I was reading this thread last week and by Friday last week my alternator crapped out........('77 300D)

Finally got around to checking things today.
I had only installed a new voltage reg with new brushes 3 years ago and it had not done much mileage since, being parked up for 2 years.

Just to make sure, I check the connections at the alternator plug:
12.81V at both the output wires, 12.52 at the excitement lead. Obviously this voltage drop is expected with the bulb in the circuit.

So I yanked the alternator out, and pulled the reg brush unit out and found a brush had broken off. The remnants of the broken brush had worn like it was touching the slip ring but obviously not enough to work properly.
Obviously if I had paid attention to the weak and flickering battery light I would've known something was up a lot sooner, the battery light is for some reason on this dash cluster the worn brake pad light and I'd forgotten.
I don't know what caused the brush to break as the slip rings were fine however there was probably a mm radial play in the rearmost bearing which isn't good.
Ended up taking the alt off my '78 which is a Motorola unit. Cleaned the terminals, checked the brushes etc. 4.3 ohms on the field coil. (Old alt was 3.6, FWIW)

Works great, but! Back to having to blip the throttle to energise the alternator again (same happened with the '78 I removed this alt from). The old one, before it played up, wouldn't. Although I know many other diesels do it.

So, in this instance, the alternator itself is to blame....

__________________
1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD