Alternator diode bad

[Jonrobinson84]

Anyone have info on fixing a bad diode on an alternator for 5.3? I saw a few items that might work. It still puts out great voltage but it drains the battery when turned off.

The inline plug looks like a great temporary fix but if I could rebuild the bearings and the electrical components I would like to do that.

I know replacements are cheap but let's talk about repair and rebuild in this thread

 

[rockola1971]

The 10SI is not hard to rebuild as far physically replacing the diode pack, regulator, brush holder assembly and bearings. The problem is during a typical home rebuild you wouldnt be servicing the rotor cummutator (is it out of spec? Where do you even find the specs for it?). The stator is Silver soldered in place so a standard soldering iron will NOT even come close to melting the silver solder because of its higher melting point than lead solder.
If you arent worried too much about the rotor commutator or stator being out of spec you can clean them up with some emery cloth or fine sandpaper and just take care of the guts (bearings, regulator, diode pack, etc.). Dont forget to break the pulley nut loose while the alternator is still installed in the vehicle with belt holding pulley tight.

 

[Jonrobinson84]

Sounds like you may have done this once or twice! Thanks for the pulley but tip! So the unit pictured is a 10SI? I was having trouble locating specs based on vin number.

Also do you happen to know if a good rebuild kit manufacturer?

 

[rockola1971]

Id your alternator type here: http://www.americanautowire.com/view-faq/how-to-identify-your-gm-internally-regulated-alternator/

You wont have a 10si alternator on a 5.3L. It would be more like a CS130 series or newer. What year, make, model is your Truck/Suv? That kit you have pictured wont work for yours. That is a kit that would have fit my 1985 S-10 Blazer back in the day. hahahaha

That alternator if it does have a shorted diode will ruin your battery. It could cause it to explode. When a diode is shorted it no longer converts AC to DC (an alternator actually makes AC). So your alternator would be feeding AC to your battery. That is not good.

 

[Jonrobinson84]

Guessing it's not a diode gone bad then. But with alternator unhooked and engine off it produces 12 volts when checked between negative terminal and alternator output.


My truck is a 2005 Yukon with 5.3. That page didn't seem to have my year as an option to see what alternator type I have.

 

[Jonrobinson84]

Id your alternator type here: http://www.americanautowire.com/view-faq/how-to-identify-your-gm-internally-regulated-alternator/

You wont have a 10si alternator on a 5.3L. It would be more like a CS130 series or newer. What year, make, model is your Truck/Suv? That kit you have pictured wont work for yours. That is a kit that would have fit my 1985 S-10 Blazer back in the day. hahahaha

That alternator if it does have a shorted diode will ruin your battery. It could cause it to explode. When a diode is shorted it no longer converts AC to DC (an alternator actually makes AC). So your alternator would be feeding AC to your battery. That is not good.

Guessing it's not a diode gone bad then. But with alternator unhooked and engine off it produces 12 volts when checked between negative terminal and alternator output.


My truck is a 2005 Yukon with 5.3. That page didn't seem to have my year as an option to see what alternator type I have.

 

[rockola1971]

Looking at the pics it looks like you have a CS130D series (bosch equivalent). You are reading 12v from the output stud on the back of the alternator (which the wires and regulator harness unplugged) ? The alternator isnt putting anything out if it isnt spinning while the engine is running.

It sounds like you need to isolate your battery drain problem. Disconnect the wire harness and the positive lead off the back of the alternator at night. Measure your battery voltage then the next day measure it again. Be careful with the red wire at the back of the alternator, it is hot 12v straight to the battery. You could have a fault in the alternator or it could be something else.