What could cause a bad vibration in a 727 trans
while the vehicle is in neutral, not moving?

What is spinning inside the trans, with just the engine running. Vehicle is sitting still.

could the torque converter be going bad, or could it be the front pump

Is this a new combo or an old one with a new problem? Because it sounds like the wrong convrter weights or lack of them.

Is it all the time, or just when you rev it is n park or Neutral?

I had a similar issue, my 360 / 727 vibrated when reved to 1500 rpm or above, in P, N and D (felt like the trans was going to come right through the tunnel into my lap!)

the 3 of the 4 bellhousing bolts were loose...so might want to check those!

Jason

Is it a new engine ?

My Challenger was originally a /6 904.

Rebuilt a 360, Had it balanced, 727, rebuilt
torque custom built with 2600 stall. I have been trying to fix this vibration for awhile.

Torque does have the balance weights on.
Driveshaft is new and balanced, new joints, all
new motor mount and trans mount. new bushing on tailshaft.

This vibration can be made while sitting still
reving the engine up to about 3500 rpms.feels like in the trans tunnel

SAME problem going on! Just rebuilt the 69 340 and dynoed it ran strong on there and now that its in the car my brother says it has a bad vibration.. new 2400 stall converter with no weights on it, new dorman flex plate too. 04357 think is the number.. what could be going on?

hi
wrong / defective flex plate,didall the bolt holes line up on installation ?

convertor not balanced , does it have weights on od of body , not front engine side ?

wrong or bad harmonic balancer ?

bad trany mount or bad motor mount ,,

engine plug wires crossed

just some places to look !

Looks like it was just the open headers under the floor boards!!!.Now that the the exh is hooked up again all is good from what i hear from him!. With everything that has went on with this car I think he was just being over cautious!
thanks guys!.. Hope to maybe get some video for you all!