3.73 speedometer gear
 

I put this under an existing thread and it didn't show on new posts so I am making this new thread.
I have a 3.73 rear gear in my WI SSP and the speedometer was way off when I drove it home. I was going to put a 2.73 in it but after reading the forum on which gears guys are running, I thought I may just leave the 3.73 in the AOD but the top speedometer gear is a 23 tooth and is not enough to correct the actual speed. There was a 21 tooth in it but some teeth were worn off which accounted for the needle wondering. What did you guys do to get the speedometer close to accurate? I read that the trans drive gear in the 93s had 8 teeth and on the chart it would need the max of 23 tooth gear on the speedometer end and it would still not be enough to make the speedometer accurate. They also said the nylon gears only last a short time and then it may break some teeth off like the one I have now. The other choice they gave was to change the trans gear from 8 to 7 or 6 but that is a big job. Any help on this would be appreciated or will I have to just live with it. Thanks.

Sounds like you already got some good advice. You can either change the trans and speedo gears (PITA), replace the 23 tooth gear, or put the original gear ratio back in.

http://mustangpartstech.com/SpeedometerGears.html

http://www.steeda.com/products/speed...tion_gears.php

Now I just heard about this, no actual experience. I guess that there is a small box with gears in it that you can attach between the trans and speedo to correct it as I have not found the proper drive/driven gears for the AOD/3.73 combo. Sure, they've got the combo for the T-5, but not for the AOD as I've seen.

the nylon/plastic gears are very durable, unless you are drag racing the car. For normal driving they will hold up very well. You should be able to get the correct tooth speedo gear at numerous vendors. Summit, FMR, 5.0 Resto, etc.

I put 3.55 gears in on of my AOD cars a few years ago and it took all of about ten minutes to change out the speedo cable gear and it was dead on.

3.73 may be different, not sure.

Jim,
All the charts I have seen show the 23 tooth gear is for the 3.55 but since the gear does not go beyond 23 teeth, the 3.73 and 4.10 will be off. I did put in the 23 gear and it did bring the actual speed closer but I haven't checked the accuracy as yet. I left the 3.73 in.

Toshi,
I haven't hear of the box adaptor so if anyone finds out about it, I would be interested. Thanks for the input.

Ford doesn't make a 23T (speedometer driven) gear for the T5 or AOD transmission. They go as hgh as 21T. There are 23T gears available but the teeth do have the correct pitch to mate well with the speedometer drive gear on the output shaft. The teeth are also thin, since there are so many of them on the gear. So what you have there is a combination for wearing out the gear and circulating plastic bits inside your transmission. Not a very desirable situation.

With a T5 you could change the 8T drive gear to 7T or 6T, as the drive gear is clipped onto the output shaft, but with an AOD you would have to tear the transmision down completely, as the drive gear is machined into the output shaft. And there is only 8T and 7T AOD output shafts available, no 6T.

You could get a speedometer repair shop to install a "gear reducer" in the speedometer cable. That's what stadair is talking about.

I new there was a cutoff on the gear size. I was thinking it was 3.73. With the 23 tooth gear you will probably be about 2.5 miles and hour off .

I had a '92 LX AOD car with 4.10 gears. The speedometer gear the shop put in was chewed apart within a few months. I actually ended up putting in a red standard gear which is for standard 3.73's and it was very close to accurate...not sure on tooth count. (Already had it laying in my garage from a previous car.) So I would imagine you could do the same, and since you have 3.73's you should be very close as well.

Red gear (manual trans) is 21T. If that was very close to accurate with 4.10 and an 8T AOD (late '89-'93), the tires must have been huge....enough to bring the final drive ratio way back down.

Drive Gear x Rear Gear x Tire RPM / 1000 = Driven Gear

Drive Gears
6T = Black = E3ZZ-17285-B (T-5 only)
7T = Yellow = E3ZZ-17285-A (T-5 only)
8T = Green = F0ZZ-17285-A (T-5 only)

Driven Gears
16T = Wine = C0DZ-17271-A (T-5) or Blue = D0AZ-17271-A (AOD) (discontinued)
17T = White = C3DZ-17271-C (T-5) or Green = C7SZ-17271-A (AOD)
18T = Yellow = C0DD-17271-B (T-5) or Gray = C7SZ-17271-B (AOD) (discontinued)
19T = Pink = CODZ-17271-B (T-5) or Tan = C7VY-17271-A (AOD)
20T = Black = C1DZ-17271-A (T-5) or Orange = C8SZ-17271-B (AOD)
21T = Red = C4OZ-17271-A (T-5) or Purple = D0OZ-17271-B (AOD)

excellent help by posting the part numbers !! appreciate that for future reference. :2thumbs: