Car feels like it fishtails

[URSPANKED]

I have an '87 GN with the mods below. When "mashing the motuh" from about 50-60, as when passing another car, the back of the car starts fishtailing. It's not spinning the tires. It's as though one wheel grabs, then the other. It feels pretty squirrely when you get to 80 or so. Anyone else experience this? It almost feels like there's a problem with the positrac. It doesn't do this when getting on it from a stop or from a 20mph roll. It just gets sideways!

 

[GN1]

it could be your drive shaft if it only feels at high speeds trust me jus take it off and get it balanced it cost about 80 bucks

 

[GN87Mike]

Mine used to do the same thing when I had BFG Comp T/A's on the back. I thought it was the belts in the tires "walking". It would not do it at track with slicks or after I switched to M/T Street Radials.

Mike

 

[buickturbo-t]

Mine does the same thing. The car will sit there and float back and forth if I stand on it say at a 60mph, Scary as hell. At first I thought that it was the control arm bushings, So I put Poly bushings in and boxed the upper and lower control arms. It did get better but still does it. It won't do it when @ the track with my MT drag radials so its got to be the tires.

 

[suicide six]

Pinion snubbers installed?

 

[mikec1969]

Pull the rear shocks and check the travel. You may have one bad shock. Also, when you remove the shocks take them loose at the bottom first and note how far they extend after you remove the bottom fastener. It should extend a few inches past the lower mount. You should have to compress the shock to install it. If you only have to compress it an inch or so it means the shock is not correct for the car. I had a GMC van that had shocks that were too short installed from the factory it broke the shock mounts twice and always felt like it was on ice in back. We put a longer shock on it and fixed it immediately. Hope this helps.

 

[TurboTnZ06]

Mine did this. Feltlike I was on a boat going over waves or something. Then I replaced the limited slip - idiots at the repair shop put in a cheap Auburn "High Performance" unit thinking that my car didn't have much power...I went back a month later after I trashed that posi (it would only spin one tire) and put a better one in. Fixed the walking at speed problem and hasn't come back since.

 

[Race Jace]

this is interesting, we had that same problem with one of our cars. it never did it until we started running about 120 in the 1/4. the rear end was stock with dual airbags.

the first thing we did was box the lower and upper control arms and install polys in the lowers. this did nothing...

next we installed one of those huge ATR swaybars, this helped but it was still present.

then we went out and made several passes with several of us watching from the side lines. it looked like the tires were wavy really bad. (they were the comp t/a radials 275/60/15 on stock wheels) We switched the tires to slicks or drag radials and the problem went away.

I have a video of a truck on a dyno doing this to the tire. I don't know how to post it but if someone wants it e-mail me. It is a very interesting video.

 

[turbobuickman]

Just curious...would it be the actual tire causing the problem described or could it possibly be improper balancing?

 

[Race Jace]

deffinately not ballance....

 

[Sleeper-6]

My car did this a while back, changing out the 15 year old shocks for a new set of Bilsteins fixed it. Shure amde for some good looks from whoever was riding shotgun when you dropped the hammer. I was always afraid it was going to sway one way and just keep going at 50+ mph.

 

[URSPANKED]

Thank you all very much for your replies and help. I recently replaced the shocks all the way around. From what some of you have said, I'm leaning toward the tires. I have the BFG Radial T/As that have quite a bit of miles on them. I had BFG drag radials on it for a while, and truthfully, I can't remember whether it did it or not. Next on my list is new tires for the back. Thanks very much again for your help.