Re: [AMC-list] speedo gears

[Ken Ames <ameskg@xxxxxxxxx>]

But it is almost 5.5%. Of the 5 vehicles I have on the road, only 1 is out by
more than 1 or 2% and that one is off because the tires are undersize.


Ken 

Quoting Frank Swygert <farna@xxxxxxx>:

> 
> HA! Good try! The fact is that the speedos just aren't that accurate, so you
> can get by with a little fudging on the speedo gears. Go to www.4lo.com and
> use the gear ratio and speedo check calcs. They don't have anything that uses
> the exact ratio for the speedo drive, but you can tell how little a few
> tenths of a gear affect speed. Old mechanical speedos are only accurate
> within +3-5%, so if you're off 3-5% on the gear drive it doesn't matter
> much... or maybe that's one reason they are no better than +3-5%...
> 
> Anyway, you can look at the speedo drive gear as a pinion gear and the driven
> gear as a ring gear and work out the ratio. For example, 18/7 = 2.57:1; 19/7
> = 2.71:1. Really only 0.10 difference, which isn't much (about 20 rpm on the
> tires). 
> 
> ------------
> From: das24rules@xxxxxxxxx
>  
> ok, lets see if we can stump frank, or tom, or anyone else who knows the
> rambler goodies well. my speedo gear in the original NONE o/d trans was 16
> teeth. looked like a black, or really dark red fiber nylon or something.
> speedo gear for my o/d trans is the natural nylon color. i THINK it had 16
> teeth on it also. but the gear ratios are different for o/d and none o/d
> cars
> i thought. i am currently looking in the tsm at the speedo gear info
> section.
> none listed for 3.77 gear with 16 teeth. no color of red, but there is a
> black, and it has 14 teeth. 4.10 gear has 16 or 17 teeth, for the same tire
> size. i dont get the difference, but ok. o/d with 4.10 is also 16 and 17
> listed. those are with 15x6.50 tire size, 781 rev per mile. with 15x6.70 747
> rev per mile tires, still lists 14 teeth for 3.77 gears. 15 and 16 gears for
> 4.10 axle, o/d or not. so, this CONFUSES me. none of it makes sense to me. i
> would think different tire size, different speedo gear, different rear gear,
> different speedo gear. then sometimes, nothing changes but the speedo gear.
> i
> am trying to figure out what i need to do to make my speedo as close as
> possible. i dont THINK it should be off any from what it was before if the
> driven gear is the same on the o/d, and it shows that it is same as none
> o/d.
> i hope i confused someone as bad as i am... if both gears i have are the
> same,
> i will run the gear that goes to this trans, as my original one was looking
> rather worn. guess ill just have to see how bad its off, and take note.
> anyone know how to locate new gears if i need one??
> 
> -- 
> Frank Swygert
> Publisher, "American Motors Cars" 
> Magazine (AMC)
> For all AMC enthusiasts
> http://farna.home.att.net/AMC.html
> (free download available!)
> 
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