Replacing a 55 Amp Alternator on an M110 Engine

[Brian L]

Greetings All,

I hope everyone is having a great summer. Just thought I'd take a few minutes and document the replacement of a 55 amp Bosch Alternator on my 1973 280 (w114) with an M110 engine.

I purchased the car a few months ago and the PO failed to tell me that the charge light was on when the engine was running. He was forthcoming about the Ac fan which was not working properly and with a few other things that needed repair and/or upgrading, I decided that going to a larger alternator was necessary. I've had really good luck with "one wire" alternators purchased from Motor City Reman (I'm from the Detroit Area but not affiliated with them in any way).

I took the unit to them, they tested the old unit and indeed confirmed it was dead and we matched up a housing that was very close which wound up being from a GM truck engine. I can get the part number if anyone is interested and ultimately purchased a 135 amp alternator. I like the new unit because as you can see the back of the alternator is covered in plastic whereas the Bosch unit had it's "private parts" hanging low and exposed to the world.

A few modifications that I found to be pretty straight forward were required. First, about a half inch of the back bottom mounting ear on the alternator had to be cut in order to get the correct spacing using the existing bracket. The pic shows me using a vertical mill, but you could easily use a hand hacksaw, sawsall, dremel tool, etc. as the housing is aluminum

Then the existing top spacer from the Bosch unit was cut down to about an inch in length. Once you get the new alternator in place using the bottom mounting ear, you can line up the pulleys and mark length of the top spacer that needs to be cutoff. I had to add a bushing to the front of the top mounting ear, which I machined, however you could actually use a 1/2 inch galvanized pipe nipple from Home Depot and just cut to length.

Once the unit was mounted, I ran #4 cable directly from the alternator to the battery lug on the starter. You could actually run from the alternator to to the battery on these one wire units, but I always wire directly to the starter, that way if I have a bad battery connection or a dead short across the battery the engine will still run.

Last thing I did was purchase a low voltage sensor from Ron Francis Wiring for about $35.00 and took the blue wire from the charging idiot light on the instrument cluster and connected it to the sensor as it previously went to the voltage regulator on the back of the old Bosch unit.

That's it. Fired it up and got a nice steady 14.6 volts at the battery.

Hope this info helps. Oh yeah, the alternator was around $120.00, so the whole job, not including my time was around $175.00 including cables, connectors, etc.

[Jub]

Hey Brian,

Nice job. But just trying to figure out why you didn't just order the part that fit? Are you saying that you wanted to get more amps...?