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When I'm shopping for a second hand car, I often hear an advice to find out if a car has been in a major accident and refrain from buying in this case. When I tried to find out why that is, I was told that this is because of possible "structural damage".

But if the car has been fixed after an accident and drives nicely, what are the actual risks? Why "structural damage" matters? Is this a safety risk, or potential maintenance cost, or what? Please be specific.

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    Welcome to Motor Vehicle Maintenance & Repair! – Pᴀᴜʟsᴛᴇʀ2 Dec 15 '17 at 1:16
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    be specific? What do you expect as a specific answer to such a general question? – agentp Dec 15 '17 at 3:57
  • Not enough for a full answer, but my car was in a major accident, and the wire for the brake light switch failed a year later. The wire was cut almost all the way through in the accident, and it was not noticed or replaced. If I wasn't handy with a soldering iron, it would have cost me around $200 - or the person I sold the car to if I had sold it. – JPhi1618 Dec 15 '17 at 15:17
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From my understanding, the primary concern is the frame itself. If the frame is bent or damaged, it can alter all sorts of vehicle geometry, and even small changes can have a big effect. A simple example would be a bent radiator support. If this wasn't properly repaired/replaced, then the radiator would not cool as needed and could lead to further engine damage. Likewise, if you had steering misalignment that could cause worsened handling and excessive tire wear.

Another aspect (that will vary depending on country and laws of a given jurisdiction), is that you don't have the right or ability in many cases to chase up the repairmen for faulty work. Meaning, that if a person got in a accident and had a new transmission installed, then you bought the car and agreed to "as-is" and the transmission went bad after 100 miles - you'd have no ability to leverage the company to fix whatever it messed up!

Basically, when a car is in an accident, there are A LOT of things that can get messed up, and it's near impossible to be 100% certain that none of those things are perfectly fine without fully tearing the vehicle apart and measuring everything against factory spec (which, needless to say, no one wants to spend the time doing). That is a very time intensive and therefore costly endeavor.

  • Good point for #2. But re #3: for the most part, you don't actually need for all those things to be absolutely perfect, right? Maybe it's not great if the door on one side closes a little weird, but if it saves you $2000, maybe it's worth it. – Cullub Dec 15 '17 at 4:40
  • Cullub - doors are easy to check, and not really much of an issue. But it is not easy to check every structural member, every weld, engine mounting bolts, control arms etc. These are things which if they fail when you are at speed could be life threatening. – Rory Alsop Dec 15 '17 at 7:16
  • @Cullub That's right, small things like that may not be much of an issue, but as Rory points out, it's a problem of ensuring that everything is OK. – kyle_engineer Dec 15 '17 at 18:31
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tl;dr: Major structural damage can induce so many different types of risks that it’s usually not worth investing your time or money.

When I'm shopping for a second hand car, I often hear an advice to find out if a car has been in a major accident and refrain from buying in this case. When I tried to find out why that is, I was told that this is because of possible "structural damage".

This is good advice and it is easy to see why from the very beginning:

  1. You won’t know the specifics of the “major accident.”
  2. You won’t know exactly how the vehicle was repaired.
  3. You do know that it wasn’t repaired in the factory that specializes in making these cars.
  4. You don’t know what was damaged but not repaired and is waiting to fail.

All of those say to me “keep looking. There are plenty of cars out there.”

But if the car has been fixed after an accident and drives nicely, what are the actual risks? Why "structural damage" matters? Is this a safety risk, or potential maintenance cost, or what? Please be specific.

Unless you know all the details, the risks are essentially infinite:

  1. Has the car’s ability to absorb the next major collision been compromised? If the frame was “straightened”, that doesn’t mean the car was returned to its original crash rating.
  2. Has the car been repaired to factory specs in terms of rust and deterioration?
  3. What difficult to inspect parts were also impacted but not replaced? For example, are the wheel bearings slowly eating themselves now? How about the power steering pump?
  4. What work wasn’t done because it was too expensive?

In the end, I would stick by the original recommendation: you usually shouldn’t bother with the result of a major accident. If you choose to do something different, caveat emptor.

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The underlying issue is that major accident damage is likely to cost more to repair properly than the vehicle is worth so there is always a risk that repairs have been done on the cheap and are largely cosmetic.

Equally structural damage can be very difficult to diagnose and often a car will be written off by an insurance company without anyone ever assessing the full extent of the damage once it is clear that it is beyond economical repair.

The real problem is that there is no real way of knowing the extent of the damage and how well it was repaired.

Another big issue is that modern cars have sections which are designed to deform in an impact and absorb energy and, equally a strong survival cell to protect the passenger cabin. If these have been compromised in an accident there may be no obvious signs untill you have a accident and the car splits in half.

This is no to say that all cars which have had major accident damage repaired are unsafe but overall it is generally not worth the effort required to assess them and much easier all round to just look elsewhere.

In terms of actual risks potential issues include

  • Sudden failure of improperly repaired parts like suspension mounts, steering components etc are all very dangerous
  • Compromise of the function of crash structures
  • Misalignment of suspension or drive train mounting points causing excessive wear or poor handling.
  • Compromised corrosion protection
  • Poorly executed welded repairs may be subject to sudden failure.
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I drove a Volvo 240 that had the chassis straightened after an accident - drove fine - never did the wing that showed slight damage though.

This very much depends on who you get to do the work - a good shop and it will be fine : a “cheap” place and the problems could be endless...

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