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Topic: what speedo gear options are there? (Read 1993 times) previous topic - next topic

what speedo gear options are there?

I have an 87 XR-7 with AOD and 3.73s. stock was 2.73:1
I'm running the pony rims with 245/50-16 tires so my rolling cirspoogeference should be at or near stock(235/60-15). I changed the speedo gear to the one the dealer told me was as close as he could get since AOD cars never came with steep gears. The gear was purple (21 tooth, I think) instead of the grey one(18 tooth?). So my question is, is there another gear that I am unaware of that will correct my speedo? It reads fast by 15-20%. Will a speedo gear from a T-5 fit? I know the Turbo-coupe came with 3.73s so that would solve my problem if they fit. If not, any other suggestions?

Re: what speedo gear options are there?

Reply #1
Here's a link from the old site that has a calcilator to figure it out:

http://tciauto.com/tech_info/speedo_gears.htm

If you scroll down there is a list of AOD gears.

I recently discovered that the AOD speedo drive gear is machined into the output shaft. The AOD will have either a 7 or an 8 tooth drive gear and there is no way to tell without removing the tail shaft housing. If you have a 7 tooth drive gear you need a 20 tooth driven gear, if it's an 8 toother you'll need the 23 tooth gear.

For me, my choices were between a 19 and 21 tooth gear for 3.55's. At $13 each I decided to just order both gears rather than pull the tail housing... I ordered my gears from this site (free shipping):

http://www.transmissioncenter.net/AOD.htm
[SIGPIC][/SIGPIC]
86 5.0 Turbocoupe (Katrina), 87 5.0 Sport (Rita)

Re: what speedo gear options are there?

Reply #2
Thanks Dogcharmer,
                I'll definitely look into it. It's been too long that I've been guessing.

Re: what speedo gear options are there?

Reply #3
Yup you have the 8 tooth output shaft. I was lucky, my Super Coupe AOD has the 7 tooth output shaft and the 21 is right on. There is a 23 tooth gear available, but its a Chrysler[Jeep I believe] rather than a Ford part. Just check with one of the late model Mustang parts supplier(Mustangs Unlimited comes to mind).

Re: what speedo gear options are there?

Reply #4
I think I am running the 21 tooth with 3.73's and it is only ~3mph low at 70