I read in the forum that replacing an alternator on my '71 280sl should take about an hour or so, but it took me 3 days (hence the title), so I thought I'd share a couple of details with others who want to try.
It was supposed to be easy because I have an a/c unit, so the bracket is at the top of the engine.
First, note that you will need an impact wrench to get the pulley off the old alternator so that it can go on the new one. I recommend getting the new alternator from a local dealer who can take the old one in trade and switch the pulley to the new one. Also note that when you switch the pulley, there is a little nub on the shaft of the new alternator which seems to be too big for the slot in the pulley, but the nub is actually removable and can be adjusted for a snug fit.
Incidentally, I upgraded the alternator from 35 to 55 watts. I had a bosch AL64X and I got a bosch 002 154 4602 80 (this was for my '71 280-sl), and it fit perfectly once I figured out that the nub on the shaft was adjustable.
Disconnect one of the battery leads before you start.
First, open the radiator reservoir to release pressure, and disconnect the hose from the reservoir to the radiator. This will give you more room.
Also, unplug the wiring harness from the alternator so you can see the nut on the back of the long mounting bolt (there's a small retaining clip to loosen first), and also disconnect the b+ lead.
Then, loosen the two mounting bolts so you can turn the belt tensioner, and loosen the belt tension so the belt becomes pretty limp. Then, you can remove the top mounting bolt and slip off the belt, and finally remove the bottom bolt and the alternator (note that the bottom bolt has a nut on the back).
There's a spark suppressor on the back of the old alternator, and you can switch that to the new one after you use an impact wrench to loosen the pulley bolt and swap the pulley.
There's a trick to lining up the holes when putting the alternator back on. You need to get a a couple of bolts approximately the same diameter as the long mounting bolt, with one a couple of inches shorter and the other a little longer. This is because it's kind of tough to line up mounting holes of the new alternator with the holes in the bracket.
It's much easier to line up the bracket and the alternator's bottom hole from the back. So, for starters, I loosely attached the top of the new alternator, and then I wiggled it into the bracket and felt around with a small screwdriver through back hole of the mounting bracket until I found the back mounting hole of the alternator. Then, I removed the screwdriver and tried to stick in the short bolt from the back (more wiggling). Once the short bolt found its way into the alternator, I removed it and stuck in the extra long bolt, which eventually (with a little more wiggling) found its way through the alternator and then finally stuck its nose out of the front of the mounting bracket!
Once everything is perfectly aligned, you insert the actual long mounting bolt in the front mounting hole and pull out the long test bolt as you push the mounting bolt through.
Then, reconnect the harness (and slip on its retaining clip), reconnect b+ (you can use either terminal), tighten everything up, readjust the belt tension (1/2" when pressed with thumb), reconnect the battery and the radiator overflow hose, and then start 'er up! Hopefully, the little red battery light will go out now!
Bruce
