46RH Vibration ????
 

Guys,
I have a 46rh sitting behind my 340 in my 1934 Plymouth tudor rod.
Pretty much since I got the thing running I've had a vibration primarily at higher speeds.
Its been driving me mad trying to locate it. So I'm now posting up the details hoping someone may know more about this that I do.

So far I have -
Jacked the rear of the car off the ground and removed rear wheels, put nuts back on to hold brake disks. Ran the car vibration still there. Not wheel balance.
Removed the tailshaft and put a spare yoke into the output of the trans. Ran the car vibration still there. Not the tailshaft.
Place trans in neutral and park. Rev engine up to 4500 and everything is smooth. Not the engine or converter.
When running trans with dummy yoke inserted vibration starts at about 50mph. If I shift into 4th gear and with TC locked vibration still there but maybe slightly less evident. Could it be something internal to the trans ?
Seems to be speed related as it happens in 3rd or 4th once speed gets high enough.

So I'm thinking its the trans somehow ??
Could this be related to the bands being too tight or something ?
Trans is newly rebuilt with only a few thousand km's on it. Converter is also new and is a ProTorque unit so I'm not questioning the quality of that.

Any suggestions anyone ?

I take it, That this started after the trans swapped/rebuild. But that all was fine and good before the trans was rebuilt?

Motor and trans installed together. They have never been run prior separately.

I did notice, if holding a steady state rev's at just under 2500rpm I get a lot of vibration. If I then lock the torque converter at this point the vibration reduces, but it is still there.
Thats not changing gear or anything, just locking the TC.
Torque converter is a new ProTorque unit and I cant see them not balancing it correctly ??

Does your 340 have a steel or cast crankshaft?

I would have to say that it (The Problem) is a Rotating Assembly Balance issue. You Might, and I mean might, just might get lucky and if you put a Fluidampr on it, could get it to leave you alone.
You could send it back to the machine shop for correction in the balance.

Its a late 340 (1973), so its a cast crank with external balance. Running the original counterweighted harmonic balancer. Flex plate is an external balance B&M unit with the segment cut of it.
Converter is a neutral balance.
Rest of motor is original. Original 4.040" pistons, original rods etc. It was freshened up with a light hone and new set of rings onto original pistons and basic gaskets etc. It was not re-balanced when this was done.

Thanks that's what I was after, the only thing you can do is make sure the flex plate is correct and the motor is balanced correctly.