small oscillating driveline vibration from 70-90mph

[lukem80]

after every thing on the car is warmed up good.. going down the interstate at 70-90 the car will have an oscillating drive line vibration that comes and goes. I feel it in my ass. not the steering wheel. feels like a drive shaft out of balance to me or the drive line angle is wrong.

what do you think?

bad motor/trans mounts

out of balance drive shaft/half shafts

bad u joint(s)?

car has 15,000 miles on it. 2000 GTS

the tires are brand new Nittos. I had some Proxies on it before and it did the same thing so I'm guessing its not tires.

I am going to get an alignment done this week to eliminate if that is causing some of the problem. (very doubtful)

I also have a slight whine in 5th/6th gear above 60mph. I can't tell if its in the rear end or transmission. it only happens under load. the drive line vibration only happens under load also. if you coast its smooth with no whine.

I changed the transmission fluid and diff fluid last month with no change in vibration and sounds.

I'm not so much worried about the whine if its the transmission, but if its the diff I need to probably address it.

I'm just looking for opinions before I start to throw money at parts.

I know the motor/trans mounts are garbage on these cars so I'll probably replace them anyways.

thanks!

 

[mjorgensen Woodhouse]

Bad shock?

 

[lukem80]

interesting idea. i'll check that out also. how can I check if it has bad motor mounts/trans mounts. hand brake on. let clutch out with hood up and see if the driver's side moves up too high?

 

[mjorgensen Woodhouse]

interesting idea. i'll check that out also. how can I check if it has bad motor mounts/trans mounts. hand brake on. let clutch out with hood up and see if the driver's side moves up too high?

You basically have to try and jack up the engine a little to see if mounts are separated or really squashed down, same with the trans mount.

 

[lukem80]

the whining noise is coming from the transmission.

I don't know about the high speed vibration though.