Lenny,
I know GM has used rubber mounted harmonic balancers for years and so have many other manufacturers. However the pullys are bolted directly to the crankshaft hub and the balancer which is just a heavy weighted ring is mounted with rubber to hub or is part of the hub. I hve seen a few of these fail, but have seen or herd of a lot of pullys mounted in rubber comming loose when the rubber gives up.

Paul

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84 500 SEL (307,xxx miles)