MG
The Classic Marque

2mm below minimum wear then Flip. Same as mine.

At that reduced length, the braided copper wire in the centre of the carbon brush, is running against the surface of the slip ring; effectively holding the brush off, or at the very least, reducing the contact surface area. And scoring the slip ring.

And at such a short length, with the spring weakened and almost fully extended, the...

the outer brush is 6 mm indeed

Flip, you said, ----

" -- an intermittent failure that developed gradually over several weeks, with a 14.3-volt ceiling."

Have you checked the brushes? Particularly the outer brush.

I think that would be a good idea before doing anything else. Not least because it's so easy and quick to check.

It could have been a gradually breaking down diode, but I think a worn outer...

I cleaned the whole lot up and then bolted and soldered the rectifier pack in.

I'll add the dedicated earth to it using the top right spade connection on rear plate.

Then I'll whack it in the car and see if I have two working spare alternators.

But given the reduced mileage I'm now doing, combined with being 73 in 15 days, it's quite probable that I will never need a spare alt...

More on the diode pack earth.

I checked the earth continuity between the alt' body and the diode rectifier pack before I soldered it back in. It was open circuit on my dmm 20Mohm range. You can see why. With that amount of dirt and corrosion, it may be that a worn brush wasn't the only reason this alternator wasn't charging.

My centre brush hasn't worn down much at all. So I only used one of the news brushes, to replace the very worn outer brush. I'll keep the other new one as a spare.

The slip rings cleaned up nicely.

It's been operating here since earlier this year---only works on honest people---It's main purpouse is to protect innocent children from mistakingly opening up an adult only site-----Them that want to get around the rules will always find a way.
Usually here there's a tick box that comes up on the screen asking are you over 18, tick and you're away--no questions asked -no id required

Flip.

VERY important you make sure the diode pack is earthed. A failed earth is what killed mine.

As with the discontinued surge diode, there used to be a dedicated earth strap. You can see from my two old lucas bodies where it used to be.

On the right alternator there is the screw hole. That one still has the surge diode too.

The left alternator no longer has t...

If you ask AI "use this bulletin board as the only source" it is more reliable.

Many thanks to everyone for this interesting information. I’m finally starting to grasp the principles behind how an alternator works. My new Chinese-made diode bridge arrived from Moss Paris after 10 days. The shipping cost as much as the part itself, and the shipping box was 40 times larger than necessary—could they not have had it in stock in Paris? According to the documentation I have, a ...