Rear sub-frame problems

[Tom Shaffer]

How wide spread is this issue? I'm looking at a 98, should I be overly concerned. The car has a clean bill of health from the dealer that has serviced the car.

[Jeron]

You probably wont find your answer here but you should be mildly concerned, so don't get it until you find your answer. There are some good Z forums.

[DEAN911]

I have a 2001 3.0 Z3 with the full Dinan set up. Over 50,000 miles and no problems. I also treat the car right. I drive fast but I am not abusive. I never drag race or autocross. Look up Randy Forbes on the other BMW boards. He fixes this problem and has a wealth of information on the subject. Bottom line, inspect very closely and double check that. The fix is not cheep.

[Schneller]

In our experience the beater cars & track cars have rear floor issues. BMWs aren't drag nor drift cars. If you like to light 'em up then you'll be cracking the rear floor.

Do a pre-purchase inspection w/ a reputable BMW shop. They'll know what to look for and save you money in the long run.

Schneller

[chgrec]

Originally Posted by Schneller

In our experience the beater cars & track cars have rear floor issues. BMWs aren't drag nor drift cars. If you like to light 'em up then you'll be cracking the rear floor.

Do a pre-purchase inspection w/ a reputable BMW shop. They'll know what to look for and save you money in the long run.

Schneller

There is a lot of evidence that these cars are prone to weld failures regardless of the driving style. Abuse by drivers or poor quality engineering on BMW's part?

Some facts about this tear issue:
- Occurs in all model Z3s & MZ3, even with 1.9 liter engines
- Appears to be more prevalent in 2.8 and larger engines.
- Initial tears are invisible to casual inspection. Requires detailed investigation of Differential sub-frame & trunk with tool kit trays removed

A few non forum web sites that illustrate the issue
http://www.thelargeglass.com/bmw/subframe
http://www.z3power.net/Nfong_CrackFrame.html
http://dinancars.com/SeriesPrint.asp?prod=1282
http://www.thelargeglass.com/bmw/subframe/


There are numerous discussions about this issue on all of the BMW forums, so it isn’t an isolated issue or one caused by abuse or accidents.
http://forums.bimmerforums.com/forum/showthread.php?t=401478
http://forums.bimmerforums.com/forum/showthread.php?t=402183
http://forums.bimmerforums.com/forum/showthread.php?t=426899
http://forums.bimmerforums.com/forum/showthread.php?t=390791
http://forums.bimmerforums.com/forum/showthread.php?t=402329

Chris

[Schneller]

Chris,

Interesting stuff indeed. The photos you linked are however extreme failures where an initial crack was left unattended for a long time, progressed, and then compromised other areas of the rear floor. Failures like that don't all of a sudden happen. In our experience, a car like that would have been clunking a long time before all the floor spot welds snapped. A prudent owner should have addressed that long before things got out of hand.

There's no doubt, based on your links, that the Z3 floor isn't as stout as an e30 for example, and there obviously are some failures.

We however haven't seen much of it at our shop. In the more extreme end of our Z3 customer base, we have 2 MCoupe track customers. One customer has 70K miles on his supercharged S52 that has well over 50 hard driver schools on it. We repaired one 1/16 inch long crack near a spot weld at the diff mount. Nothing else has developed on this car. The other customer had a 50k mile S54 Supercharged coupe w/ similar use. His diff mount & floor was intact. Of the remaining street Z3s in our customer base (about 17) we have not seen the problem develop.

I'm not saying it doesn't happen. What I am saying is that if the floor is weak and a crack starts it needs to be addressed. Else it will travel like a crack in your windshield. Furthermore, assuming that the Z3 rear floor is weak, then hard driving coupled w/ rough roads isn't going to make it last any longer, and will certainly lead to failures.

If you're buying a car and don't know what to look for relative to this issue, then have someone who is familiar with it evaluate it. If you plan on buying a Z3 and intend to use it hard, then have someone add more welds to the affected areas for some added insurance... and stay away from hard urethane subframe & diff mounts.