383 SBC to LT1-T56 HELP

In 2015, My 1969 chevelle had a th350 mounted to the back of the 383 stroker 1987+ sbc 1-piece rear main seal. Then I installed an LT-1 T56 transmission and flywheel from a 1994 trans am in place of the TH350. I Did not drive the car.

Then the car got flooded (over the top of the engine) in Hurricane Harvey. Days after the flood water receded, I changed all the fluids, ran the car and changed them again. even drove the car around a field, hesitantly.
Car sat for 4 years.

Now when I drive the car it shakes and shudders when in gear, idles and revs fine when not in gear.

I have a feeling I have the flywheel clocked in the wrong position, an unbalanced flywheel in need of counter balance weights, maybe the wrong fly wheel, or the trans is toast some how?

please help

If it makes a difference, I believe I used the LT1 flywheel and bell housing that I got with the T56 transmission

An LT1 flywheel will not work with a 2pc rear main seal 383. LT1 flywheel will only work on an LT1. It is also ext balanced but using a different weight than a 400. Also it’s a one pc RMS. So if you used the LT1 flywheel that’s a problem right there.

Question is do you have an internally or externally balanced engine?

My car has a 406 with all scat rotating assembly and I really thought it was internally balanced. But when I pulled off the flexplate (was an AT car) I saw the weights and realized the flywheel I had purchased was wrong. I ended up buying another one with the correct 400 ext balance.

This may be your issue. Although seems to me it would happen in neutral too?

Do you have the old flexplate ?

Update

The motor is a 1987+ 1 piece rear main seal, 383 stroker, externally balanced

TCI rattler (internal) balancer on the front, original LT1-T56 Flywheel on the back

flywheel is 153 tooth with weights on it


I don't have the old flex plate with me, I may have sold it years back. When I had the TH350 auto in the car I never had any shaking

It still won’t work with the LT1 flywheel

The LT1 is a unique external balance. Not share with any other SBC.

You need a flywheel for an ext balanced 383/400 with 1 pc rms.

Like this one

https://ramclutches.com/apps/chevy/b...eels/1509-2509

Note the LT1 flywheel is unique. Also externally balanced but entirely differently from a sbc 400 which is what you have. And what I have btw.

This is the flywheel for the LT1. It will ONLY work on that specific engine 93-97

https://ramclutches.com/apps/chevy/steel-flywheel/1554

I went with the 2pc RMS version of that first RAM flywheel but in 168 tooth set up for a 11” clutch. Works great. Nice unit. Price was decent. 24-25lbs billet steel is a nice compromise for a street car. I don’t like the heavy stock type 32-36lb flywheels personally.

That does look like it will work.

Will I need to get a new clutch andstarter also? I ask because the LT1 flywheel is dished and the teeth sit closer to the starter than a flat starter would (or so I imagine).

Attachment 168774Attachment 168775

That I don’t know. Starter is a starter I believe. Don’t believe there is a LT1 specific one. Check PNs on rock auto to make sure.

Also not sure bellhousing will work. I mean it should work.

Clutch will work if you get a flywheel with the same bolt pattern. Check what you have - most of these aftermarket flywheels come with 2 bolt patterns so you have some options on the clutch.