Whenever possible, remove the component from the car before welding on it.

As I meet those involved in DIY car maintenance, I am often asked (and sometimes given) advice on technical matters. Recently, a young mechanic and I were talking about carrying out welding jobs on modern vehicles.

The truth is that arc, MIG, or TIG welding on a vehicle puts all its electronic devices at risk. And when you consider the cost of replacing airbag and engine management systems, radio/tape and CDs and associated sensors, plus alarms and alternator, welding without the necessary precautions could prove an expensive exercise.

However, many garages do not take any precautions and most of the time they get away with it.

But is it a gamble that is worth the risk?

It helps to know exactly why and where the danger lies and to ignore certain “precautionary measures” that are of no use whatsoever. For example, some claim that disconnecting the battery while welding is a safeguard against damage. Others say that setting the earth clamp close to the weld is the way to go. The fact is that both make no difference at all.

The current and voltage of the welder itself should present no problems; rather it is the inevitable voltage spike that occurs each time the arc is broken or switched off. While welding a strong electromagnetic field forms and this collapses when the arc is cut/broken off in turn producing a voltage pulse that may damage the electrical circuits.

Where it is possible, the best bet is to remove whatever is to be welded from the vehicle and weld it before refitting. If this is not possible, remove any electronic components in the immediate area of the weld and disconnect any others.

It’s probably safest to contact a main agent either to get the job done, or to ask advice on where to get the job done. Enough said.


Because noises tend to develop slowly rather than in one glorious bang, they often go unnoticed and even when impossible to ignore may be easily misdiagnosed.

The case I am thinking of involved an old Renault. The owner suspected a worn wheel bearing, but after checking all the wheels for noise, rough running and play he took the car to a main agent and was told that the diff bearings in the gearbox were to blame and that repair parts and labour would cost more than the car was worth.

Although it is recommended that the engine and gearbox are lifted out together, we lifted out just the gearbox and decided that a good gearbox from a breaker would be a more economic way to do the job. After phoning several breakers, we finally located one with a suitable vehicle from which a suitable gearbox was available. The donor vehicle had been front-ended and written off. The gearbox in fact cost far less that those needed to put the original gearbox right.

With the replacement box fitted, a road test was carried out and the old Renault was quiet again. - Star Motoring