[T3] Generator ... Again

[Jim Adney]

I've been scratching my head over the early 12 V generator Max sent 
me, trying to figure out what's different about it, that would have 
made a different brush necessary. I had always assumed that there was 
something different about the diameter of the commutator, the 
geometry of the brush guides, or the position of the brush spring 
anchors, so here's what I've done:

I have a 1970 publication from Bosch, detailing all the parts in all 
their generators. It calls out the same brush springs and the same 
armature for both, yet it calls out different brushes. It also calls 
out different end plate assemblies, but they are different in ways 
other than the brush holder dimensions.

I've taken apart a late 12 V generator so I could measure and compare 
the dimensions of the brush guides and spring anchors. I can't find 
any difference that would appear significant.

Yesterday I biked down to a campus shop that I thought might have one 
of the obsolete brush sets. They pointed me to a box marked "Obsolete 
Bosch brushes," but there were no Type 3 early 12 V brushes. I have 
one other place I'll call later this morning, but I'm not too 
hopeful.

The brush set I'm looking for is Bosch # 11 020 (long #2 107 014 
016.) If anyone can find one of those sets, I'd love to buy it from 
you so that I can KNOW what the difference is between it and the one 
that superceeded it (11 004.)

Okay, more confusion. From thinking about this for years, my 
conclusion has always been that one critical feature is that the ramp 
on the top of the brush ramp down toward the pigtail. Now i've 
actually looked at some of my bagged Bosch parts and see that the 
ramp goes the "wrong" way on the 11 004. It goes the "right" way on 
the 11 008, which is the Bosch replacement for beetles. To my 
thinking, the ramps should be different because the direction of 
rotation, with respect to the brushes, is different, from Type 1s to 
Type 3s.

This boils down to me and Bosch coming up with different 
recommendations. I have GREAT faith in Bosch, so I've been trying to 
understand why the other ramp direction would be better, but at this 
point I can't. I really hate to stand here and say that I'm right and 
Bosch is wrong, but that's what it seems to be boiling down to.

Add to this the fact that I looked at the ramp on the brushes in my 
'71, which are probably the originals, and probably close to being 
worn out at 80 kmiles, and they slope down toward the pigtail, like I 
think they should.

Now comes the real puzzler: My 1990 info shows the original part 
being superceeded from 11 020 to 11 004, but I just got a call saying 
that the 11 020 is superceeded by the 11 008 (which has the ramp the 
way I think it should be.) At this point, I'm thinking that Bosch is 
wrong and is discontinuing what they think of as the Type 3 brush, 
but this turns out to be right for us, but wrong for beetles.

I think I need to find some more modern Bosch info, to see what it 
says, but at this point, I think I've done just about everything I 
can.

What I've done on Max's generator is to file down the ramp a bit, so 
the spring doesn't have to reach up so far, and bend the spring a bit 
to give it a bit more reach. The problem that I think occurs is that 
the spring tends to push more sideways than down, so that the brushes 
eventually hang up and don't make good contact with the commutator. 
When that happens, the surface of the commutator gets burned and 
rough, wearing brushes out quickly until the commutator is turned 
smooth again.

If anyone has another theory, I'd love to hear it.

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