Thanks for the replies on this thread.
I dug into this a little more, and went to the 1956 Parts list (PUblication
1050, ed2). I now realize that the 140 mph spedometer (7H1751), rated in the
catalogue at 1180 rev/minute, equates with a special axle ratio of 3.6,
against the 120 mph speedometer (3H3061) which is rated at 1325 rev/min for
the stock 4.125 stock axle ratio. The conversions are not identical (1180/1325
= 0.891:1 and 3.6/4.125= 0.8727), but I get the general idea.
I know understand that some later BN** pumpkins are rated at 3.90 and hear
some BN2 owners have gone to this for longer legs without perceivably
sacrificing acceleration. This has been recommended by atleast one M owner in
prior correspondence. Our engine is really hoofy (lightened flywheel, 0.60"
oversized rings from PO, headers, etc., so I wouldn't mind some longer gears
in 2nd and 3rd gear. The majority of our drving is on unengineered winding New
England secondary roads, where overdrive is seldom needed. With just a little
more speed in 4th we could do without it almost all the time.
If I were to make the conversion to 3.9, this would reduce the speedometer
error by roughly half (3.9/4.125=0.9454). If we do this, can the instrument
services adjust the other half without changing the spedometer gears?
Any thoughts on the 3.90 conversion or on the range of adjustability of the
speedometer mechanism would be appreciated.
Also, are 3.6 rears available for the BN2 pumpkin?
One of the responses to my last inquiry mentioned a BJ8 conversion to 3.54"1
rear. Is that something that can be done with a BN2 axle housing?
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