Rusty trailing arm - imminent danger or not?
 

I had my '85 300D in for an alignment recently and the tech said he was having trouble bringing the rear fully into alignment due to rusty trailing arms that he thought might be bent. He recommended replacement of the trailing arms.

I was aware of the trailing arms being a bit rusty, but does it ring true that they might be bent?

Here's a pic of the right trailing arm rust, does this pose an imminent danger or a likelihood of being bent?

https://bn1304files.storage.live.com...OLVM7dP301ZOA0

https://bn1304files.storage.live.com...553.jpg?psid=1

My car does seem to be sagging in the rear a bit, and when looking at it from the rear the tops of the rear tires lean inward ever so slightly. However I've thought this could be due to:

• A few years back I cut half a rung out of the rear springs and swapped in the thinnest spring pads. I did this after rebuilding my front suspension and used KMAC springs in the front which sat a bit lower. At the time the rear seems to sit up to high.
• AFAIK the rear bushings have never been done (car has 310k), so at the least I probably need new subframe bushings and differential mount bushing

I guess my question here is whether the trailing arm(s) really need replacement due to rust, or am I ok to just add subframe bushings, new springs/spring pads, etc... to try to improve the rear alignment?

Change it immediately - the chances are pretty big that it is a lot worse on the inside.

And I'm surprised the tech at the alignment place managed to make adjustments on the rear wheels on this system as you need to remove the trailing arms and put in eccentric bushings - so if he really said he made an adjustment I'd like to know if he was once an understudy for Uri Geller...

X2!!!!!!!!!!!!!!!!!! DO NOT drive on that anymore, its an accident waiting to happen....

Yup... find a better one. The uni body design of it doesn't cope well with rust.

Yeah you better just part the car for a while till you replace the arm or both arms.
They are just two pieces of stamped sheet metal welded together.
It`s not the rust you see, but what lurks inside.
You may get 500 miles or 5 miles before it suddenly becomes a danger to you and every one around you.

It can lead to this.
http://www.peachparts.com/shopforum/...oke-arm640.jpg

Or this
Rear Left Trailing Arm Has Cancer - Mercedes-Benz Forum


Charlie

sent from my pos computer

Naaaah, that'll buff out.....

just kidding.;)

Charlie means, "PARK the car" not "PART the car" I believe. Of course I could be wrong and he is looking for some parts for his ride.:D

Yes those trailing arms or at least one is very,very weak I think. I would inspect the whole lower chassis for any other problamatic areas as well.

Hope it is only the trailing arms and may just be. I would not drive on them either.

Well, that was a unanimous round of responses. Looks like I will be replacing my trailing arm(s).

The rest of the car's underside looks good. My axle boots are worn but not cracked yet. I live in Seattle, but I bought the car from Nebraska and I believe it was previously somewhere on the east coast.

Anyone have some good trailing arms for sale :)

Also, would it be easier to just drop the entire sub-frame and replace while off the car, or swap them out one side at a time? I'm leaning toward the former since I need to do the sub-frame bushings and other bushings and possibly the axles as well. On the other hand if it is as dire as it sounds maybe I should swap in a new arm asap and work on the bushings and other replacements at a later date.

Once she's up on stands it's not too terrible with a big breaker bar. Make sure it's on level ground before you start :)

Sorry, do you mean for swapping in a new arm without removing the subframe, or dropping the entire subframe and replacing with the subframe off the car?

I replaced a trailing arm for same reason, '85 wagon, and my car had lived in the rust belt too long so the job was very tough. I had access to a very nice lift for that job, and also a "blue wrench" aka oxy-acetelene torch, and it was two hard days of work, 8 hours each day. In my case I did what you're thinking about, I did ALL the rubber while I had the rear end apart. I also replaced both supply and return fuel lines, as one of those was rusted and starting to weep.

If your car is not too rusty, and you've got prior experience with pulling out and pushing in new bushings, I'd plan on one long day of work.

As a voice of dissent, my 240D had a 3" crack near the axle end of trailing arm when I bought it in 2007, and I had a friend weld it to repair it in 2014, because the edges were rusting. I'd check it with a hammer or screwdriver and see how much material has rusted away and where. Why not weld or braze a patch on?

It'd be a tricky patch since the shape of the damaged metal is a double curve, and it is thin metal so it requires the correct equipment and a skilled welder. Finally with the inside not visible it is hard to tell how much of the part is damaged inside where it is invisible.

But yes, if you could find the right person a patch would work.