Alternator help
 

I have an 83 300SD. The other day i was working on my car and a neighbor who is a mechanic, came over to say hello and he noticed a rattle sound that sounds like a spray paint bottle and said he thought that my alternator bearing was going out. A few days later, one of the belts started making a noise. A few days later the battery light came on. So before I go and remove the alternator, isn't there a way to check it?

When the car is OFF the voltage on the battery is 12.32
When the car is ON the voltage on the battery is 11.69

Also, there is a junction box where the alternator and the battery cables meet. Can't the readings here tell you if your alternator is doing it's job or not. see the attachment for a diagram of the junction box that i did real quick on word. The readings from left to right on the junction box are 0.0v, 2.37v, 10.75v, and 10.76v While the car is on.

Thanks guys, I very much appreciate your input.

Just to clarify...when you say the car is "on" do you mean running, or that the key is in the on position?

11.69 volts with the engine running is not a good thing, IIRC it should be something like 13.5 volts.

You are on the righ track. The voltage should go up with the motor running. From your symptoms of the noise, etc. it does sound like your friend is right.Sounds like not only are the bearings bad, but you have a bad diode(s) inside the alt.

Ron

Pull the regulator/brush assembly out ...that could be both problems.
It is a unit.

Wait !
 

Go look up old posts about the upgrade alternator as the stock one is only 55 Amp. , not really enough to keep the battery fully charged .

Pull the brush assembly out.

If the alternator still makes that noise with the brushes removed, then the bearings are bad and you have to replace the whole shebang regardless of weather or not the brushes or diodes are bad.

If the noise goes away, and there is obvious damage to the brushes, or they are worn down to the springs, then you might be able to get away with just replacing the brushes.


-tp

Is there an echo in here ??

For clarification
 

For clarification: the ON, means Engine ON.
Thanks everyone for your help so far.

So i've seen posts about removing the voltage regulator and that looks simple enough. How do you remove the brushes? Any photos? And how do you know if the brushes are bad?


Also, does anyone know if the readings on the junction box mean anything re: alternator? See the jpeg attachment on original post.

thanks,
Adam

"Pull the brush assembly out"

haha

Brush & Regulator Service
 

Adam ;

First ~ undo the ground cable ! .

Now , look at the back of the alternator , there's a big black plastic thing , that's the combination brush holder and voltage regulator , remove both screws and gently withdraw it , if one brush is longer than the other , they're shot .

Remove the fan belts and spin the alt. by hand , if any noise or vibration no matter how minute is felt , it's junk and must needs be exchanged for another , you don't say where you're at but there's _scads_ of them in all the self service junkyards across America , $30.00 each .

Lastly , when exchanging parts , never , EVER turn in the old dead part until the job is 100 % finished and working a day or two ! they'll charge you a few $ " Core Charge " but that comes back when you take in the dead part next week , have the receipt in your hand .

-Nate

Here is a picture

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1983@@1983&makeid=MB@@MB@@X&modelid=300%2DSD%2D002@@300SD&catid=F@@Engin e+Electrical&subcatid=F4010@@Voltage+Regulator&applicationid=000272329&mode=PA

That year also had external regulator on early chassis, so you will know when you remove the brush holder.
Pic is the reg/brush combo. Click on the pic and it will zoom out for a good look at what the brushes look like on a new unit for comparison. If the brushes are gone, you will see it and that can be both the noise and charge problem.
Simple to replace , and a common wear item.........

"First ~ undo the ground cable ! ."

Absolutely correct. Good point. Always remove the negative battery cable when working on anything with a belt on it. Also, you can fry diodes by inadvertently shorting the alternator when working on it. Been there, done that.


-tp

Clarification
 

Hey guys, thanks for all the advice. I will pull the volt regulator out tomorrow and see how that goes.

For clarification though: Does any one have any ideas on the JUNCTION BOX? Can the readings on it tell you anything about your alternator. The car engine was ON when i took these readings. It is under the hood on the battery side and your battery cables lead to it.

see diagram

Junction Box
 

What diagram ? :confused:

Yes , this is a good place to do charging and voltage tests .

The connectors there often get loose or corroded so it's wise to remove the screw , polish the eyelet connectors with metal polish (never , EVER sand an electrical connector !) then coat with bearing grease before re-installing , do one at a time so you don't mix 'em up .

Diagram
 

Oh. i was referring to the diagram in the original post at the top of this thread. Here it is.