|Delco-Remy 12SI Alternator|
For more information on identifying alternators, this article by Mark Hamilton is very well done.
Parts and ToolsPictured below is a classic Delco (Delco-Remy) aka GM, Volvo, Saab, Jeep alternator, model 12SI, along with the tools you'll need for the rebuild. From left to right: hex key set (smaller hex key for holding brushes), needle nose pliers, combination wrenches, 1/4 drive extension, socket, and 1/4 drive wrench for removing housing bolts and internal bolts, flat head screwdriver to pry apart housing, and permanent marker.
|Delco 12SI Alternator and tools for rebuild|
|The alternator kit I used from Autozone|
Note: P/N GMA02 is for the 94A version. Another example is the Amazon alternator listed at the top right of this article (should work with the lower current 12SI).
Note: You might want to click the compatibility charts to make sure it will work with your vehicle.
Opening the Alternator
You'll start by marking the housing so you know how the two halves are supposed to go together. Called "clocking", these alternators can be put together so the mounting bracket on the front half and the field plug on the back half can be oriented at any position.
After marking, remove the four long hex head bolts that hold the two halves of the housing together using the right 1/4"-drive socket, extension, and ratchet wrench.
|Remove hex bolts from rear of alternator to begin opening the case|
Next, use a screw driver to pry the housing halves apart at the pry points shown and pull the case halves apart.
|Pry alternator halves apart with a screwdriver|
Now that you've got yourself two halves of an alternator take the back half and stare into it and you should see something very similar to the following.
|Back half of the alternator with diodes, brushes, regulator identified|
Remove Regulator and BrushesStart by taking out the the bolts holding the regulator and brush housing and remove both. Throw away the regulator but keep the brush housing.
|Remove the 3 bolts holding the regulator and brush assembly|
|Old regulator, left; brush housing, right|
Match the old springs inside the housing to one of the new springs in your alternator repair kit. Install the springs in the housing and throw away the old ones.
Find the long thin piece of metal wire included in the repair kit. It holds the brushes in place until the alternator is reassembled.
There is a hole in the back of the alternator that you can use to pull this wire out, once you've reassembled both halves. If you don't do this, the brushes pop out of the housing and you can't insert the shaft.
Install the new brushes in the housing and force them into the housing until you can slide the thin metal wire through the hole in the housing and brushes.
|Retaining brushes with thin metal wire provided in kit|
Replace the Diode RectifierThe diode rectifier pictured below is removed by taking out three additional bolts.
|The diode rectifier on the left is held by three remaining bolts|
Replace the Regulator and BrushesNow install the regulator and brush housing along with the threaded rod resistor thingy with the three bolts that hold it in place. One of those three bolts also holds down a leg of the diode.
Look at the back of the alternator and be sure that you can see and grab the thin wire holding the brushes.
Grease the Rear BearingThe rear bearing on these alternators isn't sealed. Unless it's shot, throw some grease on it. I used axle bearing grease.
|Pic 4. Brushes held by wire, greased rear bearing, final regulator bolt|
Reassemble the Alternator CasePut both alternator case halves together, aligned with the mark you made, and install the rear hex head bolts that hold the case halves together.
Replacing the Front BushingOne thing I have not attempted is to replace the front bearing. However, I have had one of these go out before and they are included in the rebuild kit.
My educated guess is that the process is as follows: Use an impact wrench to remove the pulley and cooling fan, and slide the shaft out through the back of the housing. Use a bearing/seal driver to punch the bearing out. If I get around to doing it myself I'll post up definitive instructions.
Congratulations!Congratulations! You're all done and you saved yourself a pretty good chunk of change on a new alternator by spending a little time. This rebuild is pretty hard to get wrong so there's a good chance when you test it, everything will be a-ok.
If you do a lot of back country driving, the last thing you want is to have your alternator die on the trail so how about keeping a spare rebuild kit in your getcha-back-box? Or get a broken alternator from a friend for free and rebuild it as a spare.
Thanks, hope this article helps! If so, please share it with your pals.