Truck Topics

The Tool Box - Changing your Alternator

Does your alternator charge properly? Does it run quietly? If the answer is no to either of these questions it may be time for a new one. How do you know what alternator you need? That is a question easily answered by asking your OEM dealer or a heavy truck parts store such as Parts Pro, Fleet Pride, or NAPA truck parts. You will need to know your truck serial number and they should be able to get you the right alternator.

If you are at home and it is time to change your alternator, take it off and see if you can find a rebuilder, as this will save you a lot of money. If no rebuilder is available, a new or remanufactured alternator is the only way to go. 

Most of the time when you get a new alternator it will come without a fan or pulley. These can be purchased new with the new alternator and the supplier may install these for you. If you would like to use your old fan and pulley it will require a hex (allen) wrench and a 15/16” combination end wrench. I have hex shaft sockets that fit on my 3/8" drive ratchet to make this process faster (another tool for the tool box).

Place the box wrench over the nut; insert the alan wrench into the end of the alternator shaft and turn, removing the nut. The pulley may need some penetrating oil to help it come off but should slide off. Remove the fan, if needed, and install on new alternator. There is a slot in the pulley and a key on the shaft of the alternator that must be aligned. Reinstall the nut and tighten. This can be done on the ground or on the truck before removal of alternator. 

To remove your alternator that uses a micro V belt, use your ½ inch drive ratchet in the tensioner, release the belt tension and flip the belt off the alternator pulley. Slowly release the tensioner and the alternator is almost ready to come off. Remove positive (red) cable from batteries (we do not want any arcing of power wire).

On the back end of the alternator there are two wires: one red or hot (positive) and one black ground (negative). Remove these wires using the appropriate tool (socket or wrench, whichever is easiest) noting their position on the alternator. There should be 4 bolts going through the alternator case holding it to the engine. Remove these bolts and the alternator will fall off, so be prepared to catch it. 

If necessary, remove the alternator pulley and reinstall on new alternator. Position the alternator and install the 4 mounting bolts, reattach wires in proper places, reinstall the belt, hook up battery cable and you are ready to go to work.

For V belt alternators, remove the battery cable as above, then loosen the mounting bolts (one on top and one or two on bottom) remove the belt from the alternator pulley, remove wires from rear of alternator, noting position on alternator, remove the mounting bolts and alternator is ready to come off. You may have to wiggle it to get it to come off. Change pulley, if needed, to the new alternator and install beginning with lower bolts. Install belt, install upper bolt, tension the belt with a pry bar, tighten top bolt, recheck belt tension, tighten lower bolt, reinstall battery cables, and you are ready to go.

If you bought a new alternator and did not return your old one as a core, try to find a rebuilder to get your old alternator rebuilt, as a spare is a good thing to have.

Till next time keep on charging!