727 Too High RPM

Tech Question


John Bosnoian, Madison, MS, 1973 Plymouth Cuda 340

I have a ’73 ‘Cuda 340 with a 727 trans. and 3:55 gearsthat I did verify Before I rebuilt my transmission I was turning 3500RPM at55MPH. I did a full rebuild with new clutches seals etc., and a new TCIbreakaway converter. I am still running 3500 RPM at 55 mph. This is toohigh according to many rpm calculators. Is there any way that the finalgear could have been changed from 1:1 to 1.25:1? I have called many transshops, but no one is aware of any way to change the final ratio. Please giveme some help on this! How about the valve body, could it have been modifiedsomehow? The transmission appeared to have been worked on before but I can’tfind the person that did the work. Thanks, John


John, it’s one to one in 3rd gear. Take that to the bank.

There are really only a few possibilities, assuming the trans isn’tslipping. In order of likelihood:

> > Gears are really steeper the 3.55:1. I know you said you verified. This isstill #1 in my book. I suspect 4.56:1 or so.

> > Wrong speedo pinion is installed, or speedo cal is way off, and you arereally going faster than 55.

> > Tach is inaccurate

> > Super-small diameter tires (they’d need to be REALLY small).

> > Converter is a little 9″ race model or is defective.


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