BMW rear subframe disasters - how often, really?

I've been on the various forums and heard the disasters, but how often do they really happen?

I've heard it said that as long as all the rear bushings are intact and the car isn't flopping about on non-existant bushings, there'll in all likelihood not be a problem - true?

Driving about a day or so ago the wife and I talked about a convertible, and wandering by is a Z3 - I suspect I'd rather enjoy an I6 car. A 'vert and a six, how could one go wrong?

Notwithstanding a Miata would clean it's clock auto-x wise, would the ususal urethane componentry, springs (and/or coilover fronts), and wheel/tire upgrade wake it up significantly?

I'd have to part company with my old gray 320i to make room for it (see what I did there?), but I thinks me could get used to such a car.

Are the tops on them problematic in anyway? I know e36 verts have some issues there...

What sez the collective?

Like anything on the net car forums....there's some truth behind the rumors, but they aren't as common as they seem, because nobody starts a thread that says "Hey, my rear subframe DIDN'T break." The only posts on the subject are when there is a problem, which is "occasionally under the right circumstances." Or so the internet tells me

I have an 11-year-old E46 with 105k or so on it. I've auto crossed it dozens of times on UHP summer tires, but never R comps. I drive it spiritedly every day, and our roads are not fabulous. I've had no issues whatsoever; it looks fine under there. Datapoint of 1.

Z3 has a totally different rear suspension from the 3 series cars. It is a more robust system that bolts to the very bottom of the car like the E30 that came before it.

From what I understand the problem is limited mostly to the non-M E36 and E46 chassis'. Coupes and sedans seem to be the worst. Of the 2 E36s that Ive owned neither had a problems and one of them was a very beaten on coupe. In other words, dont let it scare you away from the chassis but its worth checking before taking the keys.

Friend of mine with a E36 racecar broke his up. It had been ridden hard, and put away wet before he got it- The front half was 3 years newer than the back half, I discovered when I was updating the rollcage.

In reply to mad_machine:

The Z3's are known for some trunk floor/diff mount separation issues, but that's pretty much only on M Roadsters that are tracked heavily on R-comps from what I can gather.

More info: http://forums.pelicanparts.com/bmw-z3-z4-forum/244843-z3-subframe-differential-mount-failure.html

I didn't say it couldn't happen.. but it is more robust as the sub-frame bolts to a stronger part of the car than that of the coupe' and Sedan

In reply to irish44j: I guess that I should do one soon.

Here is what to do about this issue:

Inspect the car carefully before purchasing same. If it isn't damaged and the bushings are good... don't worry about it. If and/or when the bushings need to be replaced, add the reinforcements to the area when the subframe is out. If it is damaged, pretend that it is the end of the world, show the seller the internets and save a couple grand on a sweet car. Go home... repair car with a simple welding operation, new bushings. Rejoice at how useful internet fools are.

This blurb is equally effective for E36/46 and all trailing arm cars including other makes/models that are made of unibody style sheet metal.

I am a bmw technician. The rear subframe problems are usually for the non-M e36 and e46 as stated before. the rear trailing arms on the e36, e46, and z3 are prone to quick wear though. urethane replacements (powerflex, rogue engineering) will decrease the amount of wear and make the car feel a bit more responsive. The stock RTA bushings deflect too much.

-Henry

KazeSpec wrote: urethane replacements (powerflex, rogue engineering) will decrease the amount of wear and make the car feel a bit more responsive. The stock RTA bushings deflect too much. -Henry

Or.... because lathe

I purchased a 2000 M Coupe a few years ago with 70,000 miles in excellent condition. Having read about the issue before I purchased it, I had the car put up on a lift and the mechanic and I looked over the rear subframe and spot welds as best we could. Everything looked fine. It wasn't until a month or so later that I was up under the car with my face right at the differential mount, did I notice two hairline cracks running across the sheet metal diff mount tabs. I pulled all the carpet out of the rear hatch area and found a couple of popped spot welds. I found a few more after removing the seam sealer in that area. I ordered a rear subframe reinforcement kit from Randy Forbes on Bimmerforums and welded it in myself. Among other reinforcements, the kit converts the diff from a single ear mount to a double ear mount cover in the process.

I would inspect it closely if it is a concern for you. But worst case scenario, it isn't a bad fix if you can weld and have a long weekend. Just my experience.

I've been a BMW specialist for 15 of the 20 years I've been a tech. I have seen 2 e46 cars with the subframe issue out of the hundreds, if not thousands, of cars I've worked on.

It's something I would check before purchase, but not something that would keep me from buying one in general.

While it isn't an urban legend, some of it is definitely helped along by abusive driving.

S54 M coupes seem to come up with this discussion quite often.

Well, that sounds pretty reasonable, and about what I'd have thought - but, just because you're paranoid doesn't mean they're not out to get you.

Time to go test drive a few, see how cool they are...