Help with vibration (already searched)

OK, so I already did a huge search and turned up nothing. My problem seems to be different than what everyone else is experiencing. It goes like this...

Vibration occurs above speeds of 80mph or so. It is felt though the car body, shifter, and clutch pedal. Its quite extreme. You can feel it in the clutch pedal when you just barely have your foot touching it, not depressing it at all. Now here's the kicker - vibration goes away when I push in (disengage) the clutch. Let the clutch out (still at 80+mph) and the vibration returns.

I'm really thinking its not my DS or U-joints or gears or tires, since disengaging the clutch doesn't make them spin any slower. The car has a Pro 5.0 shifter, SLP clutch package, 4.10 gears, stock steel DS, and poly trans mount. That's all the mods that should matter.

Any ideas?

i'm very interested to know what you find. my 95 firebird does the same thing at and above 80. i hope someone can shed some light.-- i know this does not help, but interesting we both have a strange vibration.

Changing the load on the DS could very easily change its harmonics and cause it to stop vibrating.

My money is on the DS.

what if the ds is sending the vibration through the tranny and engine. hence when you push the clutch and disengage the tranny the vibration stops.

i would put money on the ds.

did you try it with the clutch out and rolling out of gear.

I notice that above 4000 RPM I get vibration. With the automatic, 1st gear is too quick to notice it, nobody but me would notice it in 2nd, but 3rd gear it vibrates like crazy once you get up there. Sounds like it's coming from the shifter.

I'm guessing it's the driveshaft, but my car came with the 1LE shaft.

So at 90-100 mph in 3rd at WOT I get vibration, but at 100 mph in O/D, no vibration.

well, it looks like i better get the drive shaft looked at.:(

it cost me 50 bucks to get mine done.
make sure they do a high rpm test.
mine was spun up to 10,000 rpm.

why does it cost so much? i mean i will take the drive shaft to them off the car. i can get my tires roated and balanced for less than that.

well, i broke down and went to a drive shaft specialist this morning. everybody i talked to said he knows his stuff. real nice person. we took the car for some hwy riding and he told me i needed u-joints,trans mount and ds balanced. $85.00 labor +parts. he also told me my rearend would eventually need some attention. always something:rolleyes:

he did tell me i had a strong motor. that seemed to impress him:D

thats not bad. i paid half of that for 1 u-joint.