[T3] Generator ... Again

[Jim Adney]

On 3 Sep 2012 at 7:12, Max Welton wrote:

> This generator was a re-manufactured Bosch unit I put in last
> November. At the time, I also replaced the VR with one of the new
> solid-state units. Buss voltage has been very consistent up to
> yesterday. 

I agree that's much less lifetime than you should get. Frankly, I've 
never had one fail, but we have to consider that rebuilds are 
generally made from someone else's rejects. I've got several good 
used Type 3 generators. Until this year, I'd only ever sold one, and 
that was in exchange for a Bosch rebuild that wasn't working out. So 
far this year, I've sold 2.

That Bosch rebuild turned out to have a badly out of round 
commutator, which is guaranteed to eat brushes rapidly. I turned it 
properly and it's fine now. Put your finger on a brush when the 
engine is running. If you feel it trying to vibrate up and down, 
that's a problem

It's always possible for field windings or armatures to develop 
shorts or opens after a long life. Those failures are unpredictable, 
but they also tend to be few and far between.

I could rebuild one for you and exchange it for yours, if you like. 
That entails some extra shipping cost, but at least you can be 
assured that the work was done well.

A couple years ago we got rid of our Ford Taurus. That car had been 
pretty reliable for ~140 kmiles, but it had gone thru 3 alternators 
(US made) in that time (14 years.) It's original, new from Ford unit 
lasted just over 3 years. I also just replaced a dead Bosch 
alternator on a Mercedes. So don't get the idea that an alternator is 
likely to be any more reliable than a generator. My experience is the 
opposite, because generators don't have semiconductors inside them.  

Look at your brushes. If the tops are below the brush holders, then 
they may be worn out. In this time they should not be. Mine last 
decades. Look at the ramp in the top of the brush. It should slope 
down going away from the brush spring. They are often wrong (beetle 
brushes) but can be easlily fixed with a file.

If you can push down on the brushes and make your problem go away, 
you may just need to re-file that ramp.

Remove both wires from the generator. Put a voltmeter from D+ to 
ground. With the engine running, ground the DF terminal. The voltage 
should go way up, especially if you goose the throttle. If it 
doesn't, then the generator is at fault.  

Look at the top of the generator body. There is a line stamped there, 
above the part #. That line should line up with the dot on the 
generator strap. If it doesn't, the air cooling holes won't line up, 
and the generator can burn up. A lot of these generators die simply 
because they didn't get installed right.

Remember, the devil is in the details.

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