727 Vibration

Tech Question

jason guitar, milan, MI, 1970, ply, cuda, 440

I have a 73 cast crank 440 motor in my 70 Barracuda and my 727 trans and/or converter grenaded. I had a another 727 from a 71 New Yorker rebuilt and instaled a new converter from GER (2400 stall). I replaced the flexplate with special one from B&M (#10237). I put it back together, now I have massive vibration. So I welded the weight off of old converter with stock flexplate and that helped a lot but still quite a bit of vibration in 4000 rpm and up range. I forgot to check concentricity error. Could that be the problem? I hate to think i have to rip apart my freshly reuilt trans to check this. Ughh!! Thanks, Jason

Jason,

chances are that you are on the right track. You seem to have proven that by your initial partial repair attemp. Poor concentricty will just wear out pump bushings and the converter hub (and maybe eventually crack the hub) but will cause very little in the way of vibration.

Did you remove the original weight from the GER converter berfore installing the chopped-off one? Was the GER one(s) large? On cast-crank dampeners, the weight has 2 jobs: (1) balance the converter (same as the small weights typically found on internal-balance converters) and (2) contribute to crankshaft balance (the lion’s share of the weight.)

Then there’s the clear possibility that the weight may have been welded on a few degrees off, too much “weld” weight, etc.

The B&M flexplate should have done the job, but their catalog seems to show too few part numbers to cover all the possibilities. (There are 5 possible permutations in all.) So maybe it was simply the wrong one.

I’m for reinstalling the weights that came on the new converter, then getting the MP weight package P4120241 and following the instructions to a “T”. Or, the other “out” is a known-good cast-crank 440 stock converter.

Rick