Hi All,

My 92 4X4 reg. cab pickup (manual 5-speed) has a annoying "bounce" between 38-45mph. Tires are new and have been rotated - nothing changes.
Truck has 64k miles on it and is riding on its original shocks. The bounce is felt in the seat of my pants. No vibration in the steering wheel and no front
end bounce. no clunking in the drive line. Sometimes it barely noticeable, others very noticeable. If I depress the clutch and coast, or shift into neutral and
coast, there is no bounce in that speed range or anywhere else. I can feel it accelerating up through that speed reange in 4th or 5th gear. Adding weight to
the gack doesn't seem to make any difference. The bounce isn't a floating sensation like worn shocks, but rather short and abrupt like super heavy duty shocks.
the up down motion (rate) does not seem to increase or descrease with speed. If anyone has experienced this and solved it, I sure would like to know.

Thanks
Tonino
P.S. In case anyone missed my previous dilemma (squaky clutch pedal), I solved that be replacing a 25 year old pushrod between the clutch pedal and
clutch master cylinder. The pushrod has a steel encased rubber bushing on the pedal end that dries out, shrinks and cracks. The bushing squishes
around in its casing and makes that weird screeching noise. A new pushrod will solve it.

 

I had all the same symptoms, i replaced everything,the yokes and center bushing on the driveshaft reduced the vibration a lot, but the final solution was the rear wheel bearing. check the rear shoes, if they have an uneven wear on them its likely that side vibrating and rubbing. lifting the rear end up with jackstands and having a friend get it to speed is also a way to see what's up under there. good luck

 

Did the bounce start before or after the new tires? I would replace the shocks, not necessarily as a fix but 64k is about enough.

 

Thank you for the reply. Shocks are on my list, It was there when I bought the truck and the new tires
didn't make any difference. Rotating them from back to front didn't change anything either. It feels
like a rear shoe is touching an out of round brake drum but why only in that speed range? I'll pulll
the drums and see whats what back there. Thanks. 64k Miles' and 26 years is WAY long enough for shocks.

 

Given this I wouldn't be surprised if it is the shocks. They aren't working and at around 38-45 mph you may just be hitting the harmonic of the springs and . . . bouncing vs the shocks dampening the harmonic.