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Do-It-Yourself Projects
Alternator Check and Replacement
By Mike Bumbeck/
Printable version
Degree of DifficultyModerate
Estimated Time120 minutes
120 minutes
The good news is that determining which part of the system is doing its part and which part is a little tired or about to quit altogether is easier than ever. Many auto parts stores now have portable diagnostic equipment that can be wheeled out to sniff out in minutes what's going on with the electrical system. If the alternator has gone out to lunch permanently, replacing it is usually a relatively easy job. Follow along with the step-by-steps for some alternator replacement tips.
Step 1
Disconnect the battery negative. This is an especially important first step, as all the electricity for the entire vehicle goes through the alternator. A wrench or a screwdriver across connectors can quickly fry voltage regulators, expensive engine computers, and cause injury.
Disconnect the battery negative.
Step 2
On a v-belt vehicle there are usually two bolts holding an alternator to its mounts. One bolt or assembly maintains tension on the belts, and the other holds the alternator in place. First loosen and remove the tension bolt or assembly.
Bolts Holding an Alternator to its Mounts
Step 3
Next loosen the pivot bolt.
Loosen the Pivot Bolt
Step 4
Remove the pivot bolt. Remove the electrical connections and slide the pivot bolt through the mount. Remove the alternator. This is a good time to check and replace worn belts.
Remove the Pivot Bolt
Step 5
Compare the old and new alternators to make sure everything is the same. Transfer any connectors or bolts from the old to the new.
Compare Old and New Alternators
Step 6
Reverse the removal procedure, and install the new alternator.
install New Alternator
Step 7
Check the belt tension. A little under an inch of deflection is ideal. Too much tension will quickly destroy bearings. Better a slightly loose belt than one too tight.
Check Belt Tension
Step 8
On this vehicle, the alternator and the engine-driven accessories rely on one serpentine belt. A spring-loaded tensioner holds the belt in place. Slack allows the belt and the alternator to be removed.
Vehicle in which Alternator and Engine-driven Accessories Rely on one Serpentine Belt
Step 9
Start the vehicle and check the alternator output with a multimeter.
Check Alternator Output with a Multimeter
Step 10
Re-check the belt tension after about 500 miles. Adjust tension if required.
Re-check Belt Tension After 500 Miles
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