Re: [AMC-list] speedo gears

[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!)

_______________________________________________
AMC-list mailing list
AMC-list@xxxxxxxxxxxx
http://list.amc-list.com/listinfo.cgi/amc-list-amc-list.com