I have a 1977 280E that when I do not drive it for more then a couple of days the battery goes dead. My mechanic sayed that he was getting a reading of 9 at the alternator. I know that the regulators can be replaced. Could this be the cause of the low reading. The Alt belt is fine and the battery is new. What is the procedure for replacing the regulator?

Thanks

Bruce

I don't know what this means. We use an amperage drainage test to check the amount of current the car is consuming when not in use. If it is higher than 35MA after 5 min., you can bet there is a consumer not switching off.

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Does your mech mean nine volts total alternator output? If so, then start the engine and disconnect the battery and then measure the voltage at the battery terminals and see what you get. If it won't run w/o the battery connected, then your alternator is rapidly heading south (or maybe already there). The car is old enough to be entitled to a new alternator, don't you think??

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Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE

re: "...If so, then start the engine and disconnect the battery and then...."

Oh, no! Don't do that! Don't even think about that -- ever!
If you ever have an engine running and suddenly disconnect the battery, the spike will fry virtually every electronic system (radio, fuel injection processor, etc.) in your car -- instantly -- as well as destroy your alternator's diodes, so if your alternator wasn't bad before this test, it will sure to be toast after it.
You may be able to get away without damage by doing this on a lawn mower, but NEVER on a car.
I sure hope that I caught you with this warning before you tried this.

Well, Ken, I have to say that I've done this a number of times on many different vehicles w/o any ill effects. (including both of my 300e's, the bimmer and a couple of Jeep Cherokee's that I've owned. I realize that the battery acts as a capacitor to absorb alternator output fluctuations, but, in most cases, if the alternator is charging with no load other than a partially or fully discharged battery and maintaining at least 12 volts, there should be no inductive "spikes" generated by disconnecting the battery, especially if the alternator is not producing the minimum threshold voltage necessary to get the regulator to clamp it's output. This is not a recommended servie procedure, but it does work. When you jump start a dead or nearly dead battery, you are essentially doing the same thing. If you have a good alternator and regulator, it will clamp output voltage to avoid self destruction as it wi6ll see the dead battery as a huge load once you remove the helper from the circuit. It's the alternator that keeps things humming when your battery is dead.

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Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE