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 Posted: 09-04-2006 10:31 pm
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upstate mike
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Joined: 09-27-2005
Location: New York USA
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Hi,

   the more I drive my 4 speed 74 JH the better the tach seems to work. The previous owner didn't put alot of miles on it for the years I have his service records for. Anyway I'm wondering how accurate my tach is reading 3000 rpm at 60 mph in 4th gear . Thanks in advance,

 

                                       Mike K

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 Posted: 09-05-2006 06:05 pm
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edward_davis
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Joined: 07-06-2005
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Mike, if you have the stock 185/70HR13 tires, the circumference of the tire should be about 6 feet.  At 60 mph, you're going ~90 feet per second, which works out to about 900 rpm for the wheels.  With the stock axle ratio of 3.727:1 and the 1:1 top gear, the engine should be going about 3350 rpm at 60 mph.  The stock JH tach often has difficulty with rpms in the midrange, but ~300 rpm is good for 30 year old electronics.

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 Posted: 09-10-2006 10:00 pm
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upstate mike
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Thanks for the info,

                       Mike K

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