I have a pretty strong vibration coming from somewhere in the first half of the driveline (before the drive shaft).

In park/neutral, the idle is fine, but the after the engine starts spinning past 1,500 RPM the car starts to shake pretty hard. The interior rattles some too If I'm under the hood and open the throttle at the throttle body the engine will vibrate some, but it doesn't buck like something's the matter with it. All the cylinders are firing fine (fuel/spark).

In drive the vibration really isn't that noticeable under acceleration and most cruising is done at such a relatively low rmp range (sub 2k) that I don't really notice it. If I drop the car into a lower gear the vibration rears it's ugly head. Either the transmission or rear end also makes an angry gear sound when I downshift and engine brake. It’s not a grinding sound like missing a shift in a manual, it’s just a loud whirr that gets louder the lower the gear (it's the loudest in 1, loud in 2, not that bad in 3, gone in od). It’s also only present when I’m off the gas and engine braking.

Both the engine and trans have 106k miles on them. The previous owner claimed that the trans was rebuilt 10k miles ago when I bought the car (20k now). Judging from the state of the rest of the car I doubt this is true (he had no paperwork) and if it was rebuilt it was probably pretty half-a**ed job.

The engine has never been rebuilt. At some point, someone had the heads off because there are aftermarket gaskets on them. I've never been inside the engine. I did a complete tune up myself a few months ago when I was trying to figure out why it was running rich. Injectors, cap, rotor, plugs, wires, filters, etc. While this did help the car to have quicker throttle response (and got rid of injector tick along with the cold start ), it did nothing to either help or hinder the vibration.

Any ideas?

 

pull the inspection cover and check for a cracked flexplate or loose torque convertor bolts.

 

Good idea, I will do that in the morning. What should the bolts be torqued to?

Bonus points for the fast reply