If you lost one complete fan-blade (most are two pieces on the original fan) the vibration MIGHT not be there.
I lost 1/2 a fan blade on my 48... Noise was so loud I thought I had been shot by a 460 weatherby
..............
The entire truck was shaking like a 5 lb hammer had been left in a front tire...(thats another story,,,hehehe
). I pulled to the side of the road to look and expected to see pieces of engine missing and oil all over eveything when I lifted the hood. Not a sign of any trouble with the engine. I pulled the dipstick while the engine was running to look for metalflake/glitter in the iol but none. Had a real fun time trying to put the oil dipstick back in while the engine was shaking all over like a jackhammer, so I tosse it in the bed of the truck and got the rig home which was a mile and a half down the road. Thinking the rocker shaft or a pushrod had bent or broke, I pulled the valve cover to look. I reached down to grab the fanblade to roll the engine over and watch the rockers and pushrods move,,, my hand came up empty
..
Only three blades on my fan,,, Hmmm WTF
I looked up at the inside of the hood and not a scratch,,,, Looked down at the front crossmember and found a bent, twisted shiney object which use to be the fourth fanblade,,,,,, which luckily missed the brake line which crosses over to the right front brake,,,
I replaced the fan and engine ran great, no scared and shaking engine/entire truck
So ,, again, if you happened to lose both pieces of one entire blade, it MAY not have any vibration.
One more thought,, It COULD be possible for a hard object (such as a rock) to be
flung from a front tire, riccochet off the road surface and hit the underside of the hood or even the frame.
