And yes I swapped in a single piece driveshaft. I don't think its the u joints because that would change with speed, not with rpm fluctuation.

 

You kind answered your own question. The only part of the transmission that turns in sync with the motor is the clutch and the input shaft unless your in 4th gear. So if the vibration seem to be going with the engine that eliminates most of the drive line.

 

Probably input shaft bearing. How old is the trans, and how hard to you beat on it?

 

How many miles on the U-Joints?

 

Input shaft bearing? I didn't know there was such a thing lol so it has to be my clutch or input shaft bearing right?

 

Fyi, the reason for the 2-piece driveshaft is to absorb harmonics/vibrations from your 3.4 engine. It actually serves as a vibration damper. If that's what you're feeling, and it started at the time you swapped driveshafts, then you're just now "feeling" what was already there. Or, it could be that the front of your driveshaft is bottomed out on the tail housing of the trans (need to check with all the wheels on the ground). Did you lower your car? That will drive the slip yoke further into the trans. If the slip yoke is bottomed out, you will feel some bad vibes.

 

I'll check that. I just didn't think it would be the driveshaft because it fluctuates with my RPMs. Not with my speed. Hell I can go 100 and there's no vibration as long as I'm not in gear.

 

Putting the drivetrain under a load changes things. Torque from the rearend could be pushing the driveshaft forward even an itty-bitty bit. If the slip yoke is close to zero tolerance as it sits idle, that little bit of torque movement would be enough to bottom it out. Hitting dips and bumps in the road will bounce the shaft forward as well. At rest, the slip yoke wants to be slid out at least 1/2" from all in, to allow for suspension travel.

 

Okay but the reason I'm skeptical about it being the driveshaft is because, even if I'm not accelerating, it vibrates.

Even with the clutch fully depressed, it vibrates as follows

1st gear: anything above 17-20mph
2nd gear: anything above 35mph
3rd gear: anything above 60-65mph
etc...
etc...
I can be cruising at 35mph, while holding the clutch to the floor and put in 2nd and have a nasty vibration. Keep in mind that I'm holding the clutch in through the whole process of pulling out of 4th at 35pmh and putting into 2nd. I can put it in and out of 2nd while cruising at 35mph and the vibration comes and goes as I put the car in and out of gear with the clutch in. As soon as I pull the shifter into 2nd, the vibration is there. As soon as I take it out of 2nd, it goes away. This happens with every gear...
It seems to me like IF my RPMs were to be high when I go into gear, it vibrates, even with the clutch in and the RPMs at idle. Because at 35mph, my car would be at about 3000-3500 in 2nd gear. Also, it doesn't happen at just 35mph. It happens from 35mph all the way up to the max of 2nd gear, just as it does with all of my other gears too. I don't know how else to explain it but I'm sure it's not the driveshaft. I just pulled it onto a lift and the driveshaft has a decent amount of room before it bottoms out on the tranny. And its a lift that you drive up onto. Not one that lifts the car by the frame.

 

Jeez, that's a lotta "stuff" to process! Ok, good about the driveshaft clearance anyway. You get the vibrations when the clutch is depressed, and the car moving right? Do you get the same vibrations while sitting idling, or only when the car is in motion?