i have a 97 f150 with a 4.6 engine. i have developed a problem somewhere on this truck. it acts like the belts have let go on the rear tires. going over a long bridge that goes up and over a large body of water you can feel the back of the truck sort of wabble at low and somewhat faster speeds. i have put all new tires on the truck. it still does it. i have had a ford dealer check out the rear end, they say it is fine. i had the tires rebalanced but the problem still exits. i do have the original shocks on it. ford dealer also checked out the suspension , say its ok too. this wabble, bouncing is very noticable. has anyone out there experienced this problem? can you give me any advice as what to check or do.

 

All 1997 thru 2003 F150's I have owned has had some issue with "highway hop" The rear suspension along with frame resonance can put you in a wave at certain speeds and road conditions. There was mass-damper add to the rear of the frame at one point but not sure if it is still an open TSB with Ford or not.

Try this: Get a sand bag or Two (30 -40lbs) and place them in your bed in either right or left rear quarter. You may have to move them a round a bit to find the correct spot. This may help but a mass-damper isolated by rubber bushings attached to the frame would be a more permanent fix.

Note: I have had 4 PN96 trucks. 1) 97 4x2 Super cab. 2) 01 4x4 SuperCrew 3) 03) 4x4 SuperCrew Now back to an 01 4x4 Supercab. All of them resonated in the same stretch of road in Wayne MI. on may way into work. I just pick a different lane and live with it.

2004 + MY vehicles have all new frames and should be OK.

 

If you have the orginal shocks on a 97, they were worn out long ago. They may not be th problem, but they can't be helping it.

 

Yep, never hurts to replace old crappy shocks.

 

Yep, and throw some Bilstein's on there while you're at it.