Rear Crossmember.

[FluxMorz]

So, I may have bought a dud.

I briefly mentioned in my introduction that my 1998 Z3 M44 was being repaired for a problem in the rear that was causing excessive wear on my tyres. Down to the wire (literally) in 6000kms. I've had the car 5 months, this happened in 4-4.5 months.

The tyre place who I initially went back to with the complaint said that whoever had lowered my back end may not have made the correct adjustments to account for it, /or/ that I might have rear tow damage. They recommended a suspension shop to me.

The suspension shop tells me I have a bent rear cross member. They say to have it replaced brand new, with labor would cost $3,500AUD. f***. They also say that buying a second hand one is risky because you can easily be purchasing another bent one. Looking around other forums, this seems to be the consensus too.

So, rather than this being a sad rant, I guess what I am asking is the following: Is a bent rear cross member something that can be visibly diagnosed? Is it something that is easy to fix yourself, if you have a healthy replacement part? And how difficult would it be to reliably purchase a second hand?

Thanks in advance guys...

Oh, one last thing. I did a check on the car before I bought it and came up with no reported issues...

 

[zedonist]

The Z3 has no rear camber adjustment, therefore when you lower it you get negative camber as part of the process, how much depends on how low you have gone, the result is excessive tyre wear to the inner 1/3 of the tyre, the rate of wear is again dependant on how low you have gone. If you have consistent inner edge wear on both tyres I would say the chances of a bent cross member are nil, I would also argue that if you actually have a bent cross member, then the car was most likely in a very serious accident, as the cross member is a very heavy load bearing structural arrangement.

If I was you I would go look see the bent cross member, because if it is not bent, fitting a new or old one will give you the same issue, the only way to remedy the situation is to fit original springs, or have a camber adjustment kit welded on. If you want it lowered and can live with some tyre wear, then don't go no lower than 30mm.

 

[roadvoyager1]

Your post sparked my interest. I am fairly new to the Z3 and had not looked at this area before.

Had a look on RealOEM to find the cross member.

If it is the part numbered 1 in the diagram (Rear axle carrier), something pretty serious has happened to your car in the past and IMHO there is very likely other damage to the remainder of the suspension. If by cross member you mean the actual beam that is spot welded as part of the body structure then something very serious has been going on and the damage may well be beyond cost effective repair. On the brighter side if you decide the car is a dud, breaking it for spares may well give you a good start on the funds for a replacement (think 6 cylinder or even Z3M?).

I am sure others who are more familiar with the Z3 suspension will give good guidance on the best way to proceed.

 

[Aceman]

I think zedonist has hit it on the head really in that if you are just getting uneven wear on one side than yes you more than likely have got a problem with the geometry of the rear suspension probably due to being hit hard on one side. However if the car is lowered and you are getting excessive inside wear across the two rear tyres then I would suspect it is lowered too much. Realistically as zedonist says 30mm is the lowest you can drop the rear without getting excessive inner edge wear on the rear tyres. This could turn out to be a relatively easy fix with replacing the springs with either standard or lesser drop springs.

There is also one thing you could do and that is if your rear subframe is indeed damaged you could look into doing a widebody converion if you can find a 2.8 at a breakers yard to act as a donor vehicle.

 

[FluxMorz]

They said it is 23mm out, and the wear is across both tyres. To reiterate, it was only 6000 kms (4 months) from brand spanking new tyres to one of them blowing out (on the way to get them replaced and the problem looked at) and the other being down to the wire. I will definitely be looking into getting the car raised again to standard. I don't know how far lowered it is.

I'm getting the feeling it has been in an accident and they've done this lowering to try and cover their tracks. Or something to that effect. But when I paid for the basic insurance/money owing report it came up clean...

I have some mechanically minded friends who are used to customizing and maintaining cars for performance, and I have a M42 318is enthusiast friend and maybe Cooper too if he is keen, who are willing to take a look and help out with doing the replacement if I can get a hold of the part (seems doable). The tyre guys are the ones who took a look and said its out by 23mm, and said it could be rear tow, and it is the suspension specialists who are saying the cross member is bent. And both parties asked if it had been in an accident.

Do you think I'm being taken for a ride, and its something less serious, or do you think I'm in trouble here?

Side note: Even if I was to dissect the car and sell it as parts, I'd be recovering (at absolutely best) enough to buy another car of equal value, surely - especially since my area is so small, and the car is so uncommon - and would in no way be able to get a Z3m ($32,000 AUD imported roughly). And it wouldn't be a chance for a wide body conversion either, as that's extra money I still don't have. I'm dipping back into my loan to pay for all this as is.

 

[FluxMorz]

Also, just really quick, they haven't mentioned any other damage in the subframe or suspension areas so I can only assume they believe there is none? They're 'specialists' after all, or should I be looking further into that too?

Oh, and when I got the car we had to get under it and fix a wonky gear-shift that was sitting slightly angled to the left (right hand drive car) so I don't know if that was also part of the same potential accident but it was easy fixed.

 

[t-tony]

I would be very surprised if your x-member is bent bud, I've just had my car on the ramp at work and looked. If it had been in an impact big enough to bend that lump it is I unlikely that it would have been repaired by an insurer.
23mm out is "only" 11.5mm each side which is more than likely caused by being lowered too much, measure your ride height and ask a forum member with standard suspension set up to measure theirs and then you can compare and know how lowered yours is.
Above all don't despair, things are rarely as bad as they look, because if both tyres are wearing that alone points to lowering as the cause of your problems.

Chin up we'll get to the bottom of it, cheers Tony.

 

[Cooper]

I suspect lowering is your only problem as this accounts for the wear on both tires, inside. The other guys will be asking you about accidents because they may not be aware of the lowering that has occurred. Try not to worry about spending lots of money and such. Someone will be able to provide some indication on the proper heights ground to xxxx and such and we will measure it. I can also bring my Zed around and we can take some measurements from that. I don't know how [or if] the cross-member can be surveyed for damage without specialist tools. Let's get some more information and then take measurements, then worry about $. I hoisted my car today and it is in 'as new' condition and you can always take your car to that mechanic just across the bridge - it cost me $35 for over half an hour's inspection! I can bring my car down there at the same time to compare.

 

[t-tony]

If you do get under the car to have a look Coops check specifically for cracked paint new or old that show rust weeping out of the cracks in the paint. Also compare measurements from one side of the car to the other. These are the first things I look for when a customer comes in and admits to heavy impact on kerbs or whatever.
Best of luck,Tony.

 

[FluxMorz]

Thanks for that Cooper and t-tony, we'll definitely have to get together and have a chat about this. I recommend my father's house as he's relatively mechanically minded and with me being a total noob, the two of you would probably be able to work out some form of method of attack.

 

[t-tony]

TBH you'll have it sorted by the time I could get there. What they refer to are toe arms mate not "tow" arms. We would probably call these track control arms which maintain the wheels, front or rear, are pointing in a straight line give or tale a few mm.

 

[zedonist]

When measuring height the passenger side sits higher due to the fuel tank shape. I will look up the TIS information for rife height but it will be for a standard car not lowered.

 

[zedonist]

Here is the data:

BMW TIS online
Technical and background information on vehicles BMW and Mini
33 00 Rear axle - ride height E36 / Z3

normal height position (measured from the lower tape edge of the wheel rim to the bottom edge of the wheel housing on the axis passing through the center of the wheel, y Z3 - up devices)
The difference in deviation from the preset values between all wheelsmax. mm10
serially
Rim 15 'mm B565
Rim 16 'mm B578
rim 17 "mm B593
Roadster M: 588
Sports suspension, low-slung chassis and M
Rim 15 'mm B550
Rim 16 'mm B563
rim 17 "mm B578
Rough road
Rim 15 'mm B
Rim 16 'mm B
rim 17 "mm B

 

[vintage42]

"The suspension shop tells me I have a bent rear cross member."
The cross member i.e. differential carrier looks impossibly strong to bend or damage. I can't image how such force could be applied to it without being transferred into its three mounting points and damaging them -- the two end bushings and the differential bushing. Look at the mounts for those bushings.

 

[roadvoyager1]

Completly agree with vintage42. Lets hope that your checks confirm that it is just excessively lowered and can be sorted without too much expense for you.

 

[FluxMorz]

Thanks a lot for the help guys, I really appreciate it. I'll be bringing it home asap to see what we can discover. I'm a little worried that we may be under-qualified to assess this all but we'll see how we go.

 

[Dino D]

My 2.8 is lowered and wears the inner edges out much quicker.
Every BMW I have had did this, lowered or not as they all have some camber at the rear. Plenty of other brands do it too.

I only get 10k miles on the rear (16,000 km) and that is by swapping the tyres from side to side (so have to be removed from the rims and swapped over to keep the direction of the tread correct).
Cheap and quick to do and doubles the life of my tyres.

Any pics if the car to see how low it is?
How hard do you drive it? The harder you accelerate the more the rear squats and causes the inside to wear on these cars.

What brand of tyres?
Very soft brands would wear faster.

I doubt the cars a dud based in what you have said given my own experience (and seeing plenty of other BMW's tyre wear patterns).
The 'wonky' shift is also a common thing I believe.
There are plenty of quirks to these old cars now which some 'modern' mechanics may not recognize and just says it's knackered and needs replacing!

 

[zedonist]

Bang on Dino, because of the structural nature of the rear beam, if it was twisted there would be obvious body repair visible.

Can I suggests flux that you take a few pictures from the rear and sides and post them, Aldo dome pics of the wear pattern on the tyres, this will help us to be diffinitive in an answer.

 

[oldcarman]

If that rear carrier was cranked that hard wouldn't the mounts have snapped off and bent up the boot. Pull the carpets out and have a look for damage repair, it's hard to hide in that area. JIM

 

[FluxMorz]

I'm getting my car back today, and we'll take a look under it before we bring it back so I'll have some sort of update soon.