Dramatic alternator failure, or how my 1987 300D left me stranded..
 

Driving on the interstate at approximately 75 mph, I felt a jolt, heard a loud pop followed by a whoosh and the battery light and I think the antilock and SRS light come on.

I immediately thought that I lost either just the alternator or the serpentine belt. Luckily I was right by an exit, so I gunned the car and cut between teo semi trucks and off the freeway.

I shut off the engine on the off-ramp, but the temperature still got up to nearly the 120C mark (!!!). I parked on the offramp, popped the hood and the belt was in 2 pieces. I pulled it out of the pulleys, let it sit for a couple minutes and let the aux pump drop the temperature about 5 degrees before starting the engine for another 5 seconds to bring me to the shoulder of a country road. I called someone to bring the trailer down. I left the key on, pulled the temp down to 40C before resigning myself to waiting for the trailer to arrive.

The alternator pulley is totally loose...it will wobble about 20 degrees off its axis. I think the shaft broke, bearing may have siezed.

Anyway, here I sit...let down by my always faithful 300D. Back to driving the Saturn, I guess!

Only time I was ever stranded by an MB diesel was an alternator going out...on a 92 300D.

This is your opportunity to upgrade to a modern high output alternator.

Man, that stinks! Sorry that happened. Luckily nothing super major to fix if it's the alternator, right?

I had a very similar thing happen on my Mazda years ago; alternator seized. Pretty much without any warning. It snapped the serpentine belt, left me stranded without a working water pump, much like yours. New belt and alternator, was up and running soon after.

I see this mentioned constantly on this forum. Unless you're running zillions of lights or an 800w stereo, what the heck do you need more output from the alternator for?

Realistically, it's just brownie points.

If you do short trips and you have afterglow yes it makes a noticible difference. Later alternator designs are small, lighter for the same output. Then you can get into really modern designs with anti stall, load response and over running pulley for that smooth as **** from a duck's ass belt drive. A larger alternator will also extend the life of your battery by quickly rechaginging it after each start.

Put on a 115a alternator from an om606. Less stress on your battery and charging system. Those old 70a alternator are dinky. If you find an e420, or e430 at the yard they also have 115a alternator.

Unfortunately it is not unknown for the pulley nuts to come loose even on the older models.

Since 1968 I have only had that happen one time on US made Vehicles and have never hand anyone tell me that same happend to them. Don't know if it is a Bosch issue or not.

I always carry some 1/4" nylon rope. One use is to tie a loop to turn just the water-pump pulley. I did that when my alternator bearing seized, squealing the belts. Trick is to tie a barrel knot (like fishing) and get the rope taught. If you get the diesel started, you won't need any more battery until you get home, unless driving at night. Hitting 120 C for a short time will not hurt the engine. Indeed, the temp sensor in my 1984 & 85 300D's will show excessive temp from just an air pocket by the sensor.

I wouldn't mind upgrading slightly to a newer style internal fan alternator, but I'm not too worried about output, as the car is all stock -- are there any newer style alternators that are plug and play? I will probably add the INA clutched alternator pulley as well to smooth out the belt a bit.

If I recall correctly, I will not be able to put the replacement belt on to the pulleys without removing all the mechanical cooling fan bits (I hope I'm wrong?) so I will probably replace the water pump and radiator as preventative maintenance.

I'd also probably like to upgrade the water pump pulley to the smaller one from the OM606 for increased cooling capacity -- summer is coming. Any tips on any of the above? I replaced the tensioner, idler, fan and clutch (with the plastic version from the later diesels) in 2015.

Good idea. I did that to my 124.

Just be sure to get the wiring harness and the distribution block from the donor too. The existing harness in the 87 has a plug in connector (that can go weak) while the larger alternators have a bolted connection which is much more reliable.

The extra capacity is helpful when running with heavy load, like the lights, wipers, blower, rear defrost all going at once, and you're still trying to top up the battery from the glow and start cycle.

Think those 70 amp alternators are wimpy? Try the old 35 ampers in the 220 D's!

Any MB alternator up

Any MB alternator up around the year 2000 is a a bolt on affair.