So I rebuilt my motor, took the engine and trans out and put in summit 3000 stall converter in it. Got everything working and once I got up to speed the whole car shook like hell. Its bad at around 55 mph and if you step on it the shakes get increasingly worse. It not really noticeable around town, I do think part of it is engine related but that can be tuned out.

I'm thinking its torque converter because that's the only thing that's changed. Engine runs fine enough that it wouldn't cause a violent shake.

Attached is a video of the shake at idle

Cammed 5.3 lm7
Turbo 400
adapter flexplate
Summit Racing Torque Converters SUM-G2698

Thank you for your time
God Bless!

 

Were the crankshaft or harmonic-damper changed as part of the engine rebuild?
The flex-plate you installed could be an issue if it has a counter-weight... The same goes if you changed the harmonic-damper (balancer).

Damn that is a crappy torque-converter. Sorry...

Which flex-plate and adapter are you using?

The flex-plate mounting pads must be properly spaced away from the flex-plate, where the mounting bolts go.
The instructions that were included with your torque-converter go over this... It states that a 1/16" to 3/16" space must be established.
Use washers as needed... Splitting the difference to 1/8" spacing would be ideal.

Once the flex-plate to torque-converter spacing is established... the torque-converter pilot must be inspected...
To ensure it is centered, and supported by the opening in the back of the crankshaft flange or adapter.

Simply not having the torque-converter pilot centered and supported will cause an "Out-of-Round" Vibration...
This can do some major damage if left as is.

 

Yes, I replaced the balancer because I broke a tab while pulling it off. Replaced it with a factory gm one.
Planning to buy a new converter cause I need to take the tranny out anyways.


This is a similar flex plate to what I have. It doesn't require a spacer. Starter works fine so im going to assume its correct.

 

Is that a flat flex-plate or a dished flex-plate?

The 4.8L and 5.3L engines will normally use:
-A flat flex-plate with a spacer/ pilot extension assembly (The spacer goes on the between the crankshaft and the flex-plate).
-A dished flex-plate with a spacer/ pilot extension assembly (The spacer goes between the flex-plate and the converter).

It is possible for the starter motor to engage the flex-plate teeth... but have a mix-match that results in the converter pilot being unsupported.
What was the flex-plate to torque-converter spacing?

 

So I have a dished flexplate and I don't think I have that pilot extension in it. Jacked the car up and pulled the bolts out of the the converter and flexplate and the converter pushed back one click. Theres about a 1/4 inch gap between the converter and the flexplate now so thats wierd. I don't recall putting that spacer in it so I think thats the main issue. I think I still have to pull the tranny which is fine.

Is it going to be an issue to have space between the flywheel and the converter using a spacer in between the bolts?

 

Be very careful!

If the torque-converter is too far out of the transmission... the oil pump in the transmission will either break or not be engaged.
Very bad!

If the torque-converter pilot is too far out of the crankshaft pilot support... vibration and damage can happen to all 3; engine, converter, and transmission.
Very, very bad!

Unless you have a custom torque-converter made; for the purpose of pairing a Small-Block Chevrolet Gen. 3 or Gen. 4 engine to a THM400 transmission...
A dished Flex-Plate alone, will not permit the torque-converter pilot to be supported by the crankshaft.
Note: some Gen. 3 truck 6.0L engines were produced with a crankshaft flange that is like a Gen. 1 (One-Piece seal type) engine and does not require a spacer.

Purchase the GM crankshaft to flex-plate spacer/ pilot support extension with longer flex-plate bolts.
Measure the torque-converter to flex-plate spacing (like the instructions with the torque-converter say to do).
Reinstall and pray that you did not do major damage!

Spacer= GM part #12563532
Bolts= GM part #12563533 (six bolts required)

These parts are available at both Summit Racing and Jegs.

They are available at your local Buick-GMC, Chevrolet, or Cadillac Dealership Parts-Counter as a special-order-part and normally will have the parts over-night shipped from a warehouse to the dealership... at no additional cost to you.

If you do not mind paying shipping... most all of the Online GM wholesale websites will sell you these parts for about half the dealership price plus shipping and same-state sales tax.

Good luck!

 

I haven't read through all the replies here but watching your video it looks like the converter is not engaged with the crank. That will cause the nasty vibration you described for sure as well damage your pump. I would start there to make sure the converter is engaging the crank correctly and report back.