shock mount on the trailing arm rusted out.

should i replace the trailing arm, do both anticipating that the other side is ****ed, or is it easier to swap out the whole subframe with the arms attached?

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1984 300CD

I've replaced the left rear trailing arm twice on my 83. Once about 8 years ago due to collapsing from rust, and again this year for shock mount rusted through. Fairly straightforward change, no spring compressor needed, by dropping the subframe. The most difficult part is the ebrake shoes and linkage components. Ironically the passenger side trailing arm is fine.

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Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k

a few questions:

1.) if dropping the subframe, should i replace the subframe mounts?

2.) if dropping the subframe, how much more difficult is it to just replace the subframe and with both trailing arms attached, than a single trailing arm?

3.) is there any other rubber/parts i should have on hand in case they are destroyed or found to be shot in the process?

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1984 300CD

I went through this job this past spring/summer (replaced trailing arm bushings, but not the actual trailing arm). Here's my take:

1) I would consider it, at minimum. Initially, I wasn't going to. The passenger side looked passable. But, the driver side mount broke apart easily by hand when I removed it. So, I was forced to do the job.

Subframe mounts weren't bad once I'd gotten that far. I bought the cheaper mounts (Meyle?) that a lot of people report fitment problems with. I came up with a press tool of my own design for the subframe mounts and inserted them with the help of Sil Glyde. I got them in all the way - perfect fitment.

So, if yours are AT ALL questionable, I'd do the job now. You'll never have better access.


2) I'm of the opinion that replacing the whole subframe with trailing arms would be more difficult and probably unnecessary. Here's my reasoning:

-once you have everything necessary removed/disconnected, and the subframe lowered, then there are only two nuts/bolts on each side holding the trailing arms on. So, by the point you have access to replace a trailing arm, or the whole subframe/trailing arm assembly, you're only two bolts away from replacing a trailing arm.

-in order to replace the subframe, you'd need to wrestle the old one out from under the car and wrestle a new one underneath the car. Also, if you source it yourself from a junkyard, you may need to remove it from the donor car yourself while at the junkyard, and then truck it back to your workspace. That's a lot of work and a lot of moving you may not need to do, on top of the added cost of a lot of other (possibly) unnecessary parts.

3) At minimum, I would replace trailing arm bushings on both sides if you're replacing a trailing arm. (Unless the old ones really have no noticeable wear/play. You may or may not also want to replace the rear differential mount and/or the rubber spring pads/spacers.

I just did this on my 84 SD
I decided to to everything at once, so I dropped the whole subframe
using three jacks: one under the diff and one under each trailing arm.
I got all the rubber parts from the dealer, so, hopefully, I will never
have to do this again.

Good Luck with your project,
Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

Just ordered the subframe mount kit, diff mount, and bushings just in case. Thanks guys.

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1984 300CD

https://www.youtube.com/watch?v=e1QrWRxZtaM

Here's a video on building a tool for your trailing arm bushings.
It worked well for me.

Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end

That's my video. I'm MercedesDieselGuy on Youtube

That being said, here's my video on replacing the subframe mounts with another DIY tool I assembled myself:

https://www.youtube.com/watch?v=f58y0QCV284

MagicBus,
Good info. Thanks for taking the time to make those videos.
Should be a good help to others doing the job.

Jeff
I, too, am fueled by coffee.
I have this friend named Peet..........

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end