Fixing an "upper control arm" thunk

When my local MB mechanic replaced all the lower front end suspension parts on my 79 280CE and I picked up the car, he said: "There is some clunking remaining, but it isn't in the suspension. You have old non-original shocks, and my experience is that with any brand other than OEM/Bilsteins, front end rattles can happen. OK, a few days ago, I put new Bilstein comforts on the front, and while some very minor rattles cleared up and the car is a bit smoother at highway speed; one clunk got much worse. It is a loud clunk that only happens while going over bumps during low speed turns. I had a friend listen while I bounced the left front end up and down, and we detected the noise seeming to come from the outer end of the left side upper control arm in the joint that connects to the rod coming up from the wheel. Question: Is this a bushing replacement? Easy to do? Or am I looking at more major surgery? The car is in another's shop this AM for an adjustment to the alignment that was done after the new suspension parts, and I want to call them off if I'm wasting my time on an alignment before the thunk is fixed. Advice?

PM.
The shop didn't do what I asked and just called saying the alignment was done. In the process of discussing the thunk, they called the parts other names than I was using based on descriptions in a Chilton Manual. Since Chilton has been wrong as much as right, that could be why no one has responded to my note. The shop said the fix was $250 which I assume is both sides, but what I really need to know is whether this is an easy enough fix to try myself. Let me try a more generic explanation. Looking up and into the front wheelwell, directly above and behind the tire, there is a knuckle joint that connects to a short cast iron arm coming out of the inner fender and to another rod that extends rearward before disappearing into a hole in the top rear of the wheelwell. The rod up from the axle bolts to the bottom of this joint/knuckle, and it appears that the bushing surrounding the bolt has failed allowing the bolt to shift and transmit a thunk through the car. Is this a simple unbolt/stick in new bushing process? Or does the entire arm up from the axle/wheel and inside which rides the bolt/bushing have to be replaced? Help?

[psfred]

The W123 (and the W116 and W126) has a combination swaybar/upper control arm, and yes, the bushing is bad on the driver's side at least. Probably both.

This can be done, but it's a pain in the backside. You must get the top ball joint apart without breaking anything, and you then have to remove the sway bar to get the mounts off. I don't believe it has to come all the way out, I've not done one, but you will wrestle and swear some.

There are a couple of post on this, try a search and see if you can get a good description.

Peter

Originally posted by psfred
You must get the top ball joint apart without breaking anything, and you then have to remove the sway bar to get the mounts off. I don't believe it has to come all the way out, I've not done one, but you will wrestle and swear some.
Peter

Peter, I couldn't come up with a search that revealed anything helpful. Re your quote above, top ball joint apart without breaking anything? Do you mean just getting the nut on the bottom of the joint loose? With the car on the floor I couldn't get it to move, but think with the car up in the air and the tire off for some added leverage it should come free. What might I break?

Is the sway bar the name for the piece the bushing is inside of and which is connected on the other end down to the axle? Otherwise you lost me in the description.

[psfred]

The upper control arm is quite small -- the sway bar (the part that looks like the upper control arm) goes through a couple of bushings on the firewall inside the engine compartment and acts as the control arm.

The bolt that holds the control arm to the sway bar can be a problem -- the end of the sway bar can crack. It is also in an awkward position to use a ball joint tool on, and you must take care not to tear the boot, else you will be replacing it shortly, it gets quite a bit of road dirt thrown on it.

You will also have to wrestle the sway bar around enough to slide the bushings out to replace them. It won't pull straight out, alas.

Just a hassle, not hard.

Peter

I'll bet Mercedes terminology confuses the heck out of a lot of folks. My Chilton manual calls the parts one thing, the mechanic who did the alignment another, and last nite on the way home I stopped at my regular Benz wrench to talk to the guy who rebuilt the lower suspension and he called the parts something else.

Of course I could not replicate the thunk when the mechanic was standing there, but his "fix" is to replace the part that includes the knuckle/upper ball joint which he calls the upper control arm. The part that bolts to this knuckle/ball joint that comes up from the axle, this guy calls the wishbone.

His opinion is that the thunk is the knuckle failing and said he'd replace this one side for $200....that the connection to the knuckle is under tension from the coil spring, and isn't a job to be tackled without some expertise.

This is conflicting advice, so I'll do some more investigating and advise what I find out.

[psfred]

The upper control arm won't be under spring tension with both front wheels off the ground! We didn't have any trouble taking the steering knuckle off (not the wishbone, the W126 doesn't have one) including taking the upper control arm loose.

Not a bad job if you have a couple jack stands and a floor jack.

$200 is pretty steep for that, IMHO.

Peter