Vivbration/shudder while decelerating with very light throttle

[estoguy]

Hey guys and gals,,

Having this odd vibration/shudder that is in the rear when decelerating. Feels like the whole back end is shaking around, but it's only happening when there is very light throttle input (my foot is just barely putting pressure on it... maybe a few millimeters or if I'm going downhill with the cruise and it lets off on the throttle). If I take my foot right off or add more throttle, it immediately goes away. I'm mainly noticing this at highway speeds above 80 km/h.

There is no clunking or issues when shifting gears or accelerating - everything seems smooth enough. I recently had some new tires mounted to the back rims and they were balanced. I did notice today, that the left rear didn't have an outer weight, but as stated, not getting any vibration any other time that might suggest an out of balance tire. Rear shock mounts were replaced last fall. Rear shocks and links seem OK.

Thoughts? I was leaning towards transmission or engine mounts, but lack of issues I've been reading about have me a little stumped.

As always, thanks for the input!

[TobyB]

The unloaded condiion makes me think driveshaft-
if the guibo & csb are good, maybe take it out
and check the u- joints for binding and the little
pilot nipple at the trans...

t

[redsubdivisions]

I had this issue and it is definitely driveline related. Turned out my guibo/flex disc bolts were loose and one sheared off! I'm lucky my guibo didn't shred to pieces. Got some OEM ones from the dealer and all is right again. Might as well check your CSB too.

[jeffnhiscars]

I'm thinking u joints as well but if the problem started when you got the new tires before I dug too deep id switch the rear tires from side to side. That solved a similar problem for me on the front end....seems it's not all that infrequent for belts to shift in the mold making some tires happier spinning in one direction than the other.