its on the drivers side of the transmission near the rear part of it. 1 bolt holds it in. theres a little c-clip that holds the gear itself to the VSS sensor, that just pops off and u can swap em
I did a search on corral and came up with this reply:
Its not hard to change the Speedo gear on the outout shaft. All you do is undo the rear case, and drain the tranny fluid out, then take it off and its right there, should be black, if you have 3.08's. You get the white one from any ford dealership. Just tell them you need a White 6 tooth speedo gear for the output shaft on a T-5. Or you can look in the FMS Catalog in the Rear End section. When done, clean the case as good as you can, then black silicon the case, and connect it and put the black speedo gear in place the connects to the harness, and bada bing bada boom yo done.
I hope to attempt the swap this coming Sunday afternoon or Monday.
Update:
I finally got around to attempting to swap out the DRIVE gear on my tranny. First of all, I would like to say that this was NOT as easy as described in the reply I posted from the Corral. I had to take the tranny out anyway because of an oil leak which I thought was from the RMS-more on that later. After removing the tranny I removed approx. 8 bolts which held the rear case to the gearbox. I thought the case would then just slide off but it was hung up on the shifter shaft. Thankfully Mike (aka. Wazee) had sent me a link to the schematic of the Borg Warner T5. This proved invaluable as I know NOTHING about transmissions. Anyhow, there is a rollpin which secures the offset lever to the shifter shaft. I used a punch to drive the pin out which then allowed the rear case to come off.
It was pretty straight forward removing the speedo drive gear and then replacing it with the 6 tooth gear. After cleaning up the mating surfaces up I used some Permatex Ultra High temp black silicone to seal it up. Please note that the offset lever has a spring with ball bearing that must be put in place in order for the rear case to go back on because you WON'T be able to do it after the fact which I learned the hard way!
Overall impression is to save yourself ALOT of trouble and get the SpeedCal. If I didn't need to drop the tranny anyway I would have went this route.
The good news is that my RMS looks OK. Turns out the oil leak was coming from the flywheel bolts which I neglected to use thread sealer on. Chalk another lesson I learned the hard way!
wish i had seen this last week before you tried it, i could have warned you about it, good thing is now that if you change ratios again all you should have to change is the driven gear.
I would not have done it either, if i hadn't already pulled the tranny when the driveshaft let loose...