Speedometer gears
- Thread starter dan and the 302
- Start date
krahkin
Member
There should be a 19-tooth gear in your stock configuration. Why not just get a SpeedCal? That way when you change tires, gears, etc. you can just flip a dip switch and have stock accuracy. Yes, I run one. 
mustangmax
Founding Member
Ive got the same problem. I checked out the website mentioned, but the best fit isnt in the category that says T-5 only. When I had my gears set up, they swapped the tranny gear but it was way off. I complained and was told it was because of my tire/rim combo. Ive changed to a 255/40/17 which is closer to the right diameter and its still way off. I know some t-5's are supposed to have a different # of drive gears... Any ideas?
PNY PWR
New Member
the chart doesn't have the 23 tooth listed which is what I've found to need for mine from other sources. I think it was to change the drive to a 7 and the other to a 23.
I'm not sure what drive gear mine has, I know it changed from 89 to 90. 90-93 you have to change the drive gear at a certain ratio.
I'm not sure what drive gear mine has, I know it changed from 89 to 90. 90-93 you have to change the drive gear at a certain ratio.
Tire Circumference = Tire Section Width / 25.4 * (Tire Aspect Ratio / 100) * 2 + Wheel Diameter * Pi
Tire RPM = 63360 / Tire Circumference
Driven Gear = Drive Gear * Rear Gear * Tire RPM / 1000
Available Drive Gears: 6T, 7T, 8T
Available Driven Gears: 16T, 17T, 18T, 19T, 20T, 21T, 23T (not Ford)
'83-mid '89 T-5: 7T drive gear
mid '89-'95 T-5: 8T drive gear
If the transmission in this '95 GT is a T-5, the drive gear is 8T. Any gear ratio lower (higher numerically) than 3.55:1 there is no driven gear available for. (And even then, 23T driven gears aren't Ford gears, they're Chrysler gears and they're crap. The teeth are thin, and they will wear out quickly. There'll be plastic bits floating in your transmission and the speedometer will be bouncing all over the place. Expect to change 23T driven gears often.) You must switch the drive gear to 7T or, preferably, 6T and get the appropraite driven gear.
If the transmission in this '95 GT is an AODE, you have two problems. First problem is that the drive gear is machined to the output shaft. That means the whole shaft has to be changed. That means a transmission teardown and rebuild. The second problem is that the AODE is electronically controlled and it WILL NOT live a long and properous life with anything lower than 3.55:1 gears. Read THIS article.
EDIT: Corrected typos.
Tire RPM = 63360 / Tire Circumference
Driven Gear = Drive Gear * Rear Gear * Tire RPM / 1000
Available Drive Gears: 6T, 7T, 8T
Available Driven Gears: 16T, 17T, 18T, 19T, 20T, 21T, 23T (not Ford)
'83-mid '89 T-5: 7T drive gear
mid '89-'95 T-5: 8T drive gear
If the transmission in this '95 GT is a T-5, the drive gear is 8T. Any gear ratio lower (higher numerically) than 3.55:1 there is no driven gear available for. (And even then, 23T driven gears aren't Ford gears, they're Chrysler gears and they're crap. The teeth are thin, and they will wear out quickly. There'll be plastic bits floating in your transmission and the speedometer will be bouncing all over the place. Expect to change 23T driven gears often.) You must switch the drive gear to 7T or, preferably, 6T and get the appropraite driven gear.
If the transmission in this '95 GT is an AODE, you have two problems. First problem is that the drive gear is machined to the output shaft. That means the whole shaft has to be changed. That means a transmission teardown and rebuild. The second problem is that the AODE is electronically controlled and it WILL NOT live a long and properous life with anything lower than 3.55:1 gears. Read THIS article.
EDIT: Corrected typos.
Qwk88LX
Member
When I put my speedo gear in (23T) I examined it & it didn't seem like the teeth on it were any thinner than the stock 19T one. Plus the old one which had probably been on the car since 88' didn't look worn out. What do you mean by "often"? I haven't had any problems with mine bouncing neither..FoxChasis said:
Ford only makes driven gears with up to 21 teeth. The only 23T drive gear that I know of that'll fit this (T-5) application is a Chrylser gear (Jeep part # j3167393).
Since there are (obviously) more teeth on a 23T gear than any others, the teeth must be made thinner to all fit on the gear and still be able to mesh with the drive gear.
Not all 23T driven gears fail but it IS a common occurence. Be prepared for that possibility. It may take 1000 miles. It maky take 5000 miles. It may take 10,000 miles. It may never happen.
Since there are (obviously) more teeth on a 23T gear than any others, the teeth must be made thinner to all fit on the gear and still be able to mesh with the drive gear.
Not all 23T driven gears fail but it IS a common occurence. Be prepared for that possibility. It may take 1000 miles. It maky take 5000 miles. It may take 10,000 miles. It may never happen.
krahkin said:There should be a 19-tooth gear in your stock configuration. Why not just get a SpeedCal? That way when you change tires, gears, etc. you can just flip a dip switch and have stock accuracy. Yes, I run one.
where'd u get a speedcal? i'd like one as well, as i've changed the tire size and have 3.73's going in fairly soon. thanks.
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