When it rains it pours!

Take the belt off and start it up. Dont let it run long because you will not be circulating coolant and it will heat up fast.

If the fan are out of balance it will cause a bad vibration,It was a first hand experience on my part. Just like Stangmen393 said,just take the fan off and start up the car,you will know right away if thats the problem.
The stock crank bolt on my car fail after like 90,000 mile allowing the balancer to moved forward,destroying a very expensive Black Magic Fan. Luck is with me that day since I was in heavy traffic at the time and was only doing 10-15 mph. It will be bad if I were at highway speed.........

Good luck in your search !

K.

The fan will definitely cause the motor to vibrate badly... Usually due to a crack in it. Mine almost broke completely off and then I went ahead and replaced it with an electric one and everything is all better

time only said:

Harmonic Balancer or Motor mounts ??

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Lost my HB last year. I was told that it's a "typical" problem. Mine separated, and destroyed the starter wire that is routed, imo, too close to it. Stock replacement is about $120 i think.

Yellowmustang52 said:

Lost my HB last year. I was told that it's a "typical" problem. Mine separated, and destroyed the starter wire that is routed, imo, too close to it. Stock replacement is about $120 i think.

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When I had the HB pulled out to replace the crank bolt,there was already a hair line crack on the snout of the stock HB,so I get to it just in time ( Now I had a SFI-18 spec HB and ARP crank bolt on the motor ). I was there when a friend in his 10 sec S/C Mustang had his HB comes apart in a hard launch couples of years back,luckly most of the pieces went down toward the track surface and not up into the hood or cut a tire.

89sportvert,Sorry for the thread hijack.

K.

John, if it is the fan, now's the time to go electric.