I looked in the archives and couldn't find a definitive answer. Are the upper and lower control arms swappable? I bent my upper control arm when I whacked a guardrail last weekend-- understeer + decreasing radius turn. The rest of my rear suspension looks okay. If the upper and lower control arms are the same, then I'll buy adjustable control arms to replace the lower control arms and replace the bent upper control arm with one of the lower arms.

 

They're the same part for 1st gen MINIs, but different part numbers for
gen 2 MINIs.
Your 08 MCS Convertible should be an R52 (1st gen), so they're the same.
http://www.realoem.com/bmw/showparts...27&hg=33&fg=30

 

Interestingly, RealOEM shows different parts numbers for the top and lower Control Arms (wishbones).
Top Wishbone 33326768724
Lower Wishbone 33326768726
I am not sure what the difference actually is unless it has to do with the adjustability of the lower control arm. Maybe the hole is slightly different to accept the adjusting plate (Item #15).

 

The driver's side is definitely different since the upper control arm has a couple of holes for the HID leveling sensor. But the passenger side doesn't have that. There is a bump stop on the upper arm, but it seems there is a hole to accept that on the lower arm as well. I guess I'll have to take it apart and compare the two to make sure.

 

Oops. I missed that. In fact the uppers are black and the lowers are grey.

 

I looked up the prices and they're priced differently too. The lower ($165) is more expensive than the upper ($138).

 

FWIW,I could swear i read that if you were planning on buying aftermarket arms (helix,etc..) you could buy 4 (all the same) and adjust camber with the upper and toe with the lower.Not sure this applies to oem as they are not adjustable,but it looks as though the mounting brackets must be the same (upper and lower) if they both accept the same aftermarket arms.My $.02

 

Yeah, you can buy 4 identical aftermarket arms to replace the OEM arms. The thing is the OEM part numbers are different and so is the price. I'm wondering whether they are slightly different lengths which wouldn't be a problem with adjustable aftermarket arms, but would be with non-adjustable OE arms. BTW, based on what happened to my suspension, I tend to think that they OE arms are engineered to give before the other parts. The arms are one of the cheaper, easier fixes and it clearly crumpled to take the impact. None of the other suspension parts were damaged. This might be another argument for keeping the upper arms OE.

 

i remember from one of meb's posts about adjusting toe is you don't adjust toe with the lower control arm, only camber. what do you get to adjust when you replace the upper control arm?

 

Yes, Meb has stated that toe should be adjusted with the trailing arm not the control arms. Camber is mainly adjusted with lower control arms. However, if you have adjustable lower and upper arms, you can adjust camber and track width (by adjusting both upper and lower in/out the same amount). I believe that you can adjust toe with the upper control arm but it is difficult (not the best way) because you also change the camber so it becomes a big trial and error task to get the camber and toe set correctly using only the control arms.

I think even the aftermarket adjustable arms are still the weak leak in the rear suspension and still bend before other parts. At least, my H-Sport control arms bent without other suspension pieces bending (other than maybe the strut, not sure about strut because car was totaled) when I crashed my MCS into a curb.

 

Mystery solved. I removed the upper and lower control arms and they are the same dimensions in every way. However, there are two differences. The lower one is silver and appears to have a heavier finish (probably because it is more exposed to the elements) and the upper one is painted black. And the upper one has 2 holes on each side to accommodate the level sensor on the driver's side upper control arm. Since the one I bent is on the passenger side upper, I simply swapped the upper and the lower and I will order adjustable arms to replace the lowers on both sides.

 

I was told the bottom arms are finished - galvanized? - to protect these from the elements.

All four are interchangable, unless you like your headlights to level

 

Yep, they look galvanized. Apparently, that costs an extra $30.