w124 easy weld or nightmare?

[millo777]

Having stripped out the interior of my w124 to dry it out and trace any further leaks I found a small split in the weld between the rear arch and the main body, under the rear seat. As per photo.

No idea if this a source of the leak or a symptom of it, but it needs fixing.

The strange thing is that the split appears to be into a box section and there is no sign of any problem on the underside or from the exterior of the wheel arch.

On that basis, is it any easy weld done from the inside of the car, or do I need to dismantle half the car to check whats happening on the other side of the problem? is there at least reasonable access to put some cavity wax on the reverse side after it's been welded?

 

[grober]

Its highly unlikely that this is the source of your leak-- but it could be. These cars are usually spot welded together rather than seam welded. My guess is that its just the sealant on that seam that has gone. Cleaning up the area and application of a suitable mastic sealant should cure any leak. On the other hand the leak may be coming originally from the rear side windows[ known weak spot] and flowing down inside the trim to floor level. Have you checked the other side for comparison. It's possible that a spot weld or seam weld has gone I suppose. Welds can act as a focus for corrosion due to the galvanic effects of the different metals involved but if the rear end of the car is not falling off I doubt if there's anything structural to worry about. Some of the forum members who are into welding the W124 model may be able to comment more fully?

 

[jaymanek]

Doesnt look split? Just looks like dirty rusty stuff, maybe caused by seat base touching there.

I bet if you clean it back there isnt a split?

 

[RBYCC]

+1^

 

[millo777]

There is definitely a hole there that I get the end of a flat blade screw driver through. I thought it was probably caused by the leaky rear window, which is now properly sealed.

So the consensus is that it wouldn't need welding, providing it's cleaned up and sealed properly?

 

[jaymanek]

Its one of those places that I wouldnt bother, in the long term you will probably do more harm than good.

I would, clean the area back, use some rust treatment, then primer then a good sealant...

 

[millo777]

I was kind of afraid of exactly that, doing more damage in a fix attempt. For now I'll take your advice and clean iit up and seal it. Hopefully i can get some wax into the box section to treat the other side.

Thanks for the posts. The joys of running older cars are never ending.....

 

[jaymanek]

Im not sure exactly but I guess that will be accessible from the transmission tunnel.

 

[RBYCC]

Scrape the sealer from the area until you get to unrusted clean metal.
Sand the area down with a 120 grit sandpaper to bare metal.
Cover with a zinc enriched primer.
Get a good quality spray can of undercoating and use an nozzle extension tube to spray through the hole and into the cavity.
You can coat the repair but the primer should suffice.