Is W123 300D LCA failure likely?
 

Dear All,

I'm slowly getting my front suspension back on my 1981 W123 300D. But before I reassemble the bits I wanted to check to see if anyone had ever heard of lower control arm (LCA) failures? I'm guessing with a heavier diesel engine these components suffer the most...

The existing parts were covered in surface rust that fell off with a vigorous brush from a wire brush. It was a bit like removing welding slag. The rust was probably at worst about 1mm thick.

http://www.peachparts.com/shopforum/...pictureid=2251

They seem to be fine as they ring nicely when tapped - so there is no obvious sign of cracking. I'm 99% sure they are fine but I thought I'd check.

Here's a picture of them now during their rust treatment phase

http://www.peachparts.com/shopforum/...pictureid=2252

Thanks in advance for any tips and advice you can give.

I actually ran into a 3-1/2 inch tall Traffic Island on the Drivers side and it did no damage at all to my Lower Control arm. The force was enought that it dented bot sides of the Front Wheel Rims, nearly tore my Rear Traliling Arm in half and Bent up the Rear Wheel.
After replacing the no good Wheels and broken Trailing Arm the Car functioned normally; no Steering Problems, no uneven Tire Wear Issues. So I concluded that the Lower Control arms were not bent or otherwise damaged.
A year later my Lower Control Arm Bushings rotted out and they needed replacement; but even the old Busings survived the Impact with the Island.

I have never read on any of the forums where a Lower Control Arm broke. And, I assume since mine survived a hard impact that they are extremely tough.

Possibly cast steel and pretty tough. It is fair to say they may be even overbuilt. Remember most lower control arms have just been pressed sheet metal for years now and really prone to rust.

There is a video where a W123 flies over a hill and hits the ground from about 3-4 feet in the air at high speed....didn't even flinch. MB suspensions are built to military standards. :eek: A lower control arm will never fail, the ball joint can, thats about it.

Not likely to fail. A LCA could support several 10's of tons of weight. The ball joint & mounting on the body will fail long before the LCA. It is designed to have a very long fatigue life. Best you paint it with a good quality paint like a bitumen based product, replace the ball joint & rubber bush & enjoy a sound & safe front suspension.

Not in our lifte time. Maybe in "Life After People".

The fact that it is round makes a huge difference. This "was" in a time when most cars that were using control arms used components that were stamped and then welded together. The arm itself is stronger than most of the other parts in and around the car.

Wow thanks for the great responses - I'm glad to have had my 1% of doubt put to rest!

For painting them up and making them look good I was planning to use KBS rust seal and their chassis top coat. They say it has a bit of flex in it which hopefully will mean it won't crack and fall off too quickly.

Does anyone have any tips for the mounting surfaces of the bushings? Should I paint these bits too - or should I leave well alone?

I would leave any bushing area au-natural.

OK!
 

OK thanks - will do

for a 30 year old car that has the original bushings on the lca's they are probably shot. your lca's are coated in rust. you can buy new bushings and pay a machine shop $50 to press them in on both sides, or you can do the smart thing and buy new lca's with brand new bushings, and have a mechanic replace them or do it yourself if you have the right compression. kill two birds with one stone, for cheaper in $ and time than painting over old stuff and being stuck with 30 year old bushings.

just sayin

yeah the failure area Id expect is a bushing so rotted that the rest of the part ended up sitting crooked and bending bolts/sleeves/marring up the bore where the bushing sits, etc.

interestingly enough...
 

I believe the lca's are forged. I saw a 300cd which the owner told me he hit a curb that led to the compression/strut rod being bent like a pretzel and it appeared to have put a bit of a twist and slight bend in the lca. Had it been a cast piece, I believe it would have cracked and/or broke. I wish I had had a camera and taken a picture for posterity's sake and this thread's! The tie rods on that side were bent and the coil spring had a rearward "bend" to it also yet there appeared to be no other damage what so ever. You don't even need to wonder about the wheel! For all practical appereances, just the parts replaced and the car would be good to go! BTW, pricing a set of bushings vs. a completely new lca w/bushings pre-installed, well it seems like a no brainer to me which makes the most economic sense considering that the lca is probably a forged piece (and also judging by the price of the new one too!). Pricing the going labor rates for a professional mechanic to do it, well again, if you got some gumption to diy, its like gettting a whole 'nother payday for a weekend's effort vs. setting in front of the boobtube swilling back suds!

sooo..."Git 'er done!"

p.s. for further proof that the lca's are forged, look at the picutres if you can't look at some on your own car, there is "a wide parting line" running pretty evenly the entire length of the part, this is always a sure fire indication of a forging. Castings will have a very fine line which will often have some sharp edged flashing often sharp enough to cut yourself on, and some bit of "offset" where the molds didn't quite line up perfectly

I too think the LCA is forged - I also think the axle shafts are forged but that's another discussion!

It's a shame you didn't get a picture of the bent accident damaged LCA - that to my mind would be all the proof you need 'cos as you say a casting wouldn't be able to do yoga like that.

Here's a continuation of the refurbishment

http://www.peachparts.com/shopforum/showthread.php?t=277850

This is for fitting W123 bushings - apparently the W126 ones are easier to do as come with pre-formed ends... uhm please do a search for this before you believe it!

missed photo op
 

yeah, it never occured to me that the topic would be all that terribly interesting. Believe it, it was bent and twisted, okay?! ;) And so in short, do you need to worry about or should you worry about lca failure, I'd say "Not", not under normal intended use


hmmm, yeah, I'd take that bet, I'd bet the axles are forged also, no doubt.

The rear LCAs on some cars were cast aluminum. The manual mentions it, in the rear suspension section -- there are measurements for checking the stamped steel ones for deformation, then a note that the cast ones will not deform without fracturing and any misalignment is due to the mount points being bent. They recommend replacing LCAs hit hard enough to do that kind of damage, in order to protect against cracking.