Question about rear subframe failure

[Jeff P]

Throughout this week, there have been several posts regarding rear subframe failures on E36 M3s. I have a few questions for anyone who has been unfortunate enough to go through this breakdown OR who is in the technical-know: (JON CALDITO??)

1. Are there specific years/models that are more prone?

2. What causes the failures; suspension mods, poor-quality sheet metal, excessive track use, etc?

3. What are the symptoms of the failure?

4. Does BMW cover this failure in their warranty or extended warranty?

Thanks!

[Kritpoon]

1. Are there specific years/models that are more prone?

Yes the earlier (95 or ealier) M3 and e36 seems to have this problem. But for 96 and later car, BMW realized this problem and they beef up the rear sub-frame (well trailing arm mounting plate). Though 96+ cars also known to have the problem too, but only the one with heavily modified ... stiffed up... syspension

2. What causes the failures; suspension mods, poor-quality sheet metal, excessive track use, etc?

The main causes of the failure is bottoming out and stiff suspension set up. When you car is bottoming out or riding on stiff suspension, it places a large amount of stress on the "traling arm mounting plate" and the plate being weakly connected to the car will start to crack. Here is what BMWCCA Racing people have to say:
E36 M3 Trailing Arm Mounting Pad Failures Issue date: 5/98
ISSUED BY: MICHAEL YASKIN, NATIONAL CHIEF SCRUTINEER
PHONE: (610)277-6037
FAX: (610)277-6039
E-MAIL: BAVSPEC@AOL.COM


Upon inspection of several E36 M3 race cars we have found the trailing arm mounting plate, also called the toe adjuster plate mounting pad, to have FAILED. The plate is fastened to the body with three 18 mm head bolts, the bolts thread into a threaded tube, the tube is tack welded in two or three spots around the outer circumference to the body , these welds crack and then PULL OUT OF THE BODY .

3. What are the symptoms of the failure?

The symptoms are usually clunking noises coming from the rear of the car when you go over bumps (the sound is very similar to metal grinding against each other) and incline. Also, if you punch it in 1st, the rear end tend to want to swirl side way.

4. Does BMW cover this failure in their warranty or extended warranty?

This one I don't really know, I think it's all depends on the situation. If you have highly mod suspension. It is unilikely that BMW will cover it. They will blame it on the mod suspension comnponents.


And some pictures of failed sub-frame can be found here: http://www.njbmwcca.org/scrapbook/scrap-ltw.htm

[Stylin]

That still scares me..

HEY.. THIS POST WASNT MOVED TO THE SUSPENSION section..??!!??

I dont get it.. see what i mean..

My car doesnt bottom out.. but its pretty damn stiff now... :

[Jeff P]

Kritpoon,

Thanks for the detailed answers to my questions! Much appreciated..

[Greg]

*Changing gearing can effect the mounting points, because some ratios put more strain on the frame, so the tention is transferred to the subframe.

*Slick tires put a lot of strain on the subframe, becuase they don't give like street tires do.

*If you like to do burnouts, you create a lot of axle hop, which beats on that area as well.

*If you live in a snow proned region, salt mixed with any abuse will accelerate this occurance.


Hope this helps