1972 280se 4.5 alternator issue

[getzw]

my '72 280se 4.5 has a problem where the alternator does not seem to be providing proper charge to the battery. i have replaced the alternator with a new one and replaced the battery with a high capacity model. this seems to happen when i am doing city driving. has anyone put a more powerful alternator into one of these cars? i think the alternator cranks 35 amps. seems like a 60 amp alternator would work... thanks for the incites...

[aublutiger]

I have a 76 450sl. I was also having some issues with what I thought was battery/alternator problems but turned out to be a starter solenoid. But..in the process I learned to check the volts on the battery and this might help you. With the engine off, you should take a volt meter reading of 11-12volts. My battery was right at 13 when it was disconnected. I then started the car and took another volt meter reading...ended up being 14 volts...my resources said that with the engine running you should have an increase of 1-2volts.

[aublutiger]

One other thing...you may want to check for a parasitic charge...could be a radio or something that is zapping up the juice...I had that issue also and failed to mention it on my previous post. The aftermarket pioneer radio in my car was the guilty party...replaced it with a vintage Becker and solved that one...

[getzw]

should have indicated that a jump start always solves the problem. it fires right up with a boost.

[bwostosh]

Get a digital voltmeter on it, running volts of 13.7-14.2 is perfect, higher amperage alternator just buys you quicker time to charge after startup. If you need a jump to start, it may be a starter rebuild / clean-out time.
Been there with my 4.5's.