On a long trip, after I have been on the highway for about 4-5 hours, the rear of the truck jumps up and down quite violently.<br>It actually woke my wife up from a nap on our last trip.<br>I put 4 tires on the truck and was towing the S-10 the following weekend to Lake George.<br>Same thing but not as violent, maybe because of having the trailer.<br>I was thinking that maybe it was something in the rear end.<br>Have also changed all u-joints, haven't tried it yet, <br>Any ideas ??

 

Does it happen at a certain speed or rpm...does it get worst the faster you go ??

 

On the trip to PA it happened at about 55mph and above<br>On the return trip, it was raining too hard to go above 60 for any sustained time<br><br>On the trip to lake george, it happened about the same speed<br>On the return trip, it only did it once, but we were in traffic most of the time. <br> <br>I was thinking of changing rear diff fluid to synthetic w/additive<br>The truck has 4:10 LSD, 285/75/16 tires with Equal in all four now, but have not been on a long enough trip to feel the hop.

 

Richard<br>At that speed it could be a out of balanced tire or a out of round tire<br>My first guess would be a out of round tire that gets worst with a load (trailer) causing it to bounce<br>Both of these can be checked by any tire store

 

I put the adjustable Rancho shocks all around on my truck. The result on the stiffer position of 4 or 5 easily results in a heck of a bouncy ride over 50 mph. My wife would call it quite violent. Every tiny bump was magnified. Is it possible that your shocks are too aggressive or maybe if you have Airbags...is their air pressure to high? <br>Just my .02 cents... [undecided]<br><br><br>TJ