the on and off wobble

[antnykk]

My FSB is driving me crazy.
I have a high-speed vibration/shake that starts around 65mph and on. The weird thing is that is comes and goes every 5-10 secs.

You can sit at 70mph and not change a thing (direction, rpm, road speed, etc.) and the vibration will come and go every 5 secs or so. 5 sec on, 5 sec off.
The vibration is felt through the whole truck (seat not wheel).
It is dependent on road speed and not engine speed or gear selection (auto E4OD).
Geeting on the throttle or off does not change anything.

tommorow I am going to start to check joints, but why would the shake keep smoothing out by itself if a joint was bad??????

 

[reynard101]

All vibration frequencies vary with time, some are very short (milliseconds) and feel like a constant vibration, others like your case, oscillate between longer times. Generally speaking, the longer between constant vibrations, the heavier the object that is creating the vibration. Heavier objects have lower natural frequencies.

I would look to see if a tire is out of balance or possibly a tire seperation. Tire seperations are sometimes a bubble on the tire or more subtle like a small irregularity in the tread or sidewall.

 

[Eoth]

I have found that two slightly out of balance tires that by themselves were not bad enough to cause a vibration (or countered each other out). But when their rotation matched each other their combined effect caused the vibration. This will happen due to the different distances that the inside and outside tires travel around turns. Of course none of this applies if the road is perfectly straight and you still have the vibration coming and going... If that is the case go get your tires rebalanced.

 

[cootvon]

tires....

just went through the same thing. finally got it right after 8oz of airsoft beads
in each tire... thanks to the folks here

 

[antnykk]

Just ordered tires and will be putting them on Tuesday. I will let you know what happens. Thanks for the replies.

 

[BG's 68 Bronco]

make sure the inside of the rim doesn't have mud caked on it either... that will give the same symptoms.