i posted a thread a few weeks back and got lots of replies, thanks. but my truck is still vibrating. i had it balanced for the 4th time today and it is 10 times better but still shakes. i can still slightly feel it at all speeds and under all gears and throttle inputs, but now its magic harmonic super shake does it at 60-70 mph while accelerating. nuetral or clutch in and its smooth.

this was not the case the other 3 times i had it balanced down in florida, it would react differently each time. i suspect something else can still be wrong with my truck, but i am sick and tired of shooting from the hip and just throwing money at it and "hoping" to fix the problem. this goes against my beliefs and how i was taught to troubleshoot.

what caused all the madness in the first place when i had a perfectly fine truck? removal and inspection of the drivetrain by myself, failure to index, and re-installation of the two halves THE WRONG WAY, then ofcourse driving it that way for 100 miles, then putting it back the right way, and driving it for 1000 miles. then deciding to get it balanced 4 times.

wheels have been rotated properly. new ujoints. new carrier bearing. trans mount is tight. tailshaft has tiny play in it.

 

I think you are throwing good money at a bad driveshaft. If it were my truck Id just buy a used driveshaft from a boneyard. That way you know for sure whether the problem lies in the shaft. I dont know the prices around your area but I can pick up one from the junkyard for $25-$40 depending on length and amount of joints.

 

john thanks for the help, i do understand its a stick of metal that is subject to many different stresses that has a multitude of problems with it, but i just couldnt see why it is not fixable. 2 different shops now have worked on this shaft, the first did it 3 times. i do not see how you cant take any shaft to them and have it run perfectly smooth afterwards. i thought about just going with a custom aluminum racing shaft from dennys driveshafts in upstate new york. the boneyard sounds like a good idea as well, but then i would have an old carrier bearing, and old ujoints, which i dont want, because then when those seize up, the shaft will dance around, and now i'll have more problems.

 

Have you checked your suspension components?

 

My suggestion to buy a used shaft is to narrow down your problem. If it still vibrates then you know it isnt the problem. If it fixes it, then you can purchase new joints and bearing to go with the used shaft. Regardless, its gonna be way cheaper than a custom shaft.

 

When the truck is in motion, the rear driveshaft spins even when the clutch is "in" and/or the tranny is in neutral. Yet you say things are "smooth" when the drive-line is disengaged . Which would seem to indicate that it's not a driveshaft issue.

 

I still believe that it is a driveshaft problem. Especially since everytime he has the shaft worked on it "feels" different and vibrates less. If there was nothing wrong with the shaft there would be no room for improvement. There very easily could be other problems as well but the major issue is the driveshaft.

The harmonic shake that lessens when the load is removed can easily still be driveshaft related. When under load, the suspension moves slightly which will change differential height, pinion angle, cause the rear shaft to slide further into the slip yoke, and cause the carrier bearing to flex. These conditions will further contribute to driveline vibration when the driveshaft is distorted or out of balance.

Unless you bent the tailshaft in the transmission or pinion in the differential when you incorrectly installed the shaft theres really not anything else that will cause what you describe.

 

you hit it right on the nose