Reinforcing Rusty Frame - PeachParts Mercedes-Benz Forum

Cigar Havana · #1 06-17-2012, 03:36 PM

Hi
I am interested in doing some welding on 1989 420SEL, specifically to reinforce rusty lower control arm body attachment points.

Could you specify the steel specifications that should be used? What type of weld do you recommend?

I have never welded before. Is this something a novice can do? The weld job does not have be pretty, but it does need to be structurally sound.

I have attached a photo of the problem area in another thread

1989 420SEL Lower Control Arm Rear Mount

andydiesel · #2 08-15-2012, 09:45 PM

The metal on the mount is fairly thin - about 3mm. It may be higher strength steel, since it's structural. Unless you have access to graded steel, it may be difficult to obtain.
Last time I checked, the complete mount was still available from MB, but at an unworkable price.

It is not a job for novice welder...but I have seen poor professional fixes (time=money). I cut the mount in two and separated it from the frame rail. The frame rail will likely need welding too, some of it overhead.
The mount base plate (where the nut is located) can be cleaned off and reused. New upper part of the mount can now be made up.

To remove the rusted nut, break off what remains of the wings.

If mount needs welding anyway, cut a larger access opening to suit standard wrench.

If mount is still good:
Find a piece of flat stock, about 3/16" thick, a little wider than the width of the access slot.
Now make a square slot the size of the nut near the end of the flat stock.
Soak the nut in penetrating oil and give it a try.
The "wrench" will need some tweaking to work.

Stretch · #3 08-16-2012, 04:03 AM

I've not seen that part of the body on a W126 before but I can say that on my W123 the steel there is no thicker than 1mm

I think most people would call that an uneconomical repair. That means that only a DIYer would probably want to repair it.

You might find that people like klokkerholm make a repair piece for it though. There's a similar bit available for the W123. It is a complicated part of the body to repair though as I think you can only weld from one side. Distortion could be a problem. As said before a really skilled welder is required.

Cigar Havana · #4 08-16-2012, 12:34 PM

Hi
I took the car to a shop. They removed and replaced the bushings, bolts and nuts. To do 4 big sub-frame bushings, lower control bushings at both ends, welding with undercoating, and new eccentric pins with new bushings, and a wheel alignment cost me 13.5 hours labour.

All 3 bushings on each eccentric pin, had to be pressed in, the fit is too tight to install them, while on the car.

Stretch · #5 08-16-2012, 05:29 PM

That's an impressively short time - two people working together?

andydiesel · #6 08-16-2012, 06:46 PM

Found some photos of my repair....unfortunately only have the finished view of the RHS, the first photos show LHS. On second photo you can see the support cut in half...
Where the two halfs join, there is an internal backing strip. All rust has been removed from inside of the support. Frame rail rust has been cut out and fresh metal welded in...I recognize this is not a commercially viable repair. I may have spent 13.5 hrs repairing just one side...

Cigar Havana · #7 08-16-2012, 09:21 PM

Quote:

Originally Posted by Army

That's an impressively short time - two people working together?

No, one mechanic. Told the guy just to cut off the old parts, don't try to save the bolts or nuts. I brought it in at 8 am on Monday morning and it was finished 3 pm on Tuesday. Mechanic also did 2 test drives to make sure all was ok.

Stretch · #8 08-17-2012, 02:33 AM

Thanks for posting the pictures.

Those are some brave cuts - can you ask him how he aligned the new metal to make sure it is at the correct position and height compared with the other side? (I'm about to try and do the same to my W123 so I'm looking for tips)

I must say 13.5 hours for one side is still pretty quick - I got the impression both sides had been done in that time!

Cigar Havana · #9 08-17-2012, 02:23 PM

First, it was 13.5 hours for the complete job, not just one side.

Next, those photos are from another member, not from car. I can post photos of my car if you want.

I don't think there was an alignment issue. There was enough existing metal to hold everything in place, especial the bottom plate. The bottom plate is about 1/4" thick where the rubber bushing meet the frame. Also, those rubber bushings have an aluminum core, so they are not all rubber.

Stretch · #10 08-17-2012, 02:35 PM

Quote:

Originally Posted by Cigar Havana

First, it was 13.5 hours for the complete job, not just one side.

Next, those photos are from another member, not from car. I can post photos of my car if you want.

I don't think there was an alignment issue. There was enough existing metal to hold everything in place, especial the bottom plate. The bottom plate is about 1/4" thick where the rubber bushing meet the frame. Also, those rubber bushings have an aluminum core, so they are not all rubber.

My appologies I see what's happened now.

I think 13.5 hours for the whole job is very quick. I'm glad to hear there wasn't an alignment issue. I think there will be for my W123 - it is made differently.