Pasha Mercedes

Hello! I have replaced the lower control arms on my 07 S550 a couple of years ago. And I still have the old parts (nice and clean). Is there any use of them for anyone? Or should I just put in the a dumpster?

Senecat

Rebuild them and keep as spares.

BOTUS

which - these are both lower arms (as in, at the bottom of the steering knuckle) the black steel track control arms or the aluminium castor control arms

the steel ones you can rescue the boot on the outer ball joint and post to someone fortunate enough to have had the Mercedes dealer make my day trick - where the shop's stab them with a screw driver to get a nice earner
the aluminium ones can have the front bush replaced, but its not that pricey anyway

kevm14

Remind me again what the applications were for steel vs aluminum?

BOTUS

?

aluminum - unsprung weight, easier to make, cheaper
steel - better able to take abuse from the tank above it, kerbing incidents from great drivers

kevm14

I meant what was the rhyme and reason for aluminum vs steel. Which cars have which and why?

BOTUS

that all have both - the upper wish bone is aluminum too - so basically its all aluminum except the bit getting a kicking everyday that bears the vehicle weight

BOTUS

120 aluminum - castor control (maintains the back and forth forces like braking, named after the angle it keeps aka castors on a shopping trolley - helps the wheel go in a straight line)
70 steel - track control (side to side - width - as in track (like a train track)

kevm14

I was under the impression that part 70 is available in both steel and aluminum, which I didn't understand. Is that not correct?

BOTUS

there are different arms depending upon the model

airtragic
ABC
4x4

I think the track control arms are all steel - but there's a passion on this forum to use appalling naming conventions - I try to sway opinion but the ARB seems get them all bitter and twisted

kevm14

I swear I tested mine with a magnet and came to the conclusion that they were not steel....and I thought I saw listings for silver (presumably Al) and black (presumably painted steel). That just seems weird.

Arrie

The rearward load bearing control arm must be much stronger. It carries the weight of the car at the point where the strut connects, i.e. the rearward arm is a bending beam. It also carries axial forces but the bending forces is the reason it needs to be made of steel simply because aluminum is not strong enough. If someone makes this part of aluminum does not understand the requirements and why would anybody do that as aluminum is more expensive than steel.

The forward arm is aluminum as it only carries tension forces so aluminum is strong enough. The reason for using aluminum on all parts where it is possible is to minimize the weight of the suspension parts. More weight means lower natural frequency that hurts the ability for the wheel to maintain road contact on rough road surfaces.