BMW Z4 is the unibody bent or not bent, that is the question


Hello, I am in the AF, and last week when I was driving through the gate, the Security Forces troop accidently raised the barrier on my vehicle (BMW Z4) while I was driving through the gate. The impact was loud and sudden. It raised my car up and then dropped it down littering the street with plastic and rubber parts. I have been waiting an week for an estimate on the vehicle. There is damage to the front end and ofcourse undercarriage of the vehicle. The check engine light came on immediately. For some reason I cannot get a straight answer on whether or not the “frame/unibody” was bent in the accident. How can I tell for sure? BMW says they can only tell by taking it appart, however the insurance approved garage put it on the lift and said “it looks pretty good”. Thank you for any help you could provide. Sincerely, Bryony

Modern unibody cars have “crush zones” that are designed to crumple in an accident…The structure simply folds up in a controlled way…“We can pull the frame back”…Those are hollow words…

You made no mention of airbag deployment, if the bags did not blow, that’s a sign the impact was not TOO severe… However, there are lots of expensive parts that could have been damaged…

Do both doors still open and close the way they should??

Thanks caddyman. The airbag didn’t deploy, however the airbag light came on. On the passenger side near the gear box the plastic bubbled up as if there was some electrical short and intense heat… Not a good sign! Are the crush zones visible when the car is on the lift? BMW acted as if they wouldn’t be able to tell unless they “took the car apart”, but the insurance approved body shop said they could tell from looking at it on the lift. I just want to make sure that the car is structurally sound.

Why are you dealing with “the insurance Company approved garage”. don’t you have any choice? I would tow it to the BMW dealer and let them deal with the insurance company.

Mr. Bryony,

I have scant experience in this area but have a rough feel for the legal environment in this area after I was rear ended by a drunk driver last year at low speed. My car needed to have the body pulled back an inch or two and that was done at a body shop. I thought that I would have the remaining repair work done in stages as I had time to get competitive quotes at my leisure. When I went to another shop to get a quote to have the remaining metal distortion (dents) in the right rear fender, the rear splash apron and the rear body panel below the hatch lid repaired, the body shop refused the work due to liability concerns. The reason given was that if I had another collision and was injured, my lawyer would argue that my car was weaker due to previous damage and that all parties involved including the person who simply took the dents from my car would be dragged into the potential resulting lawsuit as defendants.

This may have body shops running scared. If you would Google “metal work hardening” it appears that it may be possible that minor steel deformation may actually strengthen your car’s body structure but I don’t know that for sure and the legal profession may be profiting from everyone’s ignorance of that feature of metal including steel.

BMW may not want to touch your car and are simply blowing you off. The body shop that you contacted may be correct to some extent and is not vulnerable to a lawsuit if they did no work on your car; and also is simply blowing you off.

Keep this in mind as you search for someone with adequate business insurance to repair your car.

If all the doors, hood, and trunk are lined up, latch properly, and have the same “gaps” as before you are probably OK and the frame isn’t bent. But, the only way to know for sure is to precisely measure the frame and this includes looking to see if it is torqued as well as shortened.

Looking at the car, even on a lift, is only going to give you a "quesstimate, that the frame is straight.

My thought is that the car is not designed to be hit in that area then dropped, you dud not say what year this car was but I would push to have it totaled. This sounds like one of those cars that may never be right again. Especially if the dash lit up like an Xmas tree after it happened.

Ps did this gate have the poles that rise up, or a long jersey barier type of gate, or the type of gate that arcs open?? In other words was it lifted evenly across the entire bottom or in one spot??

First this car need to be put on a frame rack and checked. Second Unibody cars can be repaired. Its just not a mater of pulling out the bent parts. These parts have to be replaced. Any shop that tells you they wont work on a car that been damaged will be for 2 reasons - 1 They have no clue how to do it right. 2 - The car is totaled and can not be fixed safely. Unibody cars can be safely repaired back to factory specs. Its done everyday. You can even clip them if you know what you are doing.
My guess is the airbag sensors were damaged. You were going to slow to to have the airbags deploy. This car should be able to be repaired. What will keep it from being repaired will be cost and the remote possibility something is damage that cant be fixed.
To UncleTurbo. You are partly right. It will need to be measured. Most cars today have only 3mm tolerance in the body. You can have all the doors fit and sill have a bent unibody. I worked on a car once were all the lines looked fine. It all came down to how the left headlight fit. The left rail was sill bent up a few mm.

Thanks everyone, I have attached some pictures of the barrier and the car. Most of the damage was caused by the barrier catching the car undercarraige and then closing and ripping the fender liner? out as i cleared the barrier. The car is drivable and all doors close properly - in all doesn’t look too bad. However i am told those barriers are built to stop dump trucks and deploy several hundred pounds of force, which is why i am concerned about the frame. I am lucky that it struck the front of my car and they put it down right away. I have head of these barriers flipping cars. My car is a 2005 BMW Z4 with the sports suspension package.

  • Bryony

If the body structure was tweaked, the doors usually no longer fit or open and close properly…But major damage was certainly done…

If it picked up the front of the car, i’d make sure the shop thoroughly checks out the radiator, a/c condenser, front suspension/steering, oil pan, etc etc…even things like brake lines. There’s a lot of intricate stuff up there that wasn’t designed to withstand an impact like that.

"The airbag didn’t deploy, however the airbag light came on. On the passenger side near the gear box the plastic bubbled up as if there was some electrical short and intense heat… Not a good sign! "

No, not a good sign at all…

If the unibody were tweaked, you’d either feel it in the driving or see it in the alignment of the doors and windshield/hood area. If everything is aligned and it drives fine, you’re good to go.

It appears from the photos that the gate came up forward of the tires, under the car. The unibody atructure typically comes justbarely forward of the front strut, typically well braced by the transverse support assemblies. The area forward of the wheels is generally a crushable zone comprised of the radiator support structure, the front of the inner wheelwells, the radiator, and misc bracketry that holds lighting, the airbag sensors, the horns, and other such. That assmblage is much weaker than the portions forward of the transverse members (which hold up the engineand/ot tranny and hold the front suspension components in place). It’s pretty tough to torque the body out of whumpus by pushing up on and section forward of the wheels. I don’t have the BMW drawings, but I posted mine, which are pretty typical for this type of structure overall.

I’d ne more concerned about the radiator and tranny cooler and their associated tubes and support structures. And I’d be sure there’s no damage to the airbag sensor as well.

By the way, the only way to definitively check the body is on an “frame alignment machine”. It’s a huge table with measuring equipment built in along with huge hydraulic rams and chains. Using one generally requires some disassembly to get to the unibody measurement “pickup points” to measure whether the unibody is still within spec. It wouldn’t be cheap.