OMG my head is swimming. I took a peek under the rear to see what might be causing the recent sag and was greeted with this.
There has been rust on the bottom part for a long time that had received some light patching with a welder to limp it along, but now it’s over Johnny.
It is cracked at least half way around and looks like it could snap with the next big bump. A search around the forums emphasizes the opinion of a machinist in-law who says suspension parts should never be attempted to be welded so repairing the crack by welding seems out of the question.
A scout around the area confirms that this looks like a huge undertaking. There is soo much attached: wheel, joint, springs, strut, brake lines, pressed bushings.
How much time are we looking at here to remove and replace with another one?
I don’t see any donor cars on my local craigslist and local junkyards are some genuinely terrible and overpriced people to deal with.
I’ve been calling this a “swing arm” but it seems that the correct name is “trailing arm”. Is “trailing arm” the correct name that I need to be asking for?
Somebody tell me its going to be alright and I can knock this project out in an afternoon or two 
Anyone in driving distance of Chatt. TN that has a part I would be glad to hear from you too.

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

Wow! Yea... I would not be driving that any more.

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AJ

1985 300D (SOLD)

Hey of course it is going to be alright.

I'm half way doing my front and rear suspension... my car now has only one wheel - the steering wheel!

I've also dropped the subframe and dragged everything off so if you need some pictures PM me.

Access to the mounting bolts on the trailing arm is tight on a W123 but some say that you can reach them with out dropping the subframe. (search this forum) Give it a go - you need a 24mm spanner and a strong arm.

I think you'd be better off removing the axle so that you don't damage it - though I bet it has been done with it in place. If you remove the axle you need to drain the diff and remove a fiddly circlip.

For safety's sake I would remove the spring with a Mercedes spring compressor which means you need to take out the rear shock - the back springs are shorter than the front but they are seriously powerful. (Search this forum on spring compressors to see warnings regarding cheaper options!)

You also need to disconnect the rear stabaliser bar - but this is very easy.

If you buy a second hand trailing arm make sure you get one with a good rear bearing - replacing this is complicated as you need a special tool (Sorry but search this forum again for that one too!).

With the right bits and a good work space I think I could (now) easily do it in a day - with a nice Italian style lunch in the sun!

Oh yes sorry I forgot about the brake caliper and the brakes as well...

Clearly this is from WVO use.... !

If you haven't already, put a post up in the 'Parts' section. Somebody can help you out Im sure.

It is possible to get this done without the spring compressor.
http://www.peachparts.com/Wikka/W126RearShocksSprings

If you have changed an axle before, you can do this in an afternoon or two.

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

You have PM.

I'd replace it as a whole unit with a good used one. Easy if you do it that way.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

WOW, that is scarry looking . better hang up the keys and not move it.

Start looking through the PNP for a low milage 123 or 126 and pull the trailing arms. they are about $42 ea with the hub.

I just replaced sub frame bushing and trailing arm bushings. not that big a deal to drop the whole rear end assembly. (now that I have done it)

You cannot remove the trailing arm w/o droping at least one side of the sub frame. there are 2 24mm bolts that are inacessable to get to. and dang, they are tight.

If you are just going to R&R the one trailing arm w/o doing bushings etc... all depends how good of a DIY you are and mechanical skills. a good week end job.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Here is a good thread on removing the sub frame etc....

W123 1984 300TD wagon rear trailing arm bushings R&R

with 3 floor jacks, the whole assembly can be lowered down and rolled out the back.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

if the trailing arm was that rusted, you may have some issues with hardware removal to drop the suspension.

I would crawl under there and see just how corroded all the nuts and bolts are, and I would get access to an oxy-acetylene torch just for good measure.

Something that would take a day and a half with good hardware, may take you a week if you can't move the nuts and bolts.

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This post brought to you by Carl's Jr.

Stress Corrosion Cracking ~ a combination of salt, rust & vibration.

What does the other side look like?

Who ever welded a patch on it should be stoned in the village square!! Its just stupidity to do that sort of repair on that!!!

Lucy its still sort of in one piece. Could have easily caused the car to roll over.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Come purchase an entire w126 parts car from me. Bring a trailer and I will personally load it for you. See my w126 gasser parts cars thread in the Parts Forum.

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daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
No longer selling Cluster Needles Paint
No longer selling New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more

day_two If I pull up to the house towing a parts car it would just be to pick up a bag of clothes and the divorce papers. If I were to try to buy a parts car I would have to have it gone again fast . If I stripped out a donor car at my house I don't know how I would get the carcass back on a trailer to get it out of here. Do you have an arm you can sell me? The problem is going to be what dropnosky says...
OK. I said I was looking for words of encouragement, NOT the truth.
Two years ago I replaced the rear springs and spacers. Had a big mission with the bolts that went into this arm but the problem was more an issue of coming behind someone elses work with stripped threads and missing bolts and such.
Clearly because the driver window not rolling down as well.

I wish we had something like Pick and Pull around here. We don't have anything that even aspires to be like it. Anyone have any leads in Atlanta? Memphis is like 6hrs away

I think I saw a thread somewhere that said what other model arms were interchangeable. Anyone have that bookmarked?

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

This the chart?

Replacement Trailing Arm

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

According to this chart, the W126 trailing arms for the 126.039 are interchangable with the W123 trailing arms.



The curious part is that the 126.039 is a 560SEL, which does not have the same trailing arm as any W123 or W114/115 I've ever owned....

The 560SEL, and I suspect, the 560SEC have a forged or cast light metal (magnesium?) arm, which if this chart is correct, would be a direct sub for the rust prone stamped steel type.

It would seem worthwhile to seek out a set of these arms, if indeed they interchange directly....

Euro 500s also have 560SEL style trailing arms.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles