raw21

hello,
i have a 97 f150 that has been giving me some shimming or vibration
only when i am driving at speeds between 42-45 mph and when i
am braking and slowing down only when i hit this same speed i feel it too.
i had all my wheels balanced twice at two different garages, i also
went around all four wheels and put my spare on and drove it one at a time and still did the same so i pretty sure its not a tire. looked at the main drive shaft and it looks okay no weights missing from what i can tell.
did anyone ever have this problem? or have any suggestions?
thanks, raw21

rally

I had a similar problem in my 1981 F100, where there was a vibration at about 25, 55 and 110km/h. It was obviously a harmonic problem somewhere, but I was never able to trace it. Did everything you did and also had the tailshaft balanced several times.....

Dellboy999

Engine out of balance, if you get up to the speed, then put the engine in neutral to reduce revs, does it still feel the same or smooth, hamonic balancer at the front of the engine might be out if it is the case. In neutral can you get the same revs up and it does it or only when driving.

Dellboy999

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raw21

i will try what you said about shifting to neutral
today after work and let you know what happens thanks
for the replies

raw21

well i did the shift into neutral and the rpm's went down, as i coasted to the 42 mph it did still shimmy, and also when i hit the brakes at this same speed. so what does that tell me now?