Bent trailing arm - how to measure?
 

A few days ago I finished swapping an entire M Roadster rear suspension (trailing arms, subframe, differential, axles, brakes, swaybar, etc) into my 1998 318ti. I bought the suspension complete on eBay and it was supposed to have been in great condition. Visually, it looked fine but as soon as I bolted on a wheel I knew something was wrong. When I lowered the car onto the ground, this is how it looked:

Lots of negative camber:
http://www.strictlyeta.net/pictures/...bad_camber.jpg

Lots of toe out:
http://www.strictlyeta.net/pictures/...and_toe_02.jpg

http://www.strictlyeta.net/pictures/...and_toe_03.jpg

http://www.strictlyeta.net/pictures/...and_toe_04.jpg

Negative caster:
http://www.strictlyeta.net/pictures/...bad_caster.jpg

Clearly, the car that it came from was involved in an accident. There is no adjustment in the rear for camber. caster, or toe, yet they are so visibly off that anyone can tell the parts are damaged. A quick call to my mechanic confirmed, and he's said that this is fairly common with Z3s involved with mild accidents (like spinning into a curb) and both the trailing arm and subframe should be replaced.

I drove the car and it's downright scary - any speed over 25 mph and the slightest twitch of the steering wheel results in wild oversteer.

I would like to take measurements to show that the trailing arm (and possibly subframe) is bent, but the question is how? What are acceptable, static points that I can use between left and right sides? Also, does anyone have any specs from the factory? Any help would be greatly appreciated, cause right now I'm out 5 days of my time and well over $1,500.

Thanks,
Fred

Wow that sucks, contact the seller!. I bought a mz3 rear end myself, but have yet to install it. Did you notice anything wrong at all? Mine has bushings kinda squished out.. And did you notice any changes bolting it in? Perhaps you can use your old subframe, but I would be scared the trailing arm could be bent..

How about some under car pics, like at the swing arm pickup up points. Curious to see if everything was installed properly. Since you have the same camber/toe issue, hitting a curb on one side of the car wouldn't cause damage on both.

I would look to an installation problem before assuming the parts are damaged.

Once you know everything is installed right, you can easily pull the arms and compare them to one another. If they are damaged, they shouldn't be symmetrical to each other.

I would also inspect the subframe completely before assuming it has to be replaced.

You shouldve taken it to an alignment shop before installing the parts, to see how far out of spec your rear is to begin with, then another print out after the installation of your new parts, which would definately show damage on an alignment spec sheet. Take it to a shop and have the alignment spec printed, its usually free, as there is no alignment taken place, just specs check.

If I was diving in to this project, I'd install the adjustment kit while I had the whole assembly out. Yea its some extra $$ but it makes the future adjustment and maintenance so much easier...

You should be able to pick some common points and use a tape measure to check for consistency between left and right, think triangles.

Camber off is likely springs, toe is likely a bent arm or incorrectly installed bushing.

Dave

Thanks all, the seller and I agreed to a resolution.

Bluebimma: The car was aligned less than 3 months ago, and besides, the pictures were good enough for everyone (including the seller and my alignment shop) to realize that something was really out of wack.

mohaughn: The install is correct, there are only two nuts that hold it together. :) I received the parts as one unit (everything from the M Roadster was bolted together and was removed from the car without piece-by-piece disassembly) and both the seller and I verified that it came correctly.

I just didn't want to pull the arms out to compare side by side because it's a pain.

Junk: Honestly I didn't notice anything unusual when I installed the rear end. It all bolted up correctly without any hassle (except for the metal brake lines and the spare tire no longer fits correctly because of the massive differential).

I'm going to go out on a limb here and say since you came to an agreement with the seller than they knew the car it came from had some rear end damage?

You will get negative camber and toe out from dropping the rear of the car. My rear toe is whacked, not the same from side to side, and the arms are perfect. Mostly has to do with the amount of drop.

arm bent out of spec
 

I have rear e30 arm tooling & fixtures LH& RH that we used to build custom fabricated 4130 tubular adjustable R. arms from scratch
could be used to re jig / straighten factory arms also have R lower beam fixture to locate pick up points MASON ENG. fab shop hourly rate is $125.00

My Ti has the same problem but I jumped a curb with it. Don't ask why. The top of the rim is bent in but not as much as yours. Been driving it like that for 2 years and my tires wear evenly and its never gave me any problems. That's why I never did anything about it.

One step at a time...
 

You can purchase the single arm new, which is what I would suggest at this point- if the sub frame is bad, you can get that later and it won't be any cheaper one piece at a time vs. all at once.

If you don't have a BMW CCA membership, get one first. Even only 10% off will save a few bucks on this repair.

Once the new arm is in, see how things shake out. It may be in spec. If it is not (but close) get the offset bushings (factory part as well) and see if it can be dialed out.

If that fails, THEN you can get the sub frame and install that. Doing it this way, you have the least out of pocket at a time, and you will get progressively closer to 'perfection' as you go. I suspect just replacing the arm alone will get you 90+% there- at least close enough to safely drive the car at reasonable speeds. It takes a pretty hard hit to bend the sub frame far enough to be WAY out. Particularly in light of the fact that the sub frame did bolt into the car with no alignment issues, it is probably not bent very much, if at all.

How hard is it to replace the trailing arm anyway? I have to replace mine at some point in time but it is still driveable but I need to replace hubs/bearings and I figure I should replace the arm before I do the bearings. Just in case I found a used arm on ebay and I hope that it isn't b0rked as well. If so, meh...