Alternator Rebuild

Here are the internals: a...        read full caption Here are the internals: a bearing for the front and rear, a diode, brushes with brush holder, a voltage regulator, and a rectifier.

The case can be clocked at...        read full caption The case can be clocked at 3:00, 6:00, 9:00, or 12:00. It’s important to mark both halves of the case with a punch mark, nail polish, or something else that will make it visible so you can put it back in the right direction when you finish the job.

Note how this alternator is...        read full caption Note how this alternator is being held in place by a vise. This works well as long as you gently clamp the pulley. Remove the four screws that hold the two halves of the alternator together. The electrical connections are at the rear of the alternator case, and the mounting tabs are at the front.

Alert, alert! The spacer-looking...        read full caption Alert, alert! The spacer-looking part is the stator frame (A). Make sure you remove it with the rear half of the case, or you could bend the stator’s wiring connections (B). Also, check that the stator winding isn’t burned or smells like it’s burned. It should have a natural copper color. If it’s burned, the alternator isn’t worth rebuilding. If everything is OK, unscrew the three nuts that attach the stator wire to the rectifier with an 11/30-inch wrench.

Three screws hold the voltage...        read full caption Three screws hold the voltage regulator in the alternator case. Two of them have nylon insulator washers, and the third is a grounding screw without insulation (indicated here by the arrow). It’s a really good idea to mark the location of the grounding screw before you remove it because if you put it back into the wrong place, the alternator won’t work.

Unbolt the rectifier and the...        read full caption Unbolt the rectifier and the stud at the back of the alternator. Make sure you don’t damage or lose the insulator.

Unscrew the nut that holds...        read full caption Unscrew the nut that holds the pulley. Tech tip: If it’s too tight to wrench off with handtools, take the alternator to a tire shop and have them use an impact wrench. After you’ve removed the pulley, take off the fan and the spacer, and the rotor should slide right off. If it’s rusted on tight, hold the alternator and give the shaft a few taps with a hammer. Also, before you reinstall the shaft, apply a thin layer of all-purpose oil (such as 3 In One) to the threads and only to the part where the front bearing goes through. The rear of the shaft can be wiped down with a rag or electrical contact cleaner.

To get the front bearing out,...        read full caption To get the front bearing out, take off the bearing retainer. You should be able to knock out the rear bearing easily. Now you can start reassembly. Install the new rear bearing, making sure you drive it in until it’s almost flush. If the bearing is flush, the shell will rub the end of the rotor shaft and dilute the grease, and the bearing will fail. The new front bearing is a drop-in replacement, although it may require a little tapping. Finally, screw the retainer back on.

Use a wrench to install the...        read full caption Use a wrench to install the new rectifier, tightening it as much as possible without breaking the insulator, and add the new voltage regulator and brush holder. Next, screw in the diode, ensuring you match up the insulator with your marking. Then reinstall the stator ring. (If the stator is brand-new, you may need to bend the terminals a bit to fit.) Finally, find the clock position and bolt the front and rear halves of the case back together.

Alternator rebuild. Rebuild. Alternator. Wait, don’t turn the page. Before you scream “Danger, danger, Will Robinson!” you should know this is one of the simplest repairs you can do. It’s important to have a strong alternator that functions properly, especially for low-speed ’wheeling, if your battery is weak, or if you’ve added extra lights or other electrical accessories.

The favorite alternator of many enthusiasts is either the inexpensive GM Delco 10si or the 12si with a built-in regulator, introduced in the early ’70s. (The “si” means systems integrated.) It’s popular because it’s user-friendly, a universal fit, readily available, and a bolt-in deal. You can swap the GM alternator into an early GM 4x4 or an early non-GM 4x4. Yep, it works great in a non-GM truck. And it doesn’t matter if you currently run an externally regulated alternator—the 10si and 12si bolt right onto the bracketry in early GM 4x4s and can be mounted onto most non-GM 4x4s. Unfortunately, owners of late-model 4x4s really can’t do this conversion. One of the biggest fans of this conversion is Mark Hamilton, president of M.A.D. Enterprises. He has a GM alternator in his Ford and swears by its reliability. We got our hands on a 10si model and turned to Hamilton to show us just how simple the rebuild is.