I'm pickin up BAD vibrations - Ford F150 Forum

Just a good ol' boy · 10-25-2009, 03:46 PM

I have a 79' F-250 4x4 with a 400 ci and 4 speed tranny. Recently, I have noticed the truck is vibrating at higher speeds. Usually anytime I get near 50 mph the truck will begin to get louder and vibrate, shaking the entire truck. The shake is not a violent shake, but it is noticeable. I had an alignment done and the tires balanced, but it didn't seem to help much. Also, when I let off the gas, anytime I am driving faster than 50 mph, the truck does not seem to want to idle down. It makes a loud noise almost as if I had downshifted (but I simply let off of the gas.) Any thoughts would be greatly appreciated! Thanks.

okie · 10-25-2009, 06:56 PM

Don't know the condition of your tires, but if you have a good spare, you can eliminate a tire problem by putting your spare on each corner at a time and driving it. Next I would check u-joints & front steering parts.

okie

tsumrall · 10-27-2009, 06:59 PM

Sounds like tires but...
Check your drive shaft. Ujoints should have zero play. Lube while your there

The shaft has balance weights, make sure one was not lost.

tsumrall · 10-27-2009, 07:03 PM

On idle down problem. Not sure why just at over 50 mpg but
Check your trottle linkage at the carb. A little spray lube won't hurt.
Check your trottle return springs. They could be missing or weak.

Is it truely downshifting? or just sound like it?

D&CBrown · 11-02-2009, 08:29 PM

If you have a carrier bearing you might check it.

ecoguard · 11-19-2009, 10:34 AM

i had the same prob with my f100, the u joints had come apart. better fix it quick, can make a real mess