300 SD Alternator?
 

My battery went dead. The local gas station tested my electrical system. They showed me some machine that said my alternator was putting out 11 or 12 volts. They said it should be 13, and that I need a new alternator, not a new battery. Does this sound right? How much does an alternator cost (1984 300 SD) and how many hours labor to install it?

Details
 

The car seems to run fine. It has been over 100 degrees for the past few days, so I had the ac on driving around town. Everything was fine until I came out of a store and the battery was dead.

Bosch rebuilt alternator for an SD is about $130.00 plus 75.00 core from Fastlane ,it's a straight foward DIY job,no tricks that I remember.That should disspell any rumors that MB parts are expensive......
William Rogers......

Install Alternator
 

How many hours labor?

Does the battery light come on when you turn the key to position 2? If so, and it doesn't come on when the engine's running then I don't think the alternator's bad. It might be a bad voltage regulator which is considerably cheaper than a new alternator.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Alternator is pretty straightforward DIY job. No more than an hour.

DIY?
 

What is DIY?

Dirty,injury,yelling!
William Rogers.........

Do It Yourself.
But William is right about Dirty, Injury, yelling also.;)

Scam
 

I had my car checked out by someone else. The alternator and voltage regulator were fine. Only problem was a very old battery. It looks like the first place I went tried to sell me stuff I didn't need.

I don't see why they would scam you on an alternator and not on a battery. It could be that the brushes on the alternator are bad and are connecting intermittently. I have never changed them myself but am told it is just a couple of screws and a 15 dollar part.

Money
 

They tried to sell me a rebuilt alternator, installed, for $275, and they knew the price (parts and labor) without checking. I think there are cheap alternators for less than $75. That means $200 for changing the part. On a $105 Interstate battery they might make $50.

Jacob:

Although yours is a 126, my 140 just had the job done. If you read from the multi-meter that the current reads below 14.5 with engine running, your alternator is not pushing enough juice to charge the battery. Without the engine running, the battery should read at least 12.75 volts. Mind you, you should have all "normal" electronics turned on to test the alternator juice, i.e. A/C, radio, lights, .........

One more thing, you can change the "small" voltage regulator on the alternator to isolate the problems. Many have responded that the voltage regulator will fix the issue which is a small investment to pay. I have seen the regulators on e-bay.

hope this helps...

Alternator regulator replacement instructions can be found here.

If that doesn't do it (cheap) keep the new regulator for use later. FastLane has them.