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

No problem. I'm video-blogging the project as it is. It made sense to make these two parts DIY. I haven't done much of any of that with this project as those kinds of videos take a lot more forethought and setup. I'm over 3.5 years into the project as of now. I don't need any unnecessary delays as I get closer to driving it

If you remove the entire subframe, trailing arms, diff & axles
you will have to have your jack stands to the side of the car.
They will be in the way if you put them under the usual jack points.

I used 3/4 bar stock from Lowes. I put the entire bar in the jack hole
then, using a floor jack on the very end of the bar I jacked up until the bar
got a slight bend. Turn the bar around and slightly bend the other end.
The bend is needed because of the angle of the jack hole. I wanted
the bar to lay flat on the jack stand. Then cut the bar in half and you
have two bars for your jack holes.

I had my smaller jack stands under the car forward of the subframe
as backup stands.

This setup was recommended and is used by WHunter & Charmalu.
I think Charlie put tires under his car as the backup.
Whatever you do, be safe and use common sense!

Jeff

Attached Thumbnails

   

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

Rooster300SD - I wonder if there's a W123/W126 difference here...


I did the entire job with my jack stands under the jack points (1983 240D). They weren't in the way of the job. Granted - this is how I did the job. Apologies in advance for the long, rambling tale:

I didn't know the extent of the work that I needed to do. I just knew that my car needed a lot of underbody attention. I needed to pull the driveshaft to replace the clutch (nearly dead) and driveshaft center bearing (upon inspection, nearly seized, and the mount was destroyed). I couldn't get my driveshaft to compress on the splines (seized) so I ended up dropping my differential and pulling the driveshaft out the rear in one piece and then freeing it up/replacing parts with it on the garage floor.

As others have stated, once the differential mount was disconnected from the body and the rear shocks were removed, the rear springs pretty much just fell out. I wouldn't have believed it, but there is zero tension on those springs once the shocks are out and the differential isn't bolted to the body (at least, on the W123 with stock springs).

Once my differential/driveshaft/shocks were out, I could then remove the subframe mount bolts/plates and lower the subframe as a unit, if that's what I wanted to do. Given my tight and cluttered garage space, I opted to work one side at a time. Also, I wasn't initially going to replace the mounts. I only wanted to replace the trailing arm bushings, one of which was 100% obviously completely shot.

But, once I got this far, I realized that I couldn't reasonably access the outboard trailing arm bolts without lowering the subframe. So, I lowered the subframe one side at a a time and worked one side of the car at a time. That's when I discovered my subframe mounts were shot and decided to replace them, too.


But, all the while, my jack stands were under my jack points.

I pulled everything out at once.
First (and,hopefully last) time I've done this, so I can't compare
it to doing one side at a time. Also, the 123 & 126 subframe mounts
are different. Seemed easier to do the disassembly away from the car.

Swapped in alum trailing arms from a 500SEL with the anti-squat bar.
2.88 diff from a 85 300. Changed all the rubber. Also, I Por 15'd the subframe.
I am very happy with the results. Car handles nicely.

Next year.........the front end

Jeff

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