Front-to-rear bounce at 45 MPH in 2002 Duramax Diesel Shortbed

I have a 2002, short bed, quad cab that I purchased used (70,000 miles). When I reach about 45 MPH, it does a front-to-rear bounce which goes away at 50 MPH. It did this while I test drove the truck. The truck is all stock (no lift kit or anything else). I had the sales person look into it, so he sent it to a local tire store. Their answer was “worn tires and front end alignment.” So, I bought the truck. The shocks have been replaced, tires are new, front end aligned. It’s still there! I did hear a rumor that this is a problem inherent with the short bed, quad cabs. True or false? What can I do, since it is somewhat annoying especially when you have passengers. Thanks.

What you are experiencing is known as chassis beaming. That is a term that the engineers use to describe the frame of the truck bouncing and flexing like a spring. Every automobile manufactured allows a certain amount of flex or deflection in the chassis, including the best sport cars. Generally, manufacturers spend considerable time making modern car and truck chassis more rigid. Making chassis stiffer has a host of advantages, with improved stability and handling being the primary ones. It can also reduce the potential for rattles and noises from the deflection of body or interior parts going down the road.

When the engineers were drafting up the design considerations for the GMT-800 (1999-2007) trucks they wanted to make the chassis considerably stiffer than the prior generation of GM trucks (GMT-400). This was accomplished by using advanced manufacturing techniques like hydroforming as well as tried methods such a box sectioned areas. As a result, the GMT-800 frame is far more rigid than the previous designs, with all of the advantages mentioned above. So why do these trucks have a tendency for the chassis to beam, or bounce, at certain speeds?

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Joel Paynton is an award-winning GM technician who specializes in Duramax fuel systems. He also does custom programming for any GM powertrain. Visit him on the web at


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