Massive Shaking @ 80mph +
 

What are some possiable causes???

I was thinking the drive line, maybe a new driveshaft, or something?

tires are probably outta balanace, they new?

no they are not new, i just bought thsi car, so they probably are. I was plan on having some new ones put on , so once I do that i'll see if that fixes the problem, if it doesn't what could be some other possiable things to look at?

I don't think that the tires could cause violent shaking. I would say look into the driveshaft and driveline.

Give more information. Did it just randomly start or has it always been that way.

May be the driveshaft if not the tires are in balance.

i've only had the car a week, I don't know much about it, im finding out as I go

Well I got screwed when I bought my car. It had the same problem turned out when I pulled the cover on the rearend it was missing 2 teeth off the ring gear. Though you should check all the more likely possibilities first.

Chances are it is a warped rotor or unballanced tires. Our drivesahfts aren't the smoothest either at high speed.

If the vibration is very high-frequency (feels like you're inside an electric shaver) it's probably driveshaft/u-joint related. If it's a lower frequency shake where you can basically feel every pulse it's usually wheel/tire related. If it has the shake just revving the engine up in neutral it's somewhere from the tranny input shaft forward.

If the driveshaft has been out of the car, then it may have been reinstalled 180º out. Try dropping it out and spinning it 180º before anything else. Just might work, and doesn't cost anything as long as you have a 7/16" wrench ;)
*NOTE*
I would jack the car up by the rear, to help stop trans fluid from leaking when you pull the DS out of the yoke. Set parking brake, and chock the front tires. (You don't want that car coming down on you.)

*EDIT*
While you are under there, you can see how much play is in the U-joints too. A little is okay, but if they are really sloppy, then plan on replacing them soon.

it's more like volient shaking, like the dash and the whole car starts shaking...

I will look into that.. thank you :)

I parked my car for a while and only ran it at the track. When I would "take it around the block" once I got up around 70, the whole car would violently shake back and forth like when you stand at the back quarter and push towards the other side and make the car rock back and forth. Only it would do it at 70mph down the road, F*CKING Scary!! Let me tell ya. Anyway, turned out to be dry rotted tires.

Get your tires balanced.

I went through this for a while right after I had my entire suspension redone - Spohn all the way, rebuilt tranny, and a Moser 9". It was a real PITA, but it was eventually fixed... exactly how, I don't know.

I balanced the tires, didn't work. Had a custom made steel driveshaft put in, didn't work (but it is very nice). Had good gears and Moser axels, obviously not the problem. However, when I blew up the tranny for the second time, and had it rebuilt a little better, it went away.

Now, I am not positive on this, but I believe it was the torque arm or something connected to the tranny that wasn't exactly lined up true, a fraction of an inch maybe. I think my tranny guy didn't quite line something up right, and it caused the vibration at high speeds. It was a real PITA, I couldn;t even listen to a CD, it would ocnstantly skip. But when the tranny was taken out and rebuilt again, all was well.

But, the same symptoms can come from tires out of balance, bad u-joints, bad driveshaft, bent axel, bent wheel, bad gears/bearings, bad pinion angle. Anything can cause vibration at high speeds. Take my list and start with the easiest to diagnose, then start fixing/replacing stuff that is cheapest, and work your way up till you solve the problem.

BTW - this is the perfect time to do any mods you may be planning to do. For example, if you think it may be the gears, put in some 3.73 or 3.42 and a good posi. Or if you think it may be the driveshaft, get an aluminum or a new good one put it now. Also, if your tranny is toast, no harm in rebuilding it. But the cheapest thigns to check are the u-joints, pinion angle, trans mission mounts, and torque arm. Make sure all are lined up right. Good luck figuring it out, this is a PITA, but well worth it once the problem is solved.

my gta used to violently shake around 70 mph. After i put my rims and tires, the shaking was gone. I say get a set of new tires and see if it will still shake

Auqatreads that are put on backwards will do this - but the old owner warned me that the passenger tires were mounted backwards so I knew what to expect. At 65 or so, the car would shake and stuff. Remounted them and the shaking went away.

Now I've got something like that on the beater Firebird, but I'm thinking it may be the driveshaft. Hard to tell how fast I have to be going for the shakign to start, as the speedometer is not working right and the car has trouble getting out of its own way, let alone going fast.

dont forget about the front end too. if something isnt aligned rite or somethin is worn out it will shake like hell. my 84 berlinetta threw the ball joints and if you got past 60 without shaking like hell you were lucky. after they were replaced and it was realigned, it alot smoother and i know it goes up to 80 without shaking. check the front tires for uneven wear (ex. the tread pattern slopes down from the outside in or cupping on the inside where lil indents appearing along the edge), make sure the wheels are solid ex. theres no free play like something came loose, and see if you can visually see if the tires themselves arent oddly sitting ex. not straight up and down or toe-in not way off. id also check everything else everyone stated like tires themselves and driveshaft cuz those can be the culprits too

I'd say Tire Balance, Alignment, Crank, or Driveshaft. Possibley a combination of either. I check tire balance and alignment first.