W126 300SD Rear Lower Shock Mount Broke!
 

Hey everyone,

Around Christmas time my dad informed me of a rattle in the back end of his 300SD. I chased it down to a sheared off shock bolt. The innermost bolt had sheared off and the shock was only being held on by the one bolt.

I finally got around to taking a more indepth look. I took out the good bolt and went to the hardware store to get replacements. Came back and found that the "good" bolts mount had broken free of the lower control arm.

So now I am looking for options and explanations:

1) I could weld the mount back into the lower control arm and use it.

2) I could replace the lower control arm and go from there.

Explanations:

Why would this happen ?

I think maybe the rear springs are weak/bad?
Force transferred to the shock and sheared the one bolt leaving the "good" one to take the load...and then the control arm metal failed...or something along those lines..

So what do you guys think?

I am sure someone wants to see pictures.

Could be there is some bad design concerning the where the Shocks Mount or rust?

What does a new R Control Arm cost and how much would it change your alignment?

I'll see about snapping some pictures. I am not sure about rust. I felt this area was pretty clean last time I checked it out.

A NEW control arm.. $2,053 via XXXX IF they are even available.

I was able to get a used control arm for my other 300SD locally for $50, i sunk $200 into it via new bushings/bearings and here's the result:

http://www.peachparts.com/shopforum/diesel-discussion/303427-w126-trailing-arm-rear-lower-control-arm-rebuilt-replacement.html

It looks like there was some rust present as well. I surmise that the rust was not AS big as an influence as the sheared bolt on the other side. I couldn't get a good picture of that but the head was completely sheared off forcing all loading to the other side..

http://i.imgur.com/xHBiFl.jpg
http://i.imgur.com/Yslyjl.jpg
http://i.imgur.com/fX30Hl.jpg
http://i.imgur.com/h0enHl.jpg

Weld on a new bolt. I had a shock bolt and a Panhard rod bolt break off on my Wanderlodge (prior to my purchase). I assume it was a big pothole or something. Is there a bump stop missing which allowed inordinate pressure on the shock bolt when hitting a big hole?

I don't believe any of the bump stops are missing. I believe the fact that it only had ONE shock bolt in place cause a lot of pressure to be exerted on the one that broke. My dad travels on some pretty ****ty roads too.

Where would I weld a new bolt in to? Just put metal over the missing section and a bolt on it?

That's what I would do. Much less work than replacing the whole lower control arm and the rest of the arm looks to be fine.

Hmmm do you think my welder would be able to weld the metal adequately so that it was strong?

Here is what I've got...
MIG Welder | MIG Welders | MIG Welding

I used it during the restoration of this car and installed a 1/4" thick piece in place of a jack point...

http://www.peachparts.com/shopforum/2618488-post27.html

Most of the welds on the restoration were either low duty cycle load bearing or non-load bearing...

Probably but I'm not an expert on welders.

rear trailing arms
 

Just so you know, I have shipped those before.... Let me know if you decide to replace because there's a w126 in the boneyard right now.

How bad was shipping? What did they yard want for the part? I don't mind paying so long as it's reasonable.

It's a pretty big box.....but by removing the brake hub and all, I think it's the size and not the weight.

The yard cost is the cheap part....

PM sent

My main concern for welding new metal in there is strength...

1) Can my welder weld at suitably high enough amps/volts to ensure that the metal can endure the forces/duty cycles?

2) Whats the condition of the other bolt's metal surrounding area? It might be weak? Fine?

Ideally what I would like to do is replace:
-the arm with a rust-free arm with new bearing and rubber bits.
-A new swaw bar link
-new springs and spring pads.

The first year after I bought My car I installed a used Trailing Arm and have had no issues with it. It was $125+ shipping.


I actually bought one for each side as both had rusted through spots.
the one I replaced cracked nearly in 2 when I ran over a 3 inch high curb on a traffic island doing 45mph.


The Metal the R Contol Arms is made of is very thin and even less so if it is rusted. That does not bode well for welding.


I think if you are going to attempt a repair you need to make 2 circular Plates (sort of 2 large thick Washers) that fit into the Hole the Shock Absorber goes into and put one Plate on each side of the Control Arm.

That will spread out the stress all over what is left of that sort of flange.


To keep the plates from moving around either JB Weld them to the Arm or Tack Weld them on their inside diameter. I think any welding around the out side would only weaken the Metal.


Instead of attempting to drill and tape for the Bolts simply drill the hole all the way through and use a Nut on the other end of the Bolt.

107 114 115 123 use the same arm.