[T3] muffler - HE leaks

[Jim Adney]

Exhaust leaks between the ends of the lower heat exchangers and the 
muffler are generally caused by rusting on the OD of the HE tube, leaving it 
smaller than when new. The reduced OD makes it hard/impossible for the 
crush rings to seal to the tube. This problem is made worse by most 
aftermarket exhaust systems, which use inch size tubing which has, by 
necessity, larger ID than the metric size it replaces.

In extreme cases, the rust can even penetrate the full thickness of the tube, 
eventually causing the end of the tube to break off. I have aftermarket repair 
ends made to fix this. They have a tapered fitting on one end that is a tight fit 
in the ID of the HE tube while the rest of the fitting has an OD which matches 
the new OD of the HE. These repair tips are installed by cutting the end of 
the HE off and tapping the repacement into place. They go in tight and some 
mechanics tell me that's all you need to do. I prefer to weld them, which can 
be done in place.

If you have the time and inclination, a better option is to weld up the low 
areas on the HE tube and then grind them down to the correct OD. This 
makes a really good repair, but it is also quite a bit of work. I've only done 
this job once, since it requires the HE to be completely removed from the 
engine.

Short of one of those repairs, I recommend alum flashing strips and muffler 
cement to fill the gaps. I've found the muffler cement to be much more 
durable than I expected. The key is to get some of the alum "shim" past the 
sealing area under the crush ring and into the space between the OD of the 
HE tube and the ID of the muffler inlet pipe. In other words, on aftermarket 
systems, you should get part of your shim pack in past the flare on the 
muffler tube. This will prevent vibration between the muffler and HE tube, 
which would cause the cement to crumble and leak.

I suspect that exhaust gasses blowing forward from a leak there, and into the 
heated fresh air chamber of the HE, is the biggest problem that these leaks 
cause. This is often misdiagnosed as due to a leaky rear door seal, but I 
think that problem is rare. The fix that Phil mentioned puts a deflector on the 
HE tube, to divert the leaking exhaust gasses away from the fresh air 
chamber. It's easy and effective.

I find that these problems are much less common with stock mufflers. That's 
the reason I went back to stock after many years of dealing with aftermarket 
systems. If you're interested (shameless commercial) I have all the stock 
system parts available here. I also have good clean, nearly rust free heat 
exchangers, both lower and upper. Those parts are all more expensive than 
the aftermarket replacement, but they fit better, last longer, and give more 
peace of mind.

Finally, I should mention that John J's Sophy had an aftermarket system at 
the last invasion that I had not known about. It was a stainless steel adaptor 
from his J-tubes to a stock Type 4 muffler. That seemed to fit and work really 
well. The only downside I could see is that Type 4 mufflers are even more 
rare and expensive than Type 3 mufflers.

John, who sells those?

My apologies for the long post.

-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************