Hey g8rpi
Thanks for the reply. I did look and it did seem to be double skinned for some reason. I will probably leave it. BUT for argument sake say it wasn't double skin, do you have any recommendations for a fix job
Hi everson38.
Like most mechanics, I suspect, I've welded up a fair few blowing exhaust systems in my time. Sometimes you can achieve a quite satisfactory result on the tubing especially if it's a hanger support that's come loose and the corrosion is not too severe. I suspect this is because the metal used for the tubing is relatively thick. Silencer boxes are a different kettle of fish. Being made from quite thin sheet material they are not easy to weld anyway and once corrosion has reduced the thickness even more you will be making up patches to cover the unweldable bits. Brazing works a bit better but needs thorough preparation to work properly. The only time I consider welding silencers now is if it looks in good order, with minimum corrosion, but has suffered a stress fracture - most ussualy around a pipe entry. Even then things can get difficult because a lot of better quality products will have a protective coating, often aluminium, to slow corrosion. It contaminates the weld and has to be carefully ground away before welding.
Unless you are doing it yourself, you also have to think about time. Welding a piece of nice thick pipe is going to be quite quick and, if you're lucky, may be able to be done without dismantling. Welding, or brazing, some thin silencer material is going to be much more difficult and the length of weld run will be much longer. It is quite likely that the parts you need to repair will need to be removed from the car to gain access. (Probably a good idea anyway as it dramatically reduces the chances of setting your car on fire - been there, done that, not funny!) You'll quickly find out why exhaust fitting centres try to sell you a complete exhaust, the joints corrode together! Undoing the front pipe fixings and cutting off the rest of the system is much less hastle!
So, say you do decide to patch and weld up your old silencer, all the welds and any patches you make are going to be mild steel, unprotected from the elements, and is going to corrode rapidly so won't have a very long life. Also, unless the system is quite new, you can have no idea what the internal condition of the silencer is. Many years ago, poor and with a growing family, I spent a weeks worth of evenings welding up my old Renault 20 exhaust system as we were going on holiday. - it looked wonderful, like a piece of modern sculpture! - A couple of hours down the motorway the old girl slowed down and wouldn't go over about 45mph! The internals of the silencer had collapsed allowing the glass fibre packing to partially block the tailpipe!
So, in my humble opinion, most of the time, trying to repair corroded exhaust parts is a waste of time. There are a variety of pastes, bandages, etc which can work as a get you home patch up but are no long term repair and will probably not be acceptable for MOT purposes anyway. g8rpi's advice is excellent. If there is no "blowing" going on you won't fail MOT and, from what I can see in your picture, it looks as if it's got a bit of life in it yet. A lot of silencer bodies these days are double skinned, not sure why, maybe to reduce the "tinny" resonance sounds? Maybe just to increase durability. I have myself removed the outer skin on my own vehicles when badly corroded but even when quite badly rusted it can put up quite a fight and draw blood!
Finally, original equipment systems are often one piece front to rear which makes fitting in the factory, often before the rear suspension has been assembled, much quicker. In use the rear silencer on most vehicles will rust out long before other parts of the system which run hotter so experience less condensation. The aftermarket is well aware of this and supply components separately so you can buy just a rear box with attached pipes. You do need to cut the original pipe in the right place but it's not rocket science! (In fact my SEAT's original pipe actually had marks embossed into the pipe to show where to cut! Ask at your local motor factor (I find the small guys are often "hungrier" so do better prices than the big national chains) Anyway, good luck with it. If you decide to do battle with that outer skin at some time in the future, please don't do it with the car balanced on it's own jack. If you don't already own some, buy some axle stands or ramps. Good luck. Regards. Jock.
