Z4M Frame issue... If you track your car look at this thread!

[F360C]

So I went to the track on saturday and did about 4 sessions. During my third session I am chasing down this EVOIII with a 11,000rpm built motor. I hear this pop and think "oh no the motor mount bolts have broke again." I pull into the pits have a look over the motor and see that the motor mount is still perfectly in place. Do a quick visual inspection and can't find anything wrong so I head back out. The car no seems to have a touch more over steer then normal. I just chalk it up to the rear tires getting to hot. I normally like a happy rear end so oversteer is nothing new but I still have a slight knocking soundevery once in a while. Car is running fine so I don't think much of it.

Fast forward to last night and I am taking apart the front end the car to remount my front splitter. I notice one of the brackets to the sway bar sagging a bit. Perfect...I just found the knocking sound that I heard yesterday! I go grab a 13mm socket to tighten it up but when I go to tigthen it I notice the the bolt is moving with the bracket and not only that but the entire bar is movining too! Below are pictures of what I found. Both the passenger side studs in the frame that you bolt the sway bar brackets to have ripped right out of the frame! One of the drivers side studs is 90% out and the other has a bad crack around it. Great so this totally ruins my 3rd of July night! I don't know how I am going to fix this yet. As you can see from the pic of the sway bar the studs don't have much surface aream. I am thinking I will just have a shop weld a steal plate to the bottom of the bracket but I gotta talk to some race shops to see if that will work.

Alot of BMW's as of late are having frame issues. The Z8, Z3's, e46s and now the Z4M. I know I do push my car harder then most people but I didn't suspect this being a weak point. If you track you car you should inspect the sway bar frame mounts for cracks so it doesn't get to the point I am at.

[johanness]

YIKES!

Let us know how u make out. Food for thought...

[inTgr8r]

Damn, that looks nasty Adam!!!
IIRC you are also running GC gold sway bars?

That would also load up (stress) the mounts more than the OE bars.

[thekurgan]

Track or no track, this looks bad. I would think street-driven vehicles would see worse conditions even with the stock sway setup.

[F360C]

Originally Posted by johanness

YIKES!

Let us know how u make out. Food for thought...

I will be sure to keep everybody informed of the outcome. I have my fingers crossed it will hopefully be something as easy as welding a steel plate over top not unlike they do for the e46 subframe reinforcement.

Originally Posted by inTgr8r

Damn, that looks nasty Adam!!!
IIRC you are also running GC gold sway bars?

That would also load up (stress) the mounts more than the OE bars.

Yeah I almost choked when I saw the damage! I went stright to the fridge in the garage and cracked myself a cold one.

I am running the GC gold front bar and the white rear bar. I was thinking that because of my high spring rates (600F/750R) my bar would have to work less but I think my logic might be flawed. This was the last place I was expecting to break. With the way I drive this car I know a weak point was going to pop up sooner or later. I guess now I am just going to have to find a way to make it stronger. I am going to have to take a look at my brothers tomorrow and see if I can see any cracks developing in his.

On the up side I was able to get my "inTgr8r rear splitter support" fab'd up and installed. Tomorrow the plan is to put the "inTgr8r wind blocker" on and get the bumper all put back on. It will be interesting to see how the car handles once I try to dial it in for next weekend without a front bar. No way I can get that fixed in time.

Originally Posted by thekurgan

Track or no track, this looks bad. I would think street-driven vehicles would see worse conditions even with the stock sway setup.

Yeah I was suprised too! I can't remember the last time I hit a pot hole. I thought the endlinks would snap before the studs pulling out of the frame. Hell I would think the aluminum GC sway bar bracket would snap before a steel bolt would pull out of a steel frame. I guess the American made GC aluminum is stronger then German steel! haha

[z4mnyc]

Good post, thx. I'll have to inspect my car for this.

[MIKe86]

Damn. I hope you report it to BMW NA. Would be nice if they reimburse you or take care of the problem themselves - but even if they don't it may help others down the line to have documented cases of it now like the e46 rear subframe. My buddy has an lsb e46m, its an 01 but with updated/reinforced rear and it still ripped out couple weeks ago. BMW is taking care of it even though the car is 10 years old.


On a side note, I owe you a reply pm oops! Pm'img now.

[shitbrownMcoupe]

Yikes! I'm afraid to take it to the track now!!!

good luck and those pics gives me the goose bumps!

[thekurgan]

That does look like thin steal ... def needs a reinforcement plate of some kind.

[psygnosis]

would this be an issue for all e85/e86 cars or just the M versions?

[Beedub]

This happens reguarly with stiff suspension and beefed up bars, the eventual stress does things like this.......

Modding always has a effect somewhere ;-) this is one of the reasons i dont like road slicks and comprehensive suspension mods....

Byron

[onelove]

Sucks to see that but agree, stiff suspension and beefed up bars = more stress than the area was originally designed for. It still shouldn't fail, but just gives you a reason to beef up that area. Have them take some sheet steel and drill new holes, stitch weld in place and you should be good to go!

[F360C]

Originally Posted by Beedub

This happens reguarly with stiff suspension and beefed up bars, the eventual stress does things like this.......

Modding always has a effect somewhere ;-) this is one of the reasons i dont like road slicks and comprehensive suspension mods....

Byron

Originally Posted by onelove

Sucks to see that but agree, stiff suspension and beefed up bars = more stress than the area was originally designed for. It still shouldn't fail, but just gives you a reason to beef up that area. Have them take some sheet steel and drill new holes, stitch weld in place and you should be good to go!

I spoke with some Engineers today and my buddy who owns a rally car prep shop and they all say that with the spring rates I am running the sway bar should have to work less then if I was just running the larger bar and stock spring rates. The higher rate springs are doing more of the work the bar would normally be doing to control the roll. Thats not to say the bar is not putting more stress on the mount but that the high springs rates have no bad effect on the sway bar mounts.They just chalk this up to weak material at the area of the studs.

[Shipkiller]

Thanks for the update. Just one more thing to check before and after every track event.

[Serious]

The magnitude of the force isn't what causes failure, it's the constant cycling that fatigues the subframe and causes the failure.

If you're actively tracking any BMW built after about 1992, prepare for some form of metal fatigue failure.

[F360C]

Originally Posted by Serious

The magnitude of the force isn't what causes failure, it's the constant cycling that fatigues the subframe and causes the failure.

If you're actively tracking any BMW built after about 1992, prepare for some form of metal fatigue failure.

This is exactly what the engineers said was the cause for the failure. Thin steel that was flexing back and forth eventually led to the metal becoming weak. Not much unlike the e46 subframe failure.

My buddy who has the rally prep shop is going to be welding a plate on there for me this week. He say it should be stronger once the plate is on there then it was before the mount tore it self up.

[thekurgan]

Originally Posted by F360C

This is exactly what the engineers said was the cause for the failure. Thin steel that was flexing back and forth eventually led to the metal becoming weak. Not much unlike the e46 subframe failure.

My buddy who has the rally prep shop is going to be welding a plate on there for me this week. He say it should be stronger once the plate is on there then it was before the mount tore it self up.

It might be lucrative for your buddy to manufacture a plate to be sold here so this issue is alleviated to some degree? Just sayin'

[MIKe86]

Originally Posted by Serious

The magnitude of the force isn't what causes failure, it's the constant cycling that fatigues the subframe and causes the failure.

If you're actively tracking any BMW built after about 1992, prepare for some form of metal fatigue failure.

Why 1992?

If I'm not mistaken that's around the same time the Bethlehem Steel plant shut down (which I was actually at to watch the fire works this 4th ). I didn't think they provided any steel for vehicles but I'm curious if there's a connection.

Pardon my ignorance it's a bit before my time and I really should do someore reading on my local history..

[F360C]

Originally Posted by thekurgan

It might be lucrative for your buddy to manufacture a plate to be sold here so this issue is alleviated to some degree? Just sayin'

I was already starting to think about that! I will talk to him and see what he says.

[thekurgan]

Originally Posted by F360C

I was already starting to think about that! I will talk to him and see what he says.

From the photos, looks like a reinforcement plate above and below, longer higher rated bolts would be pretty beefy, assuming the surrounding steel holds up; seems like it would; it's the bolt area that fell apart.

[sabbanick]

Hey this sucks to see and I hope it all works out for you. Just want to say thanks for bringing this potential issue to light for the rest of us who track this car. I obviously couldn't make it the E-town but hope you got my point that is was going to be a last moment decision... Would have been awesome having to gotten some seat time with you though. The time will come when we meet up and it will most likely be at the track.

When the time comes for suspension upgrades, I think i'm going to have to consider getting all the known stress points on the frame properly reinforced. The only thing that scares me is the cause and effect of doing so...

[ryanchua]

I had the same thing happen to me a month ago.

Was running beefed up ground control sway bars and the mount plates gave way pretty much like how it is in your post. Anyway - a guy who did racecars said it was pretty standard for street cars when they're beefed up, and furthermore, it's empty right behind where the bar bolts to the frame. That's a big weak spot - but sufficient for street ARBs.

Not to repeat what others have already said in here, but i did some frame reinforcements and now it's all welded a lot more strongly. I''ll take some photos when i get to my next servicing.

Don't worry - just beef it up more.