Merica' Made

04 Chevy avalanche 5.3 2WD

recently purchased used vehicle, engine runs great, with 170k miles.

During slightly heavy acceleration it starts to vibrate fairly strong. seems to be coming from the engine and/or the center of the truck. in park or placed in neutral and revving the engine there's 0 vibration, not even with slow take off or slight acceleration while in movement. I suspect u-joint as that seems to be the pretty common issue but can't find any slack or play in it when I try to shake it or move it around. about to try a new set of plugs in it but still looking for suggestions..

Irish_alley

since its based off the load you can assume its anywhere from the trans back including the trans itself. u-Joints would prob be the cheapest does it have a two piece shaft? if so the carrier bearing can do the same thing and i would suspect that over u-joints

mountainmanjoe

Lift the back wheels off the ground. Put it in gear, and have a buddy apply some throttle and a bit of brake at the same time. Try reverse too. Then you you can get a closer look and maybe prod around with a mechanic's stethoscope. Just be careful and secure the vehicle really well.

Merica' Made

Although I seriously doubt I can't help but ask the opinion of y'alls experience. I noticed both of my front lower bump stocks were completely deteriorated so I made a makeshift bump stop on each side score up 100 mile trip that I had and it literally made this truck ride with almost zero vibration... Of course that can be a cause of some vibration but to think that my front suspension and shocks / struts along with absorbers and stops what to give me such a harsh vibration only under load
.. opinions?

mountainmanjoe

No. Deteriorated bump stops do not cause vibration.

Irish_alley

vibrations have to come from something having rotational energy (fan, dirveshaft, engine, trans, axles, axles shafts, tires/wheels and maybe a few other things). shocks, struts and bump stops will not cause vibrations (maybe a clunk or bouncing). if you took a tire off you could of tightened the wheel down differently and that itself could of been an issue

Merica' Made

Thinking it's a culmination of issues from the front end suspension and tires; which most likely caused drive shaft imbalance, uneven motor mount wear or even further going down to the torque converter and possible transmission... Busted lower tie rods along with all bushings, ball joints and pretty much damn near everything on the front suspension being worn the hell outI'm going to just take it piece by piece on that front end...
Definitely agree that shocks/struts/bump stops wouldn't cause much vibration, especially that harsh when its under load only, if any at all, but it blows my mind that just a replacement of both bump stops has reduced it by roughly 80%... Now it's a slight vibration under load for 3 to 6 seconds Max and then a steady vibration at 70 + mph

Merica' Made

FIXED Vibration Issue

Found the cause to be the Rear U-joint on the Driveshaft. The connecting pin was offset about 1/4" with one of the coupler clamps loose, that has two mounting nuts, barely attached. Just greased the U-joint connecting pin and hammered it back in place and then secured the coupler clamp by driving the nut all the way in and torquing by hand. IMMEDIATELY fixed the Vibration Issue, rides smooth and straight!!