Beam Shake

[Greg]

I tend to notice more harmonic motion on concrete roads with an extended cab truck than any others. But, nothing like this. Have any of you experienced this?

 

http://www.lsj.com/apps/pbcs.dll/article?A...80338/1016/news

[Larry]

Greg,

 

This is a very common occurrence on all full size trucks….period. Although, most noticeable on extended cab and crew cab trucks….especially on short bed trucks where the frame rail under the cab are actually longer than the frame rails under the bed. As the vehicle suspension moves up and down the frame start to resonate and flex in the middle below the cab, as it should. If the frame did not flex it would crack. The resonation frequency is usually around 10 to 25 Hz when really sounding off after being initiated by constant driving on expansion joints, etc. This gives the “bounce” feeling.

 

Most people do not even notice or comment on this “beam shake” as they realize they are driving a TRUCK.

 

The GMT 800 trucks are less likely to have a noticeable “beam shake” due to the rigid hydro-formed frame. The older GMT 400 trucks had much more pronounced frame resonance. If you want to drive something with major beam shake drive a spaghetti frame 1997 through 2003 F150 extended cab short bed. Then you will really feel “beam shake” first hand.

 

I cannot believe this situation made into a newspaper in Lansing. It would be easy to poke fun at the owner of the truck in the Lansing article and call him a soft palm flit boy (which he maybe) but he had a concern and brought it to his dealers attention. Nothing wrong with that. For the purpose of customer satisfaction the dealer made some adjustments, tire rotation, wheel balance, etc. Nothing wrong with that either.

 

From that point on is where the dealer dropped the ball (replacing who knows what… the article says “whole new drivetrain”) and turned a normal characteristic into a big issue for this customer while wasting warranty dollars in the mean time. Very hard to tell a customer his concern is a Normal Characteristic only after the dealer has had the truck out of service for days and thrown countless parts at it.

 

The service manager stated he had never heard of “Beam Shake” until he read the bulletin. Well, either he is new to the truck world, lives under a rock, lying to cover for his warranty expense, or just an idiot. And why is he not reading bulletins as they are published anyway?? Reading newly published bulletins are a responsiblity of the Service Manager or Shopforeman then they pass it on to the techs at meetings and such. Did he or his technician contact GM TAC for guidance? Probably not.

 

OK, so beam shake is normal…what to do to lesson it if it really bothers somebody??

 

1. Reduce tire air pressure (scary in the post-Firestone/Explorer world)

2. Place 200 – 300 lbs of sand bags at the very rear of the truck to stabilize the rear of the frame

3. Add a camper shell, topper or something that will add weight on the rear portion of the frame.

4. By a car