What is this under my truck?

[PNW Raptor]

I was under my truck the other day installing some rebuilt shocks and noticed this weird rectangular block mounted in the space above my frame rail and beneath the bottom of the pickup bed. I have no clue what this is. Any ideas? It’s only on the drivers side.



Was at the dealer yesterday for a transmission flush and asked the techs there. Two of them had no clue either and one said he thought it was some kind of counterweight. It wobbles and has two rubber circular mounts in the middle.

 

[EricM]

Mass damper. NVH guys came up with that.

 

[PNW Raptor]

Ah, that makes sense. I figured it was some kind of balancer or something.

I assume it’s supposed to be loose like that to perform it’s function?

 

[Mick VT]

Ah, that makes sense. I figured it was some kind of balancer or something.

I assume it’s supposed to be loose like that to perform it’s function?

yes it is. Sometimes the rubber isolators wear out and it rattles. Without it you can get a bad resonant shake in the back end over rough ground