Jim,
In order to calculate what new speedo gear to select, you
need to baseline where you are starting from. You will need a watch with a
second hand and a freeway with mile markers. When you are going 60 mph it takes
60 seconds to travel 1 mile. Cruise at a steady speed that you think is 60 mph
and measure the time. Adjust your speed until you are getting 60 seconds
between mile markers and note the mph reading on your speedometer. Some states
are more accurate than others when planting mile markers, so an average of
several miles is best.
Next you need to remove the speedo gear from your
transmission and count the number of teeth on the gear. Consult your shop
manual. Then put it back.
The math is simple.
T = the number of teeth on your current speedo gear.
X = the number of teeth your speedo gear should be to be
accurate.
C = your current speedometer reading at 60 seconds per mile.
Plug the numbers into this equation:
C x T = 60 x X
Or
X = CxT
60
Example:
T = 18
C = 68
X = 68x18 = 20.4
60
X = 20 teeth
A higher tooth count will slow down your speedometer.
I am also looking for a speedo gear for my
1962 – 1965 727 Aluminum TF. I need a 21 tooth gear, P/N 2204360. These are different than the earlier cast
iron TF and the later 727s. Anybody have one or a source?
Dave Homstad
56 Dodge D500
-----Original
Message-----
From: Forward Look Mopar
Discussion List [mailto:L-FORWARDLOOK@xxxxxxxxxxxxx]On Behalf Of Jim Ruckdashel
Sent: Sunday, February 17, 2008
12:36 PM
To: L-FORWARDLOOK@xxxxxxxxxxxxx
Subject: [FWDLK] Speedometer gears
Hi List. I have a 58 Ply with the orginal
3.31 rear gear.(The car had a Powerflite and 318 engine from the
factory). I put in a 361engine and CI Torqueflite from a 59 Dod. I
have 15 inch Chrysler wire wheels and P215x78-15 tires on them. The
speedometer is fast--not sure how much tho. It can show 55-60 when driving
along with what I think is 45-50 mph traffic.I think there are
speedometer gears that can be changed to get it closer to right. So I have
a couple of questions.
What gear should I select; Up or down to
slow the speedometer down?
How would I calculate the correct gear
ratio?
Where could I find gears to choose from?
How hard are they to change out?
Any help will be appreciated.
Thank. Jim
Jim Ruckdashel
4241 Singing Post Lane
Roswell, GA 30075
770-992-9746
Jruckdashel@xxxxxxxx
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