High speed shimmy from bumps

Hello! First post and first time taco driver.

2003, 6 cyl, 4wd, 5 speed, 6 foot bed and access (?) cab. Stock suspension. IIRC 265/70 R16 AT tires, almost new, balanced.

At highway speeds when I hit bumps, the back end of the truck shimmies (side to side). I've had the thing going a little sideways entering icy overpasses because of this.

Any ideas on why this is happening?

Thanks in advance!

 

Shocks?

 

Shocks and/or leafs? Mine used to do that and I replaced both, handles great now. Well, for a truck.

 

Leafs in the back. Rear shocks look older than the front... Don't know brand of anything.

 

Are they yellow with blue boots? How many miles on your truck?

 

Black with the leafs. Gray in the front.

 

170K

 

If the rear shocks aren't damping the rear suspension oscillations correctly, it will cause the back end to "step out" like you're describing.
You can remove one or both of the shocks from the truck and test their compression/rebound by putting one end on the ground and pushing on the other end. If they feel soft, spongy, or have very little resistance, they're probably blown and need to be replaced.

 

I have a similar issue on my 2003 4 door short bed, but my shocks and struts were replaced 30k miles ago. When i got new tires it helped but it still does it. Rear shocks are pretty cheap and easy to change out so it may be worth a try

 

So I just noticed the rear passenger side is sitting about an inch lower than the driver side. It must have just started doing this. Looks like I'll be replacing some suspension asap...

Might put in some of those air bag kits for the heavier loads I've been running.

 

That'd do it, heavy load and blown shocks will send you bouncing left and right

 

Try replacing shocks first,give it a drive and if need be replace the springs and add some load cushions.

 

Put some weight on the back to improve how smooth it rides back there. Even with new springs and shocks you won't have a smooth ride unloaded unless you go with super light springs that would sag a lot with any weight in the bed. It's just part of owning a vehicle made to support a varied load in back. Sounds like you could use some new components out back though.

 

Thanks for the responses everyone.

I'm thinking about some KYB monomax or Bilstein heavy duty shocks (something in that price range).

Do any of you have experience with airbags? While I don't do a lot of serious off-road, I do live in the mountains. The main usage of my truck is moving around gear, so instead of installing super beefy springs (that will ride like shit on and off road) I was just going to slap in some air bags and adjust the pressure as needed.