Replace The Alternator on a GM S-Series Trucks

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Changing or upgrading the alternator on an S-Series truck sometimes requires a little bit of modification (like re-clocking). Some need to be rotated, others just bolt right in.

This article will cover installing a new alternator, and what it takes to re-clock/rotate the housing on a typical alternator like the Powermaster unit I purchased.

The Syclone uses a typical GM internally regulated 3 wire alternator used on many vehicles, so this guide will loosely apply to many vehicles, certainly all of the S-Series clan (Chevy S10, Blazer, GMC Sonoma, and Blazer).

  • Typical Socket and Ratchet Set (my favorite are these GearRatchet Sets)
  • My Powermaster used a 15/16" socket for the fan.
  • A large Screw Driver

Disconnect The Battery


Be sure to do this first, you'll be dealing with hot power cables and you don't want to cause any damage to the car or yourself.

Disconnect The Alternator Wires


The 3 wire alternator essentially has 3 wires connected to it. Note that generally the power output post may have several wires feeding power to various accessories around the vehicle.


Disconnect the quick disconnect connector. This connector holds 2 of the 3 wires used on a GM 3 wire alternator. One is the field wire that energizes the alternator. The other is the sensing wire that is used to determine voltage output.


Disconnect the main power post, there are usually several o ring connectors sandwiched under a nut.

Remove the Serpentine Belt


The belt is under tension, so we'll have to remove it before we unbolt the alternator.


Using a long breaker bar (longer makes it easier to hold if you're doing this alone) and the appropriate sized socket, rotate the entire tensioner counter-clockwise.

Note that the bolt itself won't rotate, the whole tensioner will swing up, giving you slack in the belt to remove it from the alternator pulley.

Unbolt the Alternator


Remove the inner bracket bolt.


Remove the rear housing support bolt. Note that this bolt is important to properly support the alternator.


Then the outer accessory bolt. This is the last one, you should be able to remove the alternator now.

Re-Clock the Alternator Housing


This isn't necessary for all alternators, but for whatever reason, the Powermaster alternator I bought needed to be spun to bolt in correctly. You need to be careful doing this because there are several parts inside the alternator that are sensitive, and a total pain to re-install.


Start by unbolting the center bolt that keeps the pulley and fan on. To accomplish this I used a screwdriver to keep the fan in place.

Image 2112 from Replace the Alternator on a GM S-Series Trucks

Once the fan and pulley are off, remove the 3 bolts that hold the two halves of the housing in place. Be very careful not to separate the housings now.


Now slowly and carefully rotate the front housing to the desired location. You may need to separate the housing slightly, but typically it's less then a few millimeters. The picture below is much further then you'd typically have to separate them.

The reason you don't want to remove the front housing any more then you need to is that the brushes are spring loaded, and held in place by the front housing. If you pull it out too far, they'll be a real pain to re-install.

Re-install the Case Bolts and Pully


Simply re-install the 3 case bolts, pulley, fan, and washers that you took off.

Image 2121 from Replace the Alternator on a GM S-Series Trucks

Installation Is a Breeze


Now that you've taken it all off, you simply do the same in reverse.

Install the 3 Mounting Bolts


Make sure you install all 3, the rear housing bolt provides support that will keep the case from cracking under the pressure from the serpentine belt. My Powermaster required a few spacers here fro some reason.

Re-Connect The Wires


Re connect the power accessory wires.


Re-connect the field and sense wire connector on the side.

Re-Install the Serpentine Belt


Make sure the belt didn't slip off any of the other pulleys, turn the tensioner again, and slip the belt up over your alternator pulley.

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