Torque Converter Balance Weight

[TB3Barracuda340]

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.

 

[Mr Cuda]

That weight is way to big.
Looks like the one piece 360 weight.
(Early 360 are dual weights)
The cast 340 uses the smallest of counter weights for any mopar. For starters, twist that off and run none until you can weld the right one on.
I will get the spec from the direct connection manual and update.
Maybe a picture too, as I have the one from mine. I zero'd the rear onky for a flywheel.

 

[TB3Barracuda340]

Thank you.
I had found pics of different counter weights on TCI's website, and it stated that the butterfly weight was used starting in 1977. I didn't occur to me until recently that there were no 340's in 1977, so that probably wasn't the correct weight.

 

[pschlosser]

maybe don't operate it anymore until its resolved. you don't want premature wear on the crankshaft bearings.

 

[TB3Barracuda340]

Agreed.
I drove it 3.5 miles on Thanksgiving and knew something wasn't right. That was the first time that I had driven it. I haven't started it since.
I'll look tonight at removing the weight.

 

[pschlosser]

Agreed.
I drove it 3.5 miles on Thanksgiving and knew something wasn't right. That was the first time that I had driven it. I haven't started it since.
I'll look tonight at removing the weight.

I guess removing the weight is all you can do. Having the correct weight or a torque convertor with the correct weight seems like it would be better, albeit more time and expense to find one.

I'm curious about the Direct Connection document @Mr Cuda mentions in post #2. Let's see how that works out.

EDIT: If the engine (rotating assembly) was balanced without the TC, then I'm guessing no weight is warranted. But again, that's just a guess. Your motor builder may be able to weigh in (ha ha) on that one. If you swapped out the harmonic balancer used during the rebuild and balancing with an OEM one, you may want to put the rebuild one back on.

 

[Mr Cuda]

The direct connection tech sheet was for modifing a flywheel for a counter weight engine. So the reference for drilling holes in the flywheel, means you have to add that weight on the opposite side for a converter.
Our old torque flite expert (Mr Pat Blais) had a pattern to position for welding weights.
I'm sure one is out there.
340 had 4.22oz of imbalance, and the 360 had 19oz.
I bet it shook.
The electro spot welds for the weight are strong for prying but not twisting.
I have put a giant cresent up in there with the splash sheild off, and just twisted them off.
I will still look for my 73 cast converter.

 

[Mr Cuda]

Flex plate is clocked, so converter only goes on one way.
77 360 converter got me thinking, its only a mid stall. Not a high stall. Last year of true high stall i think is 75.
The mounting lugs are different, so easy to tell.
Here is my cast 340 converter with 2 small metal square by the drain, and an early 360 with the dual weights to compare.

 

[TB3Barracuda340]

Thanks for all of the help. After removing the splash shield to better access the counter weight, it appears that it is welded on the sides (and maybe on the top), so I don't see any other option other than dropping the transmission so I can gring off the welds to remove the weight.

 

[pschlosser]

so I don't see any other option other than dropping the transmission so I can gring off the welds to remove the weight.

Yea, I thought that was a given. I was not even aware the weights could be removed without separating the transmission from the engine and dropping it for access. Nice tip, Mr Cuda.

If your crank and rotating assembly was rebalanced during the engine rebuild without the (correct 340) torque converter, you may not need another counter weight, only to remove the (wrong) one that is there and grind down the spot welds. As I said in post in post #6, you may want to put the harmonic balancer it was balanced with back on, because this SHOULD be less guess work.

But you may want to have the rebuilder weigh in on both the counter weight and which harmonic balancer. They will know if the crank was rebalanced with or without the T/C counter weight. If they balanced with with a presumed counter weight, they can tell you what (offset) weight it was balanced for.

If it was NOT rebalanced during the rebuild, presuming the crank is still factory configuration, then use the factory counter weight mass on the T/C and the factory harmonic balancer. I detest guess work, but what can we do, without definitive recommendations by the rebuilder?

 

[Mr Cuda]

If you are pulling the trans, do you also want to upgrade to the correct high stall converter?
When the engine was rebuilt, did they tell you anything about the balance, or compression?
That converter shown is available. Shipping is what it is. Cast crank 340 convertor weights are not common.

 

[pschlosser]

Cast crank 340 convertor weights are not common.

You'd probably have to fab your own. Using a hunk of similar metal and a digital balance (scale) cheaply sold on Amazon.

Upgrading the convertor is a nice recommendation. Well done, @Mr Cuda

 

[Mr Cuda]

Converter weights are not a straight weight measurment.
There is no way that the correct 340 ones weigh 4.22oz or that a 360 one weighs almost 20.
There is some kind of math using circumference.
Beyond my need of knowledge.
I do know it was exspensive to have mallory metal to zero balance just the rear of my cast crank 340.

 

[TB3Barracuda340]

If you are pulling the trans, do you also want to upgrade to the correct high stall converter?
When the engine was rebuilt, did they tell you anything about the balance, or compression?
That converter shown is available. Shipping is what it is. Cast crank 340 convertor weights are not common.

Absolutely! I just wanted a solid streetable transmission when it was rebuilt. I didn't really give any thought to the TC. He just supplied one, so I used it.
I have attached the build sheet. I will reachout tomorrow for more specific info

 

[pschlosser]

Converter weights are not a straight weight measurment.
There is no way that the correct 340 ones weigh 4.22oz or that a 360 one weighs almost 20.
There is some kind of math using circumference.
Beyond my need of knowledge.
I do know it was exspensive to have mallory metal to zero balance just the rear of my cast crank 340.

The digital tools I've seen used to balance a rotating assembly can, indeed, tell you the offset mass the crank is "off balance" be it 1.24 ounces, 13.675 grams, etc.

I cannot say every balancing shop uses this kind of tool, but in my observation, some of them can.

The crank is often balanced with only the harmonic balancer installed, and optionally, the torque convertor. In some cases, with an "internally balanced" crank, without even the actual harmonic balancer.

 

[TB3Barracuda340]

I talked to the engine builder today...he says somewhere between 10-10.25:1 compression and the crank was balanced with the stock engine damper.

Any converter builder reccomendations? I'm waiting to hear back from a local builder, Biltrite Converters

 

[Mr Cuda]

Ok. So balanced with no flywheel or converter attached, we have to assume what?
Stock 4.22 counter balance, or zeroed?
Until you know, we are all guessing.

 

[pschlosser]

"balanced" implies zero offset weight. So, no weight on the TC.

The digital crankshaft balancing equipment can, indeed, balance to some offset weight. For example, a crankshaft can be balanced to a 120 gram offset, that is not attached nor present at the time of balancing. But, unless you are told the weight it's been balanced, you can presume it's zero.

 

[Adam]

Since they supplied you with a 360 balancer maybe it’s a 360 converter… but here is a bit of trivia to store in your brain for future projects. 93-95 Magnum 360 converters had balance weights on them… they are NOT the same as an LA 360. After 95 the Magnum used a neutral converter with a weighted flexplate. So if ordering a 360 converter make sure of the distinction.

 

[Xcudame]

Usually for a cast crank external balanced engine, an engine balancer will want the crank, bob weight, harmonic dampener, and flywheel or flex plate/torque converter. It would be hard to balance a cast crank engine with just the harmonic dampener unless they used heavy metal in the crankshaft.