Torque Converter Balance Weight

[marksmopars]

340’s that came with forged rotating assemblies were internally balanced and torque should be neutral balanced as well. Later 340’s and then 360’s were externally balanced. From the pics of the 340 unit it looks like some weight might be needed for neutral balance, depends on what year the 340 was that the unit is from. Later 340’s used cast as did 360’s which is why different balance specs.

I believe you indicated your engine is internally balanced at this point, this does point at the tc balance. Good luck

 

[TB3Barracuda340]

I've requested some additional information on the engine builder. He's waiting to hear back from the machine shop. I'm learning a lot in this process.
The engine is numbers matching. build date on fender tag is June 1. I don't remember exact date on engine assembly, but I think it was mid-May. It had a cast crank engine damper.
The transmission was replaced under the previous ownership. He thought it was rebuilt, but numbers indicated something from the mid-80's.

 

[pschlosser]

He thought it was rebuilt, but numbers indicated something from the mid-80's.

To some, that IS rebuilt. It's been customary for years, in transmission shops (example AAMCO) and service garages, to SWAP your transmission, for a rebuilt one. This allows them to complete the project in a short time, without the car occupying space on the lift for a day or longer.

 

[TB3Barracuda340]

From the builder: "No weight added to the crank."

 

[Mr Cuda]

This doesn't really clear up anything for me, to be able to help you.
No weight added.
Does that mean stock cast crank balance?
Does that mean zero balance?
Adding high compression pistons (10.5) does not make the need for counter balance go away with the cast crank.
All we know for sure is your current convertor weight is completely wrong.

 

[Xcudame]

Perhaps the transmission (and convertor) were "rebuilt"/swapped after the engine balance? This would explain the huge 360 type weight on the torque convertor.

Like Mr Cuda said, we still don't know enough to help. 10.5:1 pistons will typically be heavier than 8.5:1 pistons, so this would require more exterior (dampner and convertor/flex plate) balance.

You don't want to probably hear this, but the only way to correctly fix the problem would be to tear the engine apart and have the rotating assembly rebalanced. You might get close with a convertor balanced for a cast crank 340, but you're still going to be compromised.

 

[Cooter 14]

After reinstalling the rebuilt 340 and 727 combo back in my 72 Barracuda, I have a pretty terrible vibration. I thought I had it nailed when I replaced the aftermarket engine damper (that was weighted for a 360) that the engine builder installed with the factory rebuilt damper that I had sent with the engine. Unfortunately, wasn't much, if any better. I contacted the transmission rebuilder about the torque converter he supplied, and the guy that builds TC's for him retired and closed shop. So... I have a TC with no specs, no way of looking it up, installed in the car. I have a couple of pics of the balance weight. The engine builder (he only does MOPAR's) said he's never seen a counter weight that big, and has asked others, and they agree. Does the weight in the attached pics look like too big for a 340? Engine is the factory, late-72, cast crank. The transmission is a replacement and running the numbers, appears to be out of a mid 80's truck.

View attachment 132545

View attachment 132546

Yes is the wrong weight

 

[TB3Barracuda340]

I went directly to the source and called the machine shop. He did not balance the crank. It's just the original, cast crank that machined .030R/.010M So...I essentially have a stock rotating assembly, with replacement pistons. The piston weight is 720g.

I am hoping that I'm beginning to provide the correct information. Again...learning a lot in this process.

 

[Xcudame]

Here's what I'd do if it was my car. Since the piston weight is close to factory, I'd pull the transmission, cut the weight off the torque converter and replace the flex plate with a B&M one for the cast crank 340.
Then drive it and if the vibration is gone, enjoy it! See link for Mancini below.

B&M Flexplate

 

[Mr Cuda]

Sounds like you are pulling the transmission, no matter which way you go.
I will offer my very good condition 340 cast crank convertor, for your concideration.
It is a true factory high stall. Rated at 2400 give or take engine output.
Your convertor is a mid stall, approx 1800rpm.

 

[TB3Barracuda340]

@Mr Cuda
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