Whats up! I've been having a bit of trouble i have a massive vibration that begins at 2000 rpms and dies off under load untill 3000 rpm then its a eathquake inside the vehicle. The motor was rebuilt stock crank stock rods stock heads 30 over trw pistons 10:1 t-10 4 speed stock rear..... What i've done:had the trans checked 3 time,new balancer, new flywheel, new cap and rotor, new wires, new coil, new distributor, new plugs, checked for vacuum leaks, checked for missfires under loads, i had checked the flywheel weight to the weight on the original gm flexplate that cameoff the motor it was dead center, i have also checked my exhaust for excessive back pressure. p.s. the motor vibrates in nuetrul even at a stop while in gear.. If anyone knows if tis is normal please let me know and will it whipe my bearings Thanks Elie

Uh, definitely not normal.
If it's shaking in neutral, and you've checked the balancer and flywheel - then it's inside the engine.
Did you have it balanced?
I'm guessing something went wrong. Left a piston out or something REALLY big and heavy. I know you can't get the oil pan off with the T-10 in there, so I think you're going to need to pull the engine out and pop the pan off and see what's going on.

Side note - when you changed the plugs, was anything amiss with any?

the balancing was done at the machine shop as well as the block and crank, piston pins rods and bolts.I assembled it i know that all eight pistons are in there i had done a compression check they all were 190 psi but i have done a checkwhere i had removed everything up to the flywheel and started it it was smooth and then i installed the clutch and it was smooth then the bellhousing and trans and it was smooth when i put the crossmember and exhaust up and put the car on the ground it felt like a WOBBLE at 2000 then smooths out to 2800. at 3000 i can hear my plastics rattling and also hear the vibration through the sheet metal of the car witch is pretty intense. after a 10 min ride cant feel my legs p.s. it dosent shake from idle to 1800 at all thanks Elie

You can only use a flywheel and front damper made for the 400 sbc. This engine is externally balanced. If you used the ones from the old 350 that is your problem.

hey! i have a brand new externally balance flywheel and balancer.....But i have heard thet the 454 and the 400 are a very close balance and the might have packged a 454 flywheel instead of a 400 fywheel, so i am going to get a new flywheel and try it out and hope for the best..Thanks Elie

Did you ever get rid of the vibration?

its your flywheel

I had my Torque Converter replaced with a stock replacement for a vette, the vibration is now gone.