I've noticed that when i get up between the 55-65 mph range the truck starts shake or vibrate ...especially the back. Its only in this speed range though. Any slower or any faster and its fine. My dad seems to think its the mud tires that make my ride quality horrible at that speed. My friends say when they're driving behind me at these speeds the rear axle moves alot. so is it the tires? transmission? shocks? sagging leaf springs? Im stumped...

 

how many miles are on your truck? it very well could be the tires

 

My bet is the tires are out of balance. Usually when a tire is OOB they have a certain range where they shake the most. This is because they hit a resonance. sounds like 55-65 is the resonance point. My old tires did this a while back. Just get them rebalanced and should be good to go.

 

How are your u-joints? They can cause vibrations at different speeds.

 

If your shaking in the back, I would say you have bad shocks. Bad shocks will cause your tires to lose contact with the road, and can also make your tires uneven. It
happened to me; if you looked at my tires they had high/low spots all the way around the tire tread, from the tire bouncing. Made for noisy shakey drive.

 

Forgot to say , if your tires are uneven /choppy you may need tires and shocks to smooth the ride. If there not that bad the new shocks may cause them to wear flat after a while again.

 

Out of balance tires, if you bought them from a store or what not, take them back and ask them if you can get them re-balanced.
easiest way to check to see if its a bad u-joint is to throw the truck in Neutral while driving along and if the vibration changes or goes away, its driveline.

 

Wirelessly posted (iPhone 3GS)

Also the tires may be out if round. The way to determine this is with a road force balancer. It will measure the roundness of the tire. Anything over 15 I think will give a shake. Like full scale said check universal joints. Inspect wheels for any bends.

 

143,000

 

so it sounds like I should go get my tires re-balanced and if that doesnt fix it get new shocks...

 

Balance and rotate. You can check yor shocks by pushing on the bumpers to get the truck moving up and down. Truck should stop moving up and down right away when yoy let go. If it stil bounces up and down , your shocks are bad.

 

Is it this bad? HAHA

 

haha no its not that bad. its just a little shaky not the whole rear end getting airborn.

 

I got my spindles put on today and they did an alignment, balanced and rotated tires. I havent gotten a chance to check if the problem is gone yet though

 

I checked the shocks tonight using your method...the problem is definitely not the shocks. After the alignment It rides lil smoother but I think its tires being outta balance. Im getting 35s soon so should I wait til then or just get them balanced now?