How to Replace the Alternator on a Chevy S10by Jody L. Campbell; Updated November 07, 2017
Items you will need
Ratchet and socket set
Hand wrench set
Serpentine belt tool with 3/8-inch square drive adapter
Small pry bar
The Chevrolet S-10 pickup endured 23 years of production in the United States. Although a few different generational designs occurred as the truck matured, one of the mainstay features of this Chevy was the accessibility of the alternator. Alternators rarely fail, but access to the S-10 alternator made it an easy charging-system component to replace for the determined do-it-yourself mechanic. If your battery has drained as a result of the alternator failure, you should give your battery a full recharge, since the alternator only restores a portion of charge back to the battery.
Disconnect the negative battery terminal, and then isolate it so it does not come back into contact with the battery post during the alternator replacement.
Remove the air inlet duct, if applicable to your S-10.
Place the 3/8-inch square drive adapter into the serpentine belt tool, and insert it into the square drive on the tensioner pulley. Then pivot the tensioner to relieve the tension on the belt. Holding the tool with one hand, use your other hand to remove the belt from the alternator pulley. Do not remove the belt unless you're replacing it as well. Allow the tensioner to gently rest back into its applied position, and then remove the serpentine belt tool.
Remove the heater hose brace, if applicable to your S-10.
Locate the black- or red-colored cap cover on the back of the alternator, and pull it off with your fingers to expose the terminal retaining nut. Hold the inside nut stable with a wrench, then pull out the outer retaining nut with a ratchet and socket. Remove the terminal wire.
Pull out the two front alternator mounting bolts, then remove the rear alternator bracket bolt. Using a small pry bar, pry the alternator upward. Disconnect the remaining wire connections to the alternator, and lift it from the S-10. Use a small hammer to tap forward the spacer bushing at the front of the alternator mount, so that you can easily fit the replacement alternator into the mount.
Install the new alternator by reversing the procedure. Test-start the alternator when you have replaced the negative battery terminal. Be sure to charge the battery with a battery charger.
Before the second generation of the S-10 pickup featured the automatic belt tensioner and serpentine belt application, alternator replacement required a different procedure. Mounted to a slotted bracket, the lower mounting bolt of the alternator required loosening in order to pivot the alternator and remove the drive belt.
Be sure the serpentine belt is realigned and properly situated, with the ribs of the belt seated into the grooves of the pulley. The S-10 serpentine belt leaves little margin for error; so if it does not fit back onto the alternator pulley, it is most likely not aligned properly on a different pulley. This can happen when the belt is slack from being disconnected. Don't force the belt back onto the alternator pulley; otherwise you can damage it.
Be careful when using the serpentine belt tool. The automatic belt tensioner employs a coil spring to apply the correct tension on the serpentine belt. A slip could make the tool recoil and cause serious injury.
Remove all tools from the engine compartment and away from moving engine parts before trying to test-start the S-10.