I have 3:73 gears, ive had them for awhile and i heard someone say that it you dont change your speedo gear that your mph will not only be off but so will your odometer. Is this true and how much is mine off by now?
Yes, that is correct. I changed my speedo gear and mine is still off a bit. My speedo reads about 5 MPH fast at 60, so it is about 8% off ( 5/60=.08333) So, if I drive 100 miles, my odometer says I drove about 108 miles.
You just need to do the calculations over the time period you have driven with the wrong gear to get an estimate. More than likely you are about 30-35% over on your miles vs the stock gears, for the time since you changed them.
is that gear u have to change on the cable end or is it the one on the output shaft of tranny...
recently swapped t5's and the output shaft gear looks exactly the same, and it would make sense that u have to change the outer gear, since u wouldnt have to pull the transmission to do so
You're over driving the odometer and the speedometer by the ratio of (new gear/old gear)
If your old gear was the stock 2.73s (well.. auto could get 3.27s, but assuming 2.73s):
(3.73)/(2.73) = 1.37
So, your speedometer and odometer will show 137% of what is actually being put on.
If your trip odometer shows an 137 miles, you will actually only put on 100. If the speedo shows 137mph, you're actually only doing 100mph.
To correct this, you have to change the gear that is on the end of the speedo cable, or the vehichle speed sensor (which is on the end of the speedo cable) that goes into the transmition.
Now, the gear that you need depends on what transmition you're running. But, for my TKO (from an AOD), I needed (I believe I have the right color) the RED gear (the different speedo gears are all color coded). Again, if memory serves me, there are a couple different gears that you might need to use based upon the number of teeth on the transmition's speedo gear (6,7 or 8 tooth I believe).
But, I'm almost 90% sure, for a 7 tooth drive TKO, w/ 3.73s, it was the RED gear that I used.