Got this problem with my '65 Baja bug. After years of off-roading in the desert and mountains of Arizona my left rear IRS wheel tilts in at the
top. After close inspection I find cracks almost fully around the rear torsion tube where it meets the rear horn. These cracks have allowed the left
rear suspension assembly and wheel to sag. And its getting worse. Also, there's this little bit of support between the spring plate housing and
the chassis that was broken (I believe it was cast iron?) that was maybe allowing movement in the torsion tube. As I see it, any movement inthe
torsion tube would allow the metal to crack.
So, what's going on here? Why is my torsion tube cracking, and has anybody had the same thing happen to them and whats the best way to fix? I
will tell you this past weekend I tore down rear suspension, re-aligned everything, then re-welded everything. But, after a 1-day safari in the
desert the thing broke again. Now what? What forces are acting on this thing that I don't know about?
From Phoenix, Arizona...Helppppp.
-John
Unfortunately, metal is prone to stress fractures and metal fatigue. Metal in this condition will not be fixed by welding, particularly cast parts.
The heat of welding tends to work harden the parts around the welds, which reduces the metal's mallability and causes it to fracture rather than
flexing.
I think it might be time for a new rear end for you. It might be a good idea to brace it before it breaks, as an added precaution. Take a look at some
offroad racers to see what sort of tricks they use. 
Thanks, Kruizin, for answering. But I have this question..is a new or replacement an option? I'm not sure how the rear chassis of a T-1 is
built and if if can be repaired.
Have an idea?
-John
The problem is caused by the constant pounding that the suspension takes during your offroading forays. Vibration is a killer. That's why rattle
guns work on wheelnuts when a wheelbrace won't.
Have you got any photo's of the problems? It would sure make it easier for people to take a stab at it if they could see it.