Several days ago I started to notice that the voltage was dropping below 11.5 volts causing the warning indicator to light up. Today it dropped even lower and at approximately 8 volts the total instrument illumination would go black. Revving the engine did not seem to increase the voltage. Before replacing the belt the alternator or something else, I would like to get some suggestions & opinions as to what the problem is. 1986 with 21k miles.

 

You have Zero Alt output. Worn Alt brushes and or Reg gone bad or maybe no power to the Alt or the belt is off

 

...or the wire between the alternator and battery has a problem. There is a fusible link in that wire, so check that out.

You should measure battery voltage at the alternator output terminal with the engine off.

 

Thanks guys, I'll check it out your suggestions.

 

Pull the alternator and have it checked at one of the auto parts stores close to you. Chances are the alternator has failed based on your seeing the volts drop from 11.5 down to 8. At this point your running off your battery.

 

Meter alt output. should be above 13.5 v.

 

I would say you were all correct, bad alternator. Rather than replace it, I decided to rebuild it, so I ordered a kit online. The kit included an "improved" rectifier, regulator, brush holder w/brushes & springs. Rebuilding included some soldering. I have rebuilt many of the older GM alternators, but none ever required soldering. I'm getting 14+volts at idle. Seems OK. Thanks Guys!

 

Where did you get a rebuild kit for this?

 

mfaria99, Google "1986 Corvette alternator repair kit" or just go to ebay. I bought my kit from s-and-g-repair in Urbana Ohio. The kit is listed as 86-96 Corvette but, will fit other GM vehicles with the CS130 & CS121 alternators. There are a variety of kits & individual alternator parts available. If you have an early 86 Vette, as I do, you should make this clear in your communications, as you will not likely see a rectifier that looks like yours, because the early rectifiers had a high failure rate, and the redesigned ones have a different looking heat sink. In addition, the shape of the four wire plug may be different, than the ones shown, But he should send a regulator that matches your plug. Describe your alternator accurately, in the buyer questions area, and you should have no problem getting the right kit. Installing the kit requires unsoldering the three stator leads from the rectifier just to gain access to the internal parts you will likely be replacing, then re-soldering them. Some YouTube videos show the cutting of the stator lead ends, I would not recommend this, nor would I eliminating the black plastic air deflector plate, as some other videos suggest. Probably more than you wanted to know. Good luck!

 

Thanks - I actually have an '85 120 amp, but the thought of a rebuild kit intrigued me. I'll poke around to see what I can find.

 

I think your 85 may have the earlier GM alternator, but there are kits available for it.