I'm having a really strong vibration starting at 70mph. The steering wheel is not shaking, so i'm guessing its in the back, I just had all my wheels balanced, no waits came up missing recently so i'm guessing it's not the wheels.
Also, if i make left turns above 50mph it feels like my rear end "hops", i can feel how it just slips away. Only left turns, and only at moderate speed. At lower speeds i can't notice it at all.
It also seems like it's less noticable with a full tank of gas.
HELP!!! i almost lost it on the interstate today, changing lanes.
what could it be?

 

Does the vibration go away under decel?

 

no.

 

Have you checked to make sure nothing is broken in the suspension? And why did you just have your wheels balanced? Did this start soon after you installed new tires?

 

Buy new tires. I had something similar and it was my rear tires telling me they had nothing left. I didn't even realize that the inner part of the tread was almost down to the cords due to the neg camber in the back.

 

I just bought new tires yes. The vibration started after the new tires i guess, hard to tell, i've had them for a while but it's the first time i drove for a longer period and exceeded 70mph
But the "sliping away" has been there for a while
When i bought the car (used) the springs on the passenger side had "clamps" in them, you know the factory ones to keep it at ride height. Could that have anything to do with it?
I'm not sure what to check on my suspension....

 

If your tires are fairly new you may have "thrown" a weight after the install. Leaving the spring spacers in has no long term effect (unless you don't remove them ). Make sure you have all your lug nuts and the tires are mounted properly (i.e. torqued). Lastly might want to verify your tire pressures.

Utah

 

Do you have the OEM wheels on the car? Make sure they didn't mount one of the front wheels on the rear of the car, it won't seat properly on the rear hub.

 

No, aftermarket wheels. Stern's, 18x8 front, 18x9.5 rear.
Would an "imbalance" of the wheels cause the rear end to slide away in a turn? it's like a "wobble" througout the entire turn period...
My search also opend the question of needing a hub centric ring and checking the suspension mounts. Suspension mounts?????

 

Do you have the proper lug nuts that should be used with the aftermarket wheels?
There are different designs.
Tapered , ball (OEM) and probably more.
They should not be mixed because they dont seat properly and may cause an unbalance, may even loosen while driving

I have some personal experience with the wrong type of rear tire.
The tires were to flexable, they had multiple radial grooves with cuts in them making the contact patch flex during lane changes, very uncomfortable, close to scary (simular to your story)
Going back the the (rear) tires I had fixed it instantly.
Not having the same type of tire front and back also had something to do with it.

Without hubcentric rings you'll have to be extra carefull mounting the wheels on the hub, use the criss-cross pattern for tightning and tighten in SMALL steps.
It goes without saying that the proper lug nuts HAVE to be used at all times.