My alternator is dying, it is putting out full voltage but only 25 amps. Does anyone have any experience with rebuilding these? What about parts? Bearings, brushes, diodes? Thanks Bill

 

Mine just died. For $85, I'm getting a rebuilt unit with a one year warranty. For that kind of money, It's probably not worth the hassle of rebuilding it yourself. Have you priced a rebuilt unit locally? You might be surprised.

 

If the voltage is there, then the current must be there.
Remember Ohm's Law:

Voltage=current X resistance

As the equation indicates the voltage is made from the
current. Where are you measuring the current? You
should have your ampmeter sensing the main line
from the alternator and NOT sensing the battery leads.
This is a common error made by many shops and dealers
who sell alternators when the problem is elsewhere.

Also, you'll never (unlikely) get a good rebuilt alt. for $85.
A good OEM regulator alone at a rebuilding shop cost is $50.
The alt. needs a new rotor and bearings.

Don't put junk parts in a good Porsche!

Good Luck
Loren
'88 3.2

 

I have a red light come on when I start my 74 911 w/ S Gauges.
The light is on the oil temp gauge.
Anyone know exactly what this is telling me and what I should watch for? I think it is checking the alternator and comes off when it is done.

 

No experience with rebuilding one, but I did get a rebuilt alternator and install it. The job isn't very difficult - there are good instruction on Pelicans site and it only takes an hour or two. Good time to clean up your fan and housing while you're in there. Make sure the VR is replaced too ($50), good insurance.
As for the red light on the oil temp gauge... I have a newer car so it may be different. The red oil light is basically an idiot light, comes on for a second as the car is started until it senses enough oil in the engine. If it ever comes on while driving you've got problems - pull over and shut down the engine until you can confirm its not leaking badly.
There is also an alternator light that comes on until the alternator is making some req'd voltage. The light should be on with the key in "on" and then go out shortly after starting the motor. A dim or fully lit alt light tells of possible bad diodes, bad grounding, or a failing alternator/volt regulator.

Cheers,

 

Thanks for the great replies! Here are some more details. I had the car in for some work, during that time the alternator was checked. I was told that I needed a new alt. as ot was only putting out 25 amps. When I start the car idiot light comes on than quicky goes off, it never comes on or burns dim when I'm driving. What is the deal? Mechanic trying to screw me?

Bill

 

Check my post above. The shop may not be testing the alt.
properly. As long as the light comes "on" and then goes "off"
when engine starts, the alt. is probably OK.

You didn't indicate a car type. Different car alt.s have
different failure modes.

Good Luck
Loren
'88 3.2

 

The car is an 1987 911 Carrera Coupe.

THANKS!
Bill

 

What year is your 911?

 

1987

 

Problem solved. The alternator finally died. I've removed it and am having it rebuilt.