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View Full Version : The shake is gone



DickWells
05-08-2006, 19:12
When I test drove our 04 GMC DM CC LB out in Del Rio, I immediately noticed a little searching in the steering and a little shake or feeling of bounding down the road between 40 and 65mph. I told the salesman that the truck needed an allignment and balance, and that the problems needed to be fixed before I would trade. The next morning when I went back to test drive it again, the sailsman trotted out a service bulletin that delt with a problem with long-wheelbase GM trucks that shook up and down between 40 and 60mph. I think they called it frame shake or something. The cure? Put 200 to 500 lbs in the bed, behind the axle C/L.
I drove the truck again, and the wander was gone, (They lined it up) but the shake was still there. I traded anyway, and put my 250 lb box of tools behind the axle. The shake was all but elliminated.
Now jump ahead to yesterday. I put the 850 lb Bombardier Traxter that used to ride on the extended tongue of our old trailer into the back of the GMC, along with all the tools and other luggage. It must add up to around 1400-1500 lbs. No shake on launch, like before, and absolutely no shake between 40 - 60! The whole truck seems smoother and quieter. And, it rides better. Best of all, I can't feel any difference in the way it moves out. With the HyperTech set on level 3, this thing flat motivates! I know there has to be a difference because of the weight, but I'm hard-pressed to feel it.
MP, you were very right, when you told me here a week or so ago, that the universals had to be alligned to elliminate the shake. A half ton or so of extra load on there proves it. What a truck! If this thing keeps on keeping on the way it's been so far, you'll never get me to pry my cold, dead hands off the wheel. Now, if I could just find a way to make those seats more comfortable, I'd really be in full-timer heaven.
Dick Wells:)

More Power
05-08-2006, 22:17
Dick,

Launch shudder (when a truck has it) is generally most noticeable when moving out from a stop, and perhaps up to ~10-mph or so. The higher torque loads during a launch torques the rear axle (raises the pinion) and produces unequal u-joint angles (more than ~2-3 degrees difference between the two u-joints).

For some reason, bad (worn out & sloppy) u-joints are most noticeable at about 40-60 mph, depending on gearing and tire diameter (shaft speed).

Jim