ok this just started after installing bmr suspension tube lower control arms with poly bushings.
cruising at highway speeds (65 mph) the rear end starts vibrating but its like a pulse and gets worse and more consistent at higher speeds.. its an 82 z28 with the stock rear end as far as i know.
any ideas on what it could be? its making me quite uncomfortable esp. when my son is riding with me. i retightened the lower control arms last week and it helped a little now its starting to get worse.

 

well i figured i would start with seeing if the tires were out of balance so i had them rebalanced and it helped just a little. the axle shafts have a little bit of play in them. any one have any ideas?

 

Check your u- joints for play, especially the front....

 

i had replaced them about 4 months ago. i disconnected the driveshaft and spun the tire as fast as i could get it and it made the grinding sound from inside the differential. i think its the pinion bearing

 

bummer....

 

yea especially since its really my only vehicle.. i can ride my motorcycle except for when wind gusts are at about 20mph.

 

its the motor mounts... they have excessive play