Throbbing under driver's floor
 

1999 F350, IH V-8 Turbo Diesel, 6 speed RWD.
At about 65 to 70 I was feeling a intermittent vibration right under the driver's floor. It is not a 1 to1 wheel vibration or an out of balance sensation.
I put the truck on the lift and checked the wheel bearings and ball joints. Both sides are solid, no wiggling or looseness.
I did examine all the "rubber" bushings and found the sway bar end bushings and the bushings that go to the short arms are dry, cracked and probably original.
I'll be changing all of them for good measure.
One thing did catch my eye was some "rust dust" of fretting evidence on the bushing for the I beam near the middle of the truck.
I am guessing these bushings are original and changing them, especially given the "rust dust", would be a good idea.

I'd appreciate any thoughts on this and if there is any guidance on removing the I beam and the two fore arms I'd like to hear it.

Thank you!
Best wishes,
Eric

Hi Eric,
Did you do any work on the driveline/driveshaft?
Sounds like something may be out of phase.

Hi Hanky!
No I didn't do anything to the drive line or shaft at all. I did check the u joints and there was no play.
I looked at the center support bearing and found that the rubber was still flexible but I have no comparison to see if that is normal or within "tolerance".

The vibration is not constant. It comes and goes randomly.
Eric

Are there any visable rust trails around any of the U-Joints?

No rust trails or dust any where on the drive line, U joints but only on one bolt on the right side I beam center attaching point. That particular spot is in he vicinity of where I feel the throbbing in the floor board. Wondering if some sort of intermittent sympathetic vibration is causing a resonance to be felt.
The bushings all seem to be original (1999) but I really don't know how to determine if they are shot. The rust dust at that mounting point is the only thing that caught my eye.

You ready for the cold? 20F here now in Bowling Green KY.
Regards,
Eric

Hi Eric, Merry Christmas to you and and all Ford family on this forum.
It's 10:30 AM here now and 21 F, so I have some Idea what you are talking about.

As you know any rust trails are something we should look into further, but not sure where you are seeing this.
Can you help us out here, thanks.

ON the front suspension there are four arms, Two that are aligned front to rear and two left to right,
The left to right arms (I beams I think is the term) have a pivot point at about the middle of the truck. The mounting bracket for the right arm pivot point has a rust dust trail on one of the mounting bolts. I suspect this rust is coming from inside the bushing or bushing housing.
I am considering changing the bushings for al four arms as they seem to be original (1999).

And one added item. When driving yesterday at 70 MPH cruise control on 6th gear I heard and felt the throbbing. I shifted into neutral and let the truck coast and the noise & throbbing stopped.
This leads me to think that the center carrier/support bearing is in fact shot. I have ordered a new high quality unit.(Dana brand) I now need to fabricate a puller for it. A job easily handled in Hoffmeyer's Machine Shop.


THoughts/commenst?
Merry Christmas.
Eric

If you really have a Machine Shop, you at least don't have to pay for the labor, we hope ! lol

When you can, there are a lot of folks here that could benefit from your experience and we all would appreciate your assistance when possible , thanks.

Nice post Hanky!

I agree - it would be great to have access to opinions from someone with significant machine shop experience and expertise!

It is really nice to hear from the members of our Ford Family.
Wishing all a Merry Christmas and A Happy , Healthy New Year.