Cabib Vibration

phattruk · May 25, 2011

chevy 2001 1500 hd 4x4, gibson exhaust, k&n intake, hid lights, plow package, tow package

i have a vibration that rattles the back window. This occurs only at 74 - 77 mph (yes i've paid precise attention to when it occurs). Above or below that speed and there is no vibration. i had a friend sit in the back and when this occured he pressed his hand against the rear cab wall below the window and the vibration stopped. I'm wondering if this is caused by the exhaust pipes, drive shaft or u-joints. The rear u-joints do squeak when in reverse and the truck will vibrate upon hard acceleration so i know they should be replaced. It is only the window that vibrates, the rest of the truck is smooth.

8.1HD/ALLISON · May 25, 2011

Sounds to me like you answered yourself. If you know you have a bad u joint, why wouldn't you start there? Replace it and recheck vibration.

Doug_Scott · May 25, 2011

Most likely a seized u-joint. For whatever reason driveshaft vibrations generally occur at multiples of 35mph. No idea why, just something I have noticed over the years. Started out when I was rebuilding Dodge auto transmissions (904 and 727, the real transmissions), if I did not put the drive shaft back in as it came out, it would vibrate at 35 to 40 mph. I would mark the shaft in relation to the diff. If I was out (it would be 180 degrees out) it would vibrate. Simply rotate the shaft 180 degrees and put it back in, vibration gone.

A seized u-joint would also give that low harmonic vibration, like a real low drone.

phattruk · May 25, 2011

Thanks. I will get the u-joint swapped out. This issue popped up before i noticed the U-joint complaining. i just thought it odd that it occurred at such a high rate of speed and no other speeds once i stopped accelerating.. . Plus since I have a dual drive shaft i may as well change the middle u-joint. does it make sense to get the axles balanced?

Doug_Scott · May 26, 2011

Thanks. I will get the u-joint swapped out. This issue popped up before i noticed the U-joint complaining. i just thought it odd that it occurred at such a high rate of speed and no other speeds once i stopped accelerating.. . Plus since I have a dual drive shaft i may as well change the middle u-joint. does it make sense to get the axles balanced?

You should not need to get them balanced, assuming they are not damaged in any way. Remember to mark the driveshafts before taking them apart. You need to keep them in phase with each other and with the parts they are connected to.

TRCM · May 26, 2011

Thanks. I will get the u-joint swapped out. This issue popped up before i noticed the U-joint complaining. i just thought it odd that it occurred at such a high rate of speed and no other speeds once i stopped accelerating.. . Plus since I have a dual drive shaft i may as well change the middle u-joint. does it make sense to get the axles balanced?

Axles balanced, no, driveshafts, yes. but unless you have really whacked them or knocked a weight off, they will be fine as long as they are still in phase.