I live out here in Sunny Arizona, and one of the major highways I drive on frequently makes for an interesting ride. The expansion joints or some other imperfections in the road surface cause my truck to oscillate front to back quite significantly (a few times/second). It is significant enough and fast enough that you can actually here the effects on someone's voice as they talk. This happens at speeds around 65 to 70 MPH. It doesn't do this on other highways so it is not a balance problem. Speeding up or slowing down will temporarily stop it, but the speed of the traffic flow is the speed that causes this to occur. Is there anything out there that would dampen this?

 

[updated:LAST EDITED ON 13-Dec-02 AT 03:19 PM (EST)]More than likely shocks !
But you haven't given us much detail on your truck
what yr ,model ,4x4 ?
any mods?

Rich

on edit I noticed your name !
bilstiens and rancho's are shocks of choice around here!


02 F250 4x4 SC 5.4v8 6spd 3.73ls Trueblue/Silver and Chrome Nerfs

"All Levers"

 

Like Forty said we need more detailed info on your rig. But if your truck is "bucking" front to back. That sounds like the dampening process on your shocks has left the building. If it's a SD then the truck going ape shat after hitting a rough expansion joint is kinda normal when it's stock due to the way it's set up from Ford. But it shouldn't continue down the road.

 

The truck is a 2000 F250 Superduty, extended cab, long bed. It is a 4X4, stock height, but I've added 285X70X16's. It has 32K miles. I've never noticed the shocks taking a while to settle down on pot holes or rough roads, but at 32K miles maybe they are getting close. What's the recomendation if it is the shocks?

 

I know what you are talking about. Last spring there was a stretch of Interstate 55 (now resurfaced) between Blythville and Osceola in Arkansas that gave the impression you were riding a bucking bronc. At certain speeds, harmonic frequencies were developed that would almost bump your head on the roof. The suspension seemed to pound at every expansion strip. Everything on the truck was new at that time so I didn't blame the equipment just the Arkansas Hwy Dept. People that lived in that area, driving softer sprung vehicles, didn't seem to notice.
Fortunately I was only on vacation and didn't have to drive that stretch like you do in Arizona each day.
I have the long wheelbase like you and wonder if that might be a factor?


2002, SC, F250, V10, Long Bed

 

I have had the same problem, on two 02 PSD 4X4's. Worst on cement Interstate highways with an expansion joint about every 1.5 to 2.0 truck lengths. Singular pot holes and irregularities the truck just seems to soak up smoothly, even with stock shocks. This truck rides as good as my 92 Caddy, until you get on certain sections of interstate. IMO, this is what is happening. The front end impacts the expansion crevice the springs compress and roll through. Before the front springs and shocks can fully recover the rear hits the previous crevice creating another impact. The secondary impact creats a force vector that is in oppopsition to the recovery vector of the first. This cycle is repeated due to the distance positioning of the impact points. Each impact vector exacerbates the amplitude of the other, a cycle. Impacts of this type and force will additionlly cause other undamped parts to resonate at their natural frequency. A time wawe form of this impacting interaction would look like two sine waves with peaks not 180 out just slightly off peak relative to the other. What does all that gobledy gook vibration speak mean? Get better shocks that are capable of changing the damping rate / recovery of the system. I have been meaning to do it, but I have been out of town away for a couple of months. I want to attach an accelerometer and real time vibration analyzer(vertical on axis and perpendicular to the axis) before I change the stock shocks out. Take data on particularly nasty 5 miles of road, peak hold spectra, record for a base line. Change the stock shocks out install Rancho 9000's and take comparison spectra, same place distance and road speed. Definitive data I will share. Got to order the shocks today, about a $300 experiment, my wife just shakes her head, with a when will he grow up look, when I do stuff like this.

Regards, James-David

 

I think you nailed it on the head. The spacing of the joints on this particular highway are just "right" for the size of my truck. I just wonder if Rancho 9000's can dampen it.