Speedometer Gear - Ford Mustang Forum
 
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post #1 of 3 (permalink) Old 05-16-2018 Thread Starter
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Speedometer Gear

Hey all,

I have a question regarding speedometer gears. I am currently running a 275/40/17 with 4.10 gears and an AOD transmission. According to the charts, I am in need of a 25.8 tooth gear to make my speedo read close to correctly.

I am hosed, as the shaft mounted gear inside my 1991 AOD is an 8 tooth gear. Can't change that without a complete rebuild or at least a total tear down. Apparently, the gear is machined into the input shaft.

All of the usual places carry up to a 23 tooth gear. Has anyone heard of a higher tooth count gear?

If I really need to, I could change out the rear gears to a 3.73 and be close. Those gears ask for a 23.5 tooth drive gear in the transmission. I guess that would be the closest, as I currently have 23 tooth.

Thanks for any help or ideas.


1991 Mustang LX 5.0 Convertible. 302, GT40 Heads, GT40 Intake, 1.6 Harland Sharp Roller Rockers, Accufab 75mm TB, BBK 75mm MAF, BBK CAI, 24# injectors, F303, MAC shorty headers, BBK off road H pipe, Flowmaster 40 series, Ford 4.10 gears, SR Perf Upper and Lower control arms, SR Perf Full Length Subframes, Ford Racing "B" Springs, Eibach Pro-Dampers, Smog deleted, rebuilt AOD with 4r70w gears
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post #2 of 3 (permalink) Old 05-16-2018
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Quote:
Originally Posted by 91convert50 View Post
Hey all,

I have a question regarding speedometer gears. I am currently running a 275/40/17 with 4.10 gears and an AOD transmission. According to the charts, I am in need of a 25.8 tooth gear to make my speedo read close to correctly.

I am hosed, as the shaft mounted gear inside my 1991 AOD is an 8 tooth gear. Can't change that without a complete rebuild or at least a total tear down. Apparently, the gear is machined into the input shaft.

All of the usual places carry up to a 23 tooth gear. Has anyone heard of a higher tooth count gear?

If I really need to, I could change out the rear gears to a 3.73 and be close. Those gears ask for a 23.5 tooth drive gear in the transmission. I guess that would be the closest, as I currently have 23 tooth.

Thanks for any help or ideas.
Even the white Speedo gear for the 3.73’s isn’t great. It’s actually a Jeep part and it only pseudo mates up. After awhile the teeth will get chewed up and the speedo will be off.

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post #3 of 3 (permalink) Old 05-16-2018
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I think the gear for the 3.27 is the numerical highest that will actually mesh correct without changing the trans gear as well.
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