5.3LGMC

Hey...when i get her to about 25mph or so and punch it she drops down in a gear and just plain SCREEMS....then shifts...during both of these the truck sort of has a vibration to it somewhere...if anyone has had a quad or dirtbike clutch go on them this is what that feels like...i recently got new winter tires and the drivers side back wheel balance weight has fallen off? could this be causing this vibration at high rpm under acceleration? The truck doesnt vibrate at crusing speeds and i can put her in neutral at 70mph or so and rev it up to about 5 thousand rpms and its smooth.??? any ideas... Its only when it really screems high on the rpms that i feel it.

phatboy

your pinion angle is changing when you mash it. do you have drop shackles? if so then you need to correct the pinion angle with some wedges.

5.3LGMC

It never did nothing like this before and no the truck isnt dropped...it just seemed to sstart doing it around the time of the tires? Guess ill get it balanced again and see whats happening then......ACTUALLY could a couple hundred or a hundred extra pounds in the very back of the box cause this? ccause i do have sand bags in there for winter...thats the onlythings that have changed since before....

Mort

May as well check your u-joints while you are getting that tire balanced. Yes a load in the bed will lower the truck some but the drive line angle changes will not be as extreme as a drop and will not normally cause any problems. Maybe doing WOT down shifts with the weight in the bed is causing the problem. Easy to tell, just take the weight out and see if the problem goes away.

Eliminate the wheel balance and weight in the box problems first and then go from there. Try to change one variable at a time until you figure out what is causing the vibration.

Good luck.