mwood95
mwood95 New Reader
8/13/22 3:58 p.m.

I am in the process of making an '02 mercedes c class handle. as some of you may be aware, the w203 c class uses a unique, fixed upper strut mount that prevents camber adjustment. you can buy expensive adjustable bushing kits for the LCA but Im not sure they have enough adjustment to really fix the car's issues.

as it stands the car is really predictable and rotates well but has persistent understeer and is wearing the front tires really unevenly. i almost destroyed the front outer sidewalls at an autocross and ended up rotating them to the rear, which has correct camber after fitting lowering springs.

i picked up a set of adjustable lower control arms from a seller on ebay to try them out and see if a longer arm could create negative camber without ruining the suspension geometry etc

upon installing them i was a little alarmed by how far out i had to unthread the adjustment barrel on the LCA to get a lower arm that was just .5" longer than the stock LCA. I ended up with a couple degrees of neg camber but i am a little concerned about the safety of running the new LCA at this length. 

 

for reference there is about .8" of the threaded adjuster tube inside the control arm (not counting the width of the lock nut) and about .6" of the shank of the heim joint inside the adjuster barrel (again not counting the width of the locknut)

 

i am wondering if anyone with more engineering saavy than I can advise how dangerous this is, how likely it is to bend or snap somewhere etc.

a possible solution is to have a machine shop turn me some longer adjuster barrels. as it stands if this setup is safe, the car finally has the front suspension geometry i want.

best

Mitch

Asphalt_Gundam
Asphalt_Gundam Reader
8/16/22 2:46 p.m.

IMO that's super sketchy...what's with the double threaded end?

Rule of thumb is a minimum thread depth that is the diameter of the threads....however I wouldn't be comfortable with anything less than 3/4" dia thread and more like 1" of engagement.

That lower arm looks dead simple. I wouldn't think twice about a chrome-moly rod end and fabricating the proper length from DOM tubing. As the offset looks minimal you might be able to even get away with just two rod ends, spacers, and a strait tube.

mwood95
mwood95 New Reader
8/16/22 3:30 p.m.

In reply to Asphalt_Gundam :

thanks for the reply, I feel the same way.

the adjustment barrel is threaded RH internally and LH externally so that you can adjust the arm length without removing the arm. here is an example of some datsun control arms that are the same way:

 

you can see how far they are comfortable running their adjusters in that photo. I might email them to ask how much shank they require to be threaded into the arm for both the adjuster and the heim joint.

yeah I wish I still had space to do fab projects like this i could have easily made some longer arms but Im living the apartment life these days.

best,

Mitch

jfryjfry
jfryjfry SuperDork
8/17/22 8:52 p.m.

I bet you could extend the arm by 1" or maybe more to get it where you want it.  Either have a new curved tube made and replace (cut and weld) the existing one or cut and sleeve what you have.  You could do an inside tube and then an outer sleeve. 

Purple Frog (Forum Supporter)
Purple Frog (Forum Supporter) HalfDork
8/17/22 9:22 p.m.

I didn't stay in a Holiday Inn last night... but...

My understanding is the most force on those pieces under different cornering loads would be in compression...(trying to push them together, not apart), so what you have is probably fine as there are more than three threads in each fitting.

YMMV

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) UltraDork
8/27/22 2:04 p.m.

I saw this a few days ago...  these looked scarier to me.

preach (dudeist priest)
preach (dudeist priest) SuperDork
8/27/22 2:26 p.m.

In reply to mwood95 :

No, just no.

Imagine the damage to your car when that comes apart.

Additionally I drive on public roads.

Nockenwelle
Nockenwelle New Reader
9/3/22 1:41 p.m.

As someone who gets paid for making structural engineering decisions for aerospace, I don't like it. It's not only the adjuster thread engagement: the geometry makes for some weird loading, and quite frankly there is the high probability of poor-quality components and metallurgy as an ebay special. You would do much better to make your own as Asphalt_Gundam suggested with LH/RH rod ends and a piece of straight tube. You could probably buy Aurora ends, the steel pieces, and a stack of spacers for the pivots, then pay a competent TIG-wielding friend to melt them together and have a better solution for about the same cost.

Our Preferred Partners
vM9eXs37OWBjUs6VyuqGgW1RZ4GcPlex9cTT5k9kOjZ4Tr4ovt16PpLZR5uXTCwS