Rebuild an alternator
These days alternators are getting more and more costly (up to several hundred dollars depending on the application) while intermediate rebuild kits are very inexpensive and once you've done it, very simple to do.
Assuming the alternator didn't burn up electrically (windings melted down) these simple steps will net you a very reliable operating alternator and save you about $100 bucks in the process.
 Rebuild your alternator
If you plan to rebuild your alternator, some easy steps to a DIY project are below.
 Types of alternators
Here’s three different GM alternators, on the left is the 10DN which uses an external regulator. In the center is the internally regulated 10SI (Systems Integrated) used from the later ’70s. The serrated end that makes it easy to spot. On the right is the CS130.
 CS130D alternator
The connector is usually labeled PLFS or PLIS. The only wire used is the L position, it's connected to the dash light. Do not connect this to a 12 V source, as that will damage it. If a dash light isn't used, install a 50 to 80 ohm, 5 watt resistor in series to a switched power source. On connectors without any markings as to which wire/terminal is which, use the third position counted from the large end of the connector for the dash light or resistor.
 Removal and clean up
- Disconnect the vehicle battery. If you have a charger put it on charge during the rebuild. This will help to improve battery life and minimize the load on the fresh alternator after rebuilding.
- Remove the alternator from the car and clean it thoroughly.
- Using a scribe, witness mark the case halves so you can get them indexed properly when you re-assemble it. It can go 3 or 4 different ways.
- Remove the through bolts so you can separate or halve the cases.
- Remove the brushes, brush holder/followers (depending on the alternator).
- Remove the rear bearing, clean out the bearing cavity of any dirt or grease.
- Remove the bushing (if applicable)
- Remove the regulator and install the new one. Make sure that any grounds that may be used internally are clean shiny metal to assure good contact.
- Remove the rectifier diodes or diode assembly and install the new one(s). If you have to solder use good techniques, clean the metal connectors, use 60/40 lead/tin solder. If soldering the silicon diodes do not overheat the diodes, 7 seconds at soldering temps is a safe limit. Better yet use clips to pull the heat away from the diode body.
- With a fine emery or crocus cloth, burnish the brush pickups or (slip rings) on the rotor assembly until smooth and shiny. Emery dust is conductive so clean up your work when done.
 Installation and inspection
- Install your new bearing, but before you do, get a SMALL sharp punch and carefully put a dimple in the race each 1/3 rd the way around. One may use a dab (small dab) of epoxy to accomplish locking the bearing race. This will prevent the race from spinning in the case. It will be a tiny bit harder to put the cases back together, you might have to tap the halves with a rubber mallet.
- Install the bushing (if applicable). Lubricate the bushing as required.
- Where the brushes are, at the rear end bell, there should be a small hole that goes through to them. Insert a #40 drill bit or heavy paper clip with the brushes fully compressed into their holder. This will hold them off the slip rings while you insert the rotor into the end bell. Remember to remove the paper clip or drill before reinstalling the battery or a short could occur while removing the drill or paper clip.
- Before reassembling the end bells to the body, inspect the stator windings. You are looking to make sure there is no worn insulating paint, aka "Glyptal". Also, where the windings terminate, check that there is no melted or splattered solder, and no cracked solder joints. If needed, ohcheck the resistance with an ohm meter, but these usually last practically forever.
- Align the witness mark you scribed into the body during dis-assembly, install the end bells to the body and properly 'clock' it for your application. Be sure the end bells are straight, and (if needed) gently tap the bearing half end-bell with a mallet. Secure with the bolts.
- Lastly, spin it up by hand, in both directions, and ensure it spins free and quiet. Inspect the front fan blade for damage, and reinstall on the car.
- Check your wiring to assure correctness and reconnect the battery. Start the car and using a digital voltmeter check the voltage at the battery terminals. It should be about 13.6 - 14.0 volts with headlights on.
 Inspect the hardware
If you notice white powder on the brackets or hardware, you have electrolysis going on (mounts are aluminum and hardware/engine is steel... what were they thinking??) Remove and media or water blast them. If you are a "stickler" install a copper braid strap from a good ground on the alternator to a good ground on the engine block. This will assure good electrical performance and eliminate mounting brackets from being important to the electrical ground path.
Get some electrical bonding paste for aluminum wire and coat the bolts and mounts, anywhere they touch steel...
That should give you a much better unit than you can buy over the counter... that will probably out live the car.
 Mounting and rotation
An alternator will generate current in either direction. But what can hinder this is the alternator fan function.
The alternator cooling fan is designed to pull air into the back of the alternator to cool the diodes/heat sink located there, then the air is exhausted out the front. Spinning the fan backwards will pull air (less efficiently) in the front and push it back through the alternator until it reaches the diodes/heat sink then exhausts out the back. So IF the fan is directional, it will be more efficient in one direction than the other.
Whether or not the loss of the fan's efficiency is a matter for concern will depend on how hard the alternator is worked, and the underhood temperature and air flow around the alternator in the vehicle it's in now.
In many cases there will not be an issue unless there are higher than normal temps under hood and/or the alternator duty cycle is extreme. But if this were to be a concern, the fan can be swapped for one that gives the correct air flow or one that's "bidirectional" can be used instead. A bi-fan will have basically straight blades radiating out and won't have any fan blade bias as to direction like a directional fan has.