Frame rail rust!! Help!
 

I have an 81 300TD turbo
I was checking out the rear underside(for self leveller rebuilding) when I noticed some rust in the rear frame rails, mostly where they meet the cross member the differential mounts on (right next to the rear wheels)
This is the same area the brake lines attach as well as the bars from the self leveller.
In these two areas the frame rails seem pretty well rusted.poke your screwdriver through rusted..not good
IS this a ditch the car problem or does the unibody hold together despite this
It gives me pause for the possibility of towing too

HEEEELLLLLPPP!

I hate to tell you this, but I think it is terminal. Save it for parts and get another one.

Thanks
I appreciate the truth in this instance regardless of whether it's good or bad news

Just to clarify it's not the entire rail(s), mostly just at the juncture of the horizontal member and the two rear rails that are on either side of the gastank
To me it seemed like a bad thing
Any other opinions?

Can you post pictures?

yeah, pics are critical.

If I understand you correctly, you have some serious rust that is NOT easy to repair, and it's quite important for rigidity of the vehicle.

you are describing the rails between the bars that are parallel with the rear bumper, yes? and the rust is on the section that the rear subframe is bolted to?

start looking for a replacement car. this level of rust repair is NOT for the even experienced body man...

Yeah put up some pics here or on BW then we can give you a better idea.

Pictures
 

Ok here's some under the car with the @%#@^ camera pictures
The first 2 are the passenger side
the next 2 are the drivers side
both sides are poke through rotted in places, the drivers side is worse

If you really wanted to you could fix it. I'd think. It would be work but I think its possible. You'd have to remove the torsion bar and all the stuff in the way, grind it down to bare metal. Then I'd get some 1/4 steel and weld/bolt it in for replacement. Lots of work but do-able IMO.

I'm sorry to say but if you gind that there won't be much left.

I'm not saying don't do it but don't get too depressed if you only have flakes on the ground by the time you've finished.

Even my car doesn't have rust like that up there =>

http://www.peachparts.com/shopforum/body-repair-restoration/303669-my-w123-saloon-sedan-old-accident-repair-bit-rust-repair-thread.html

ok, at least that's not structural...
this car is not going to be restored to concurs condition, but you could clean it up, and treat it.
I'd not remove the torsion bar, keeping in mind, the bolts will likely either snap off, or twist out the nuts from the frame... I'd just wire brush out the nasty stuff, paint it with por-15 a few coats, then pop rivet some metal over it, with JB weld sealing the seams, and underbody coat over the repair.
that'll keep it from getting worse.
I'd also start shopping for a better replacement.

Why do you say not structural John?

I'd say very structural for a monocoque - look at that flaky stuff right next to the roll bar mounting bolts. When it gets flaky it comes off in big lumps...

...you shouldn't be wire brushing this with a hand held wire brush - go at it with an angle grinder and a wire brush attachment. It is all very well hiding stuff under POR15 but the paint isn't strong enough to hold it all together.

it looks like it's on the H beam, not the rails, it should not be integral to the ridgidty of the car. Sure, it'd affect how the vehicle handles a wreck, but should not fall apart driving.

The area I photographed (the junction of the rails(?) and the cross member is te primary rear and rusty bit
The rest of the rails extending sft are good (I was banging them to test them). the spare wheel well is rusty and there's some corresponding rust on the other side.

Even it does fall apart there while driving, you will still have your front wheels for steering. ;)