Vibration from bumps - shocks?

[r67northern]

Hi All,

I've been working through issues with the r20 and now I'm on to this one. There's a shake that happens when the truck hits a bump, if you're on the highway then it can set up a continual vibration that's annoying until hit hits a different road section and another bump kind of interrupts its rhythm for awhile.

But even at low speed you can kind of feel it if it hits a bump right in town. It's a small vibration that just goes undamped. The front end recently checked okay (at least that's what I was told). It drives tight.

Can shocks do something like this? I've got them on my list to replace, I usually expect shocks to damp the bigger motions in the road but should they be handling these small vibrations too? Maybe a body mount (or several)? Or could it even be something in the drivetrain that's shaking and needs some mount help?

Any thoughts appreciated as always.
Thanks,
-Leland

 

[skysurfer]

Put "death wobble" in the search box. Lots of causes, you just need to eliminate them one by one.

 

[r67northern]

Put "death wobble" in the search box. Lots of causes, you just need to eliminate them one by one.

Thanks, didn't realize this was a death wobble, I'll go digging.

 

[chengny]

A death wobble is hard to initiate at low speed and, if it is bad enough, it can almost tear the steering wheel out of your hands.

Shock absorbers were originally called dampers (and still are in most foreign vehicles). Once an up/down bounce is set into motion (by the springs) after going over a bump, the shock absorbers are designed to quickly dissipate the energy:


Springs deflect as the truck goes over a bump, then bounce back. The truck would continue to bounce up and down if the energy stored in the springs were not dissipated in some way.

The shock absorbers perform this function.

The primary function of the springs is to support the weight of the vehicle,

The primary function of the shocks is to absorb the "shock and rebound" of the vehicle (which is created by the action of the springs).

Without shocks, if you hit a good sized bump, you would continue to bounce up and down for a long time.

On the other hand, without springs, you wouldn't even be able to move - the truck would just slam down onto the axles and bottom out.

Shocks are easy to check. Jump up on the corners of the bumpers a few times until you get a good bounce going. Quickly jump off and watch - a good set of shocks will stop the bounce in one up/down cycle. If it keeps on bouncing, pull the shocks and try to collapse them by hand. If you can even come close to compressing the shocks required for a 3/4 ton truck...they are shot.

I'm not saying it can't be a DW - caused by front end/drive train/wheel/tire issues - but the shock bounce test is a good first diagnostic step. Cheap and easy.