I just installed a 383 this weekend and now I have some harsh vibrations 3,500 rpms and above. It will do it in park or in drive. Low RPMs is fine but anytime you bring the revs up it will shake the whole car.

The rotating assembly was internally balanced front and rear, so I just knocked the counterbalance weight off my stock flexplate. Harmonic balancer/hub was installed per the procedures in the FSM.

I don't think its a misfire as the motor runs fine. Anyone got any suggestions what to check out first TIA

 

Dude why did you knock a weight of your flexplate???? When you had your motor done...did you take you flexplate in with the harmonic balancer??? If it was balanced correct they should have asked for it.

Anyway I thinking its the balancer or flexplate. Who installed you crank hub???

 

Crank was nuetrally balanced so they didn't need my flexplate when the motor was balanced. I installed the Hub myself and fllowed the FSM proceure to the T to make sure it went on right. I'm going to swap flexplates this weekend to see if that helps.

 

I just had my forged 383 done and picked it up last week. He asked for my flexplate and balancer. Hold on gonna check my flexplate. Okay....he took all the weights off the flexplate and drilled 3 extra holes in it and appears to have made small drill mark (4) to take off additional weight. Mine was internally balanced also....took some metal out of the crank (Eagle 4340) and added some heavy metal in it.

as for me....I just put in the pistons last week and hopefully gonna throw in the motor this weekend.

good luck.

 

it could be anything really....

is this an automatic or a standard car?

i had similar problems myself, with the orginal motor.
i had in mind a converter problem, but it seemed to fixed itself

 

Had the same thing happen to me..Just get the flywheel nuetrally balanced and you will be fine

Cody

 

Wouldn't removing the counterweight off the flexplate accomplish the same thing?

 

Dude...its not like something you can just guesstimate. My flexplate got like 4 drill marks on it from the balancing. Drill marks as in looks like he punched a drill only half way through to get the desired weight removed.

 

THe 4 marks are probably from the drill bit he used to drill off the counterweight. I have the exact same marks on my flexplate from when I did it.

 

Yeah ......but there are also nemerous other holes he drill to offset that. (ooops left that out)

 

Yup..the guy that did mine had to drill 4-5 holes also to balance it out..

You really dont have to trust us unless you want to deal with that terrible vibration and the chance of really messing your bearings up

Cody

 

I would get the Machine shop that did the work and see if what they reccomend. It seems odd to me that they didnt want all the reciprocating assembly when they did the balancing, especially considering the application. I would deffinatly find out what they reccomend doing so that it can be on their head.

 

I'm starting to think the assembly wasn't actually internally balanced. I'm going to throw a stocker on tonight and see what happens.

 

A neutral balance flexplate should do the trick. What heads will you be using? Who built the motor?

Thanks

 

Stock LT4 heads for now.

I bough the rotating assembly used off a board member here and than had a local machine shop do the block work and assemble it.