How to rebuild a vintage General Motors alternator – Rocky Rotella @Hemmings

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When a hobbyist opens the hood of his or her vintage vehicle, the alternator generally isn’t what’s admired most. In fact, short of a charging system issue that forces action, the belt-driven voltage generator is so reliable that it can operate inconspicuously for years without maintenance. Nothing underhood is truly maintenance-free, however, and our Pontiac’s alternator proved just that. It wasn’t a charging issue that drew our attention. Instead, a persistent chatter at idle speed indicated something was amiss. A cursory check revealed that an internal bearing was beginning to fail, and without swift action it could leave us stranded.

For our ’76 Firebird’s 80-amp 10SI-series alternator, bearing replacement requires removal and disassembly. After disconnecting the battery and removing the alternator’s drive belt, electrical connections, and mounting hardware, it simply lifted out and away. On the workbench, we used a 15⁄16-inch wrench and 5 ⁄16-inch hex-wrench to remove the cooling fan retaining nut and lock washer, the fan, and its shaft spacer.

Our ’76 Firebird was originally equipped with a 10SI (or System Integrated)-series alternator developed and produced by GM’s Delco-Remy division in a variety of sizes and output ratings. While remanufactured 10SI alternators are typically stocked at local parts stores, we find originality important and decided to completely disassemble our Firebird’s original 80-amp unit and replace its shaft bushings. That then afforded us the opportunity to replace the internal electronics, essentially resulting in a complete alternator rebuild. Follow along to see how we did it.

A 3⁄8-inch socket was used to remove the four through-bolts that secure the alternator case halves together. The alternator assembly was then separated by lifting the halves apart.

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Categories: alternator, general motors, Hemmings, Tech 101

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