Us non-M guys have the same problem...

[janikphoto]

Looks like us 2.8L guys have to worry about the rear diff mount, as well...

[ajt36]

Yup… RF took care of mine last year, though it was just my welds in the trunk starting to pop.

[BimmerBreaker]

Happens to 1.9's too It's not an M problem, it's a Z3 problem...

[Randy Forbes]

Caution, if you have a weak stomach; this is the 3.0 Coupe I'm working on right now...

The actual differential mounting bracket in this particular car didn't look bad at all, but the structure around it is another story! I have long maintained that there are two (2) distinct areas of concern; the strength of the trunk floor itself, and the integrity of the individual mount. Some cars will exhibit problems with one or the other, and often times, both.















And for anyone that thinks the additional stitch-welds applied at the factory during mid-year 2000 production did any good, here's proof they didn't.



Repairs are underway, and along with this simple task, the car will also benefit from the installation of a complete TC Kline (single adjustable) C/O suspension and new rubber throughout.

For anyone doing this at home, I recommend ALL CRACKS be stop-drilled (1/8" hole) immediately past the end of the visible crack. You need to relieve the built up stresses in the metal, or the crack can continue after it has been welded (I haven't seen that happen personally, but it is what they teach all the airframe mechanics to do, and the FAA makes sure they do it).









Before any repairs are made, the XMBR is pulled back up into position.







I don't post too much of this sort of thing anymore, unless the subject is brought up, because, you know, I don't want to get a reputation for posting ugly pictures.

[MrDangles]

^golly

[ajt36]

Once you get under your car after Randy has fixed it and see that robust triangle shaped diff mount, you wonder how the hell BMW could ever have justified that diff ear that looks like a thin piece of tin and those "spotty" spot welds in the trunk.

[janikphoto]

Once you get under your car after Randy has fixed it and see that robust triangle shaped diff mount, you wonder how the hell BMW could ever have justified that diff ear that looks like a thin piece of tin and those "spotty" spot welds in the trunk.

It really is thin and weak. I saw it and thought, " Is this my Z3, or did I accidentally slide under an 80's era Hyundai?!?"

[BMWBergy]

Baaarf!!! I feel ill.

[Badger56]

Not exactly the hairline cracks we sometimes see in aviation. Makes me wonder how BMW will design the new carbon fiber components. I mean, unlike metallurgy, we "know" so much about composites. And, to my knowledge, flaws in composites can be harder to detect - let alone repair. Randy F. could have a whole new future.

[janikphoto]

I looked in my trunk today, and there's a lot more damage than I first thought. Not fun.

[bagekko]

I dont understand how there is no rhyme or reason to cars it happens to. Friends 98 M Roadster 225k miles driven in winters, not a stickler for maintenance, and his is fine. My 00 Z3 2.8 85k miles, garage queen, no problems either. But Randys pic above of a 01/02 3.0 with a destroyed rear underside. Why does it seem to be inconsistent?

[rf900rkw]

This is a cyclic stress failure. It has everything to do with driver input, zero to do with the frequency of oil changes.

[janikphoto]

I'll admit that I gave this car plenty of input! I enjoyed feeling the torque push me into the seat.

[rf900rkw]

Aggressive and abusive driving is one way. Personally, I ripped the mount by doing on road testing of some transmission developments. We're talking banging shifts, clutch dumps, that sort of thing for over a year. Some people drive like this naturally. But even mundane drivers can rip it up. There are people out there that can not hold a steady throttle. They drive by making constant pedal adjustments; micro-stabs at the pedal. The loads on the mount reverse like every second. A few million cycles of this and things start coming apart.

[BMW135]

That is exactly why I had the RF kit done long before there were any indications of issue. Why wait? The peace of mind knowing my trunk floor isn't going to rip out was more than worth the price of admission.. Plus the rear end feels so much more solid!

[Remotion]

Some day someone will make these trunkfloor parts from carbonfiber with titanium bolts etc... Even in todays tech it would be quite easy and not so super expensive let alone in future.

[spacecowboy]

There are people out there that can not hold a steady throttle. They drive by making constant pedal adjustments; micro-stabs at the pedal. The loads on the mount reverse like every second. A few million cycles of this and things start coming apart.

The old "Stab and Steer" method?

[spidertri]

Lol stab and steer, first time I encountered someone doing that I couldn't help but ask why they were driving like that.

This does make me more nervous because the dumb dual mass flywheel in these cars makes it so hard to shift gears smoothly. I've gotten used to it but occasionally there is still one of those super clunky shifts where you can feel the flywheel rebound and shock wave travel down the driveline.

Someone stabbing the throttle would really screw with the DMF and driveline in general.

My 318ti still has the DMF but it shifts/drives much more smoothly and I track that car regularly. Still has stock clutch. Much less torque though.

[rf900rkw]

The old "Stab and Steer" method?

I was talking about going straight down the highway. But yeah.

[Randy Forbes]

My dad always drove with one foot on the brake, and the other on the gas__I can't ever remember seeing him drive a stick, but I knew he knew how, as some of the old cars he'd bring home from the (used car) lot were Metropolitans. He didn't "own" a car from the time I was born in '54 until the new Valiant came out in September of '59__he just always brought home something that was for sale on the lot where he worked; frequently they were Hudsons, Packards, Kaiser/Kaiser-Frasiers, Nashes, all the weird stuff.

But anyway, he brought stab 'n' steer to a whole new jerking fore & aft level!