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  #1  
Old 07-13-2010, 10:33 PM
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W126 cracked trailing arm. Can it be safely welded?

The right rear trailing arm on my 89 300SE is rusted out on the bottom and cracked up along the rear edge. I can't believe I never saw it before, I must be going blind. The car has always had too much camber in the rear wheels, more on the right than the left. I've been under it a half dozen times looking at the shocks, springs and bushings but I guess I wasn't in the right position to see the crack. The rust out wasn't too visible until the arm was wiped off.

It was my indie that found it. I gave up trying the figure it out and took it to him. He thinks a good welder can repair it so that it will be safe, and that new springs and shocks will correct the rear camber.

Does this sound right to our experts? I'd love to get some opinions. Thanks.

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Old 07-13-2010, 10:42 PM
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I'd say that if it's rusted enough that it split at that point, the rest of it is very likely too far gone to even attempt welding, much less in a stressed application like the suspension of your car.

Don't get me wrong, I have nothing against welding as a tool for metal repair, but with the sheet metal that these cars are made of, I'm very cautious around the suspension.
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Old 07-14-2010, 03:16 AM
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Virtually every one here on this forum says not to weld these parts. I think for the cost of a good second hand one it is not worth the risk... it is a pretty critical part of the car.

The main problem with these parts is that they are hollow - the only way to spray them inside with anti rust stuff is to undo the lug that supports the parking brake (at the bottom) where one of these holes is drilled through into the cavity. The rust you can see on the outside is quite likely to be just as bad on the inside anyway...

Furthermore even if you could get it welded the chances of making it true are slim - you'd need an accurate jig to make sure that the rear suspension alignment was correctly set. Take a look at the FSM for accident damaged sub frame and trailing arms... Mercedes say you need to have the whole sub frame and trailing arms set up on a special surface plate - I bet you couldn't find a dealer who has that kind of kit!
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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

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  #4  
Old 07-14-2010, 08:07 AM
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Makes sense.

I'm sure your advise on replacing with a good second hand one is the way to go. Does anyone have one at a good price?
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  #5  
Old 07-14-2010, 11:15 AM
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B, you might try some of the recyclers on eBay. They may not have a trailing arm on their listing, since it's not a high-demand part, but give them a call.
I have had good luck with Ideal Auto in Chicago 773-509-9999 (Alex).
also SoCal dismantles a lot of 126's.

I found new rear subframe bushings to have more effect on rear ride ht that any other thing.
Also, the 300SE has a 9.5mm rubber shim above the spring. This can be replaced with the next thicker spacer (14mm, or even 19mm) to raise the ride ht. I did the subframe bushings and the 14mm spacer and she came up a couple inches, just right.

DG
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  #6  
Old 07-14-2010, 11:38 AM
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Trailing arm for 126

I have a trailing arm taken from a 1991 300SE which is my car. The car needed a wheel bearing in that arm and it was cheaper to replace the whole arm than to find someone who would do the wheel bearing. I have that trailing arm for the right rear if you would want to replace the wheel bearing.
I would sell the whole arm for $20 plus shipping. Let me know. In the meantime you can check out the replacement bearing cost. BTW, the car only has 97,000 miles on it.
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  #7  
Old 07-14-2010, 12:54 PM
LarryBible
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I would have to see it before I would make that call. It would require two things to be repairable:

It would have to still be such that it is dimensionally sound, and it would have to have some solid areas in the right locations to weld reinforcement to. You would never want to try welding it up without welding reinforcement material in a key location.

Actually a third criteria would be the material thickness that one would be starting with. I've welded up plenty of things over the years, but not too much patching on automotive suspension members. Under certain circumstances it can be done.

Welding is like painting, a big portion of the job is in the preparation.
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  #8  
Old 07-14-2010, 02:43 PM
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Forgot to say

Quote:
Originally Posted by Army View Post
Virtually every one here on this forum says not to weld these parts. I think for the cost of a good second hand one it is not worth the risk... it is a pretty critical part of the car.

The main problem with these parts is that they are hollow - the only way to spray them inside with anti rust stuff is to undo the lug that supports the parking brake (at the bottom) where one of these holes is drilled through into the cavity. The rust you can see on the outside is quite likely to be just as bad on the inside anyway...

Furthermore even if you could get it welded the chances of making it true are slim - you'd need an accurate jig to make sure that the rear suspension alignment was correctly set. Take a look at the FSM for accident damaged sub frame and trailing arms... Mercedes say you need to have the whole sub frame and trailing arms set up on a special surface plate - I bet you couldn't find a dealer who has that kind of kit!
Sorry I forgot:- there is another way to spray anti-rust stuff into a hollow trailing arm but you need to remove the hub and the dust shield. Just behind the dust shield there is a rubber bung in a hole too...
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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!
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  #9  
Old 07-14-2010, 02:47 PM
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If you decide to go down the route of changing the trailing arm instead of welding and you need to change the wheel bearings have a look at this thread

W123 rear wheel bearing removal help needed

(Sorry I'm a self publicist)

And piece it together with the DIY

http://www.peachparts.com/Wikka/W123RearWheelBearings

The thread shows an easier way of getting the hub in and out. You can even do the job off of the car.
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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!
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  #10  
Old 07-14-2010, 03:52 PM
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Question

Quote:
Originally Posted by bolomiester View Post
I'm sure your advise on replacing with a good second hand one is the way to go. Does anyone have one at a good price?
What state are you in?

I have some W126 trailing arms.
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  #11  
Old 07-15-2010, 11:53 AM
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Quote:
Originally Posted by whunter View Post
What state are you in?

I have some W126 trailing arms.

I'm in northern Illinois, about 100 miles west of Chicago.
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  #12  
Old 07-16-2010, 02:27 AM
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Answer

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Originally Posted by bolomiester View Post
I'm in northern Illinois, about 100 miles west of Chicago.
I will check my collection for the correct one today.


1989 300SE
Right rear trailing arm
MB# 126 350 33 05
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  #13  
Old 07-16-2010, 07:01 AM
LarryBible
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There you go! A good used one would be less trouble, probably less expen$e and take away any concern you might have about your welding skill.
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  #14  
Old 07-16-2010, 07:26 AM
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Quote:
Originally Posted by LarryBible View Post
There you go! A good used one would be less trouble, probably less expen$e and take away any concern you might have about your welding skill.
I'm totally convinced that a good used one is the only way to go. Several forum members have contacted me saying they have one. I'm just trying to sort out who has the correct part at a good price.

So far I can't understand if all w126s use the same one or if they are different. Hopefully it will all come together in the next day or so. I'm anxious to get it fixed. While I'm at it I plan to install new shocks and thicker spring spacers to hopefully correct the camber.
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  #15  
Old 07-16-2010, 01:46 PM
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Quote:
Originally Posted by bolomiester View Post
I'm totally convinced that a good used one is the only way to go. Several forum members have contacted me saying they have one. I'm just trying to sort out who has the correct part at a good price.

So far I can't understand if all w126s use the same one or if they are different. Hopefully it will all come together in the next day or so. I'm anxious to get it fixed. While I'm at it I plan to install new shocks and thicker spring spacers to hopefully correct the camber.
From what I have read here there are two types of trailing arms - steel and aluminium. Both fit on the w126 and w123 models.

Are you aware about the differential mount that can also cause sagging - I assume that is causing an incorrect camber on your rear wheels?

It is worth your while checking the length of your uncompressed springs before re-assembling your suspension and the thickness of your existing rubber spring mounts... I've just put my w123 suspension back together (front and back) putting back in 3 nub rubber mounts after replacing all of the other rubber components. Checking with the data in the FSM the "new" suspension was within limits.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!
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