alternator question

[speedracer]

I thought maybe my alternator was going bad but after checking it with a volt meter it's putting out 12-14 volts.  Then I happen to look up and saw it was alittle below 10 then 8 then my radio quit and I started trying to get home ASAP!  Then right before I pulled in it jumped back up to 12 volts stayed there for 10 minutes then back down to below 8 volts!  Could a old corroded battery cable do this?  I took the unit off and brought it over to the speed shop, they say it's putting out 14 volts and not to worry!  I got the altenator from Jegs its a one wire type.
Any suggestions??
Thanks John

[Bruce Dorsi]

I had a relatively-new, chrome (aftermarket), one-wire alternator fail on me one night.  ....I had to drive home on the battery.

Turned out that the rear bushing in the alternator had been over-greased when the unit was built, and the excess grease got on to the slip-rings of the rotor, insulating the brushes from making electical contact.]

After I cleaned the brushes and slip-rings, I sparingly re-lubed the bushing, and had no further problem.

Your problem may be as simple!

[speedracer]

I had a relatively-new, chrome (aftermarket), one-wire alternator fail on me one night.  ....I had to drive home on the battery.

Turned out that the rear bushing in the alternator had been over-greased when the unit was built, and the excess grease got on to the slip-rings of the rotor, insulating the brushes from making electical contact.]

After I cleaned the brushes and slip-rings, I sparingly re-lubed the bushing, and had no further problem.

Your problem may be as simple!

hey thanks Bruce, ya know that could be, correct me if I'm wrong but the wire from the alternator goes to the positive battery post and thats it right?  I was thinking maybe the ground on the battery might be bad as in corruded cable so I installed a new one with no results.  Now the mechanic says its reading 12-14 out of the unit but my cheapie gauge reads around 10 volts.  And of course if ya drive more than 30 or 40 minutes the battery gets run down.  thanks!