. Rust on the hub, crud, etc could cause it.

[Doug Huffman]

Originally Posted by jfoj

... after driving and a few thermal cycles.

The linear coefficient of thermal expansion for steel is on the order of 10^-5 K^-1 dL/L. Nope.

[jfoj]

Originally Posted by Doug Huffman

The linear coefficient of thermal expansion for steel is on the order of 10^-5 K^-1 dL/L. Nope.

I guess someone is trying to run an Engineering class, the problem is we are dealing with the real world and far too many variables were left out and not assumed.

Everything from corrosion, multiple layers of materials, different materials and even tapered hub centric wheel centers. We have no idea if the wheels are OEM and the proper ones.

I choose to err on the side of caution or add an additional safety factor and verify wheel torque again after a few drive cycles. Even many national tire stores recommend a revisit to verify wheel bolt torque.

[the_ulf]

i'm wondering, is this not a thing anymore to re-torque your wheels after a few miles of driving?
i don't even *torque* mine so much, FT usually suffices. once i had a wheel off for whatever reason, i usually check about 100 miles later. it's not unusual for a wheel to re-seat itself during the first few miles after replacing, so checking tightness of the lugs is always recommended.

[DefSR]

Originally Posted by Doug Huffman

Not possible.

A particular steel alloy, that I am familiar with, yields from elastic to plastic deformation at 80 Ksi.

Ugh... such misinformation.

You can easily yield a lug bolt with excessive torque from a breaker bar/impact gun. They are almost certainly Class 10.9 fasteners, which have a yield of 940 MPa, or ~136 ksi. The hub doesn't even need to be nearly as exotic from a yield strength perspective due to the strength advantages internal threads enjoy over external threads.


OP, I'd say you either never got them properly torqued up at the last service/time the wheel was off, and never got it right on the side of the road, or more likely, the bolt threads were stretched and subsequently didn't have good engagement as the bolts were subsequently stretched more and more as they were retorqued.


The remaining lugs not being able to be removed is a bad sign as well, as that might have damaged the hub threads due to bending across the lugs since there were only 2 on there.

[Ozer]

Alright guys i got the car back last night.
So my mechanic was able to save the hub, he had to thread 3 of the 5 bolt holes and get new lug bolts. After talking to an Indy BMW shop owner, im going to assume that i didn't seat the wheels properly.I got the bolts hand tight, put the car down all the way and then torqued the wheels so they may have gotten cocked or something. Proper way to do it is to hand tighten, put down just enough so the tire touches to prevent spinning and then torque and lower vehicle he said. Also re-check after 100 miles.

I have these brake dust shields that go inside the wheels which make it a pain to see when putting the wheel on the hub, that may have caused some issues for seating the wheel as well. The remaining 3 are coming off this weekend.
Thanks for all the help and suggestions.

[jfoj]

I snug the lugs up pretty tight before I even rest the vehicle on the tire. Pretty easy to do with a 1/2" torque wrench or breaker bar. The mass of the wheel/tire does not rotate quickly when you really "snap" the breaker bar or torque wrench. If needed, you can even get the wheel/tire moving and the then use the rotating mass of the wheel to tighten the lugs up, braking the moving wheel with the breaker bar/torque wrench. I am guessing I can easily get 50+ ft/lbs of torque on the lugs with the wheel free from the ground.

Kind of hard to explain, but I have been doing this for years.