02 December 2010

[VW] Sam and the Art of VW Maintenance: Ye Olde Generator Brushes

I, for one did not know that generator (Type 1's before 1973 or 74 or 75 or summat, didn't have alternators, they had generators) brushes wore out.

Perhaps that's because in the past, whenever any car I had had an alternator problem, it was just replace the alternator time. This is one of the simpler fixes - depending on car, of course - that the unskilled DIY mechanic can accomplish. On the 70s VW Dasher, the alternator was held to the engine block by a pin hinge and was spaced off by an arm down which a nut-n-bolt slid. swivel out the alternator far enough to get proper tension on the belt, tighten down ...   you're g-squared.

What the brushes do is quite important. The part that spins round in your gen/alt, the rotor, creates electric power because it's a collection of loops of wire whirling around in a stationary set of magnets (the stator). Because of The Way Things Work Around Here™, when you physically pass a wire past a magnet, the wire's cutting the lines of magnetic force cause a current to flow. Get enough of them whirring past a magnet fast enough and you have enough current to power a car, charge the battery, and run your trusty AM radio or what have you.

If you've got all this electric potential going on in the rotor you've got to get it out of there somehow. Therefore, from another point on the stator you run a short rattail of thick copper wire to a piece of metal that rides a set of contacts on the axle of the rotor, where you tap that current off. And that's where your brush is.

Now, it stands to reason that enough years of friction there will cause it to rub away (though this won't necessarily occur to you if you haven't ever taken a generator apart, even if you do know a thing or two about electricity and how it's produced). What you do know, however, is that after all that expen$ive work getting a new engine into the car, all of a sudden, you have a generator light that won't go out.

Glad we got us that new Schwab battery back when the old engine blew. It got me started and around town for a few days. And the generator light, to be fair didn't suddenly go out: it would pop on at idles, the go out when I revved, until one evening when it wouldn't go out any more no matter how much revving I was doing.

Back to Mechanic Bill's house. He nailed it pretty quick. Generator brushes shot, no more left to them. It was a $70 repair, but what Bill's crew fixes tends to stay fixed, and the generator light hasn't given me a problem since.

Now, we will have the horn (which won't) and the four-way flashers (which don't), and Bill pointed out to me and The Wife™ what parts to go looking for. Like a true old-school VW mechanic, he'll do the work and bill you fairly, but if you're out of bread and might be able to fix it yourself, he'll point the way.

Oh! Which reminds me! I mentioned to him that I was a fan of Muir's famous Idiot's Guide and he said he had an old copy he could let me keep, and he did, and I do. The meat and potatoes of the book are unchanged enough that the copy I now have - a 1982 edition - will serve me in good stead until I get a more modern printing (which has nifty background information). But that's a pretty sweet thing to do for a customer, give them such a valuable book and advice on top of the repair, which made it really worth the $70 - turning it from money from a tight budget spent into money invested in having a 72 VW Beetle that'll keep running and be dependable for a good long time (it is to be hoped!).

Here (http://www.reluctantmechanic.com/step-by-step/change_generator_brushes.php) is a very good description of what the tyro should go through in replacing the generator brushes, with apropos photos. Be enlightened!

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