Math puzzler

Unknown
Unknown
edited November -1 in HUDSON
Ok here's the question for you math whizzes.....

I switched my car over from a 3 speed no overdrive to a dual range hydro. I still have the same rear end (410)and tires......how much did this change my speedo??



The speedo is definately out but I have no idea how much now.

Comments

  • Unknown
    Unknown
    thanks Ken, so if my speedo is showing 60 mph x .66= 39.6 mph is my actual speed? If that is true its almost exactly a switch from mph to kph.



    I'm definately going to need a higher ratio rear end.
  • Unknown
    Unknown
    I also might explain why my transmission is shifting so fast. I'm barely moving and I'm in third gear and not much more it goes into 4th.
  • Unknown
    Unknown
    or is it 4.10divide by 60 times 3.07 divide by x=44.9 mph? ah, I forget all these formula things
  • [Deleted User]
    [Deleted User]
    Thanks Jim, now I have to sit down and solve x, that's just not right to do to a guy on a friday night.



    Harry
  • junkcarfann
    junkcarfann Expert Adviser
    A 4:10 ratio with an automatic is high RPM drag-racing territory. You need a 3:10 or something near it.



    Also, here is a calculator that might help:



    http://www.offroaders.com/info/tech-corner/reading/mph-rpm.htm
  • [Deleted User]
    [Deleted User]
    I'm glad someone came up with a calculator, I calculated x as .00476 and that didn't seem right to me.



    Harry
  • Ol racer
    Ol racer Senior Contributor
    The largest problem 4.10 is far too low for an Automatic and similar to driving down a highway in 2nd gear restricting top speed.



    The erroneous speedomer will become correct if you switch to the automatic rear end ratio, 3.07......
  • Park_W
    Park_W Senior Contributor
    All the above posts are assuming that the spiral gear on the Hydramatic tranny output shaft is the same pitch as the one in the original standard tranny, and that the original speedo pinion will mate up to it. But that isn't the case. What one CAN say, I think, is that if the original speedo pinion is replaced with the proper one for a 3.07 axle (SW # 418845, 18 teeth), the speedometer will be pretty close. And that's only true if the car is a '51 or later (not an earlier one where the speedo cable turned twice as fast at a given speed.
  • Unknown
    Unknown
    Park I had to change the cable as the one for the original stick tranny was a completely different connection than the one for the automatic.

    All I know is the engine is really screaming at 60 mph and I think I'm actually going 40mph. Also the tranny shifts so fast its in third by the time I get 30 feet.
  • Ol racer
    Ol racer Senior Contributor
    FYI

    I installed a Hydro into a stick OD geared Hudson way back in the late 50's and it was unbeatable light to light but had no highway speed....



    The first thing you need to do is change the rear gears, then secondly, correct the Speedo if necessary....
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