AOD Speedometer Drive Gear Applications

[Tiggie]

It always bothered me that my '82 LTD Speedo was incorrect after a tranny swap. It was slow, indicating that went from a 8-T drive gear to a 7-T. It was said that an 8-T drive gear was very unlikely in a 1982.

The saying goes that most 1989 and prior AOD's got 7-T drive gears, while 1990+ got 8-T. That saying is now thought to be false based on what I have uncovered. It depends on model year, tire size, whether it's a Ford/Merc or a Lincoln, and even a Police difference sometimes. These are listed only for AOD's.

Taking a look at the 1980-1989 Master Parts Catalog, I found the following information:
1980

• 2.73 = 8
• 3.08 = 8

1981

• 2.73 = 8
• 3.08 = 8 unless P205/75-R14 Tires (7)

1982

• 2.73 = 8
• 3.08 = 8
• 3.42 = 7

1983

• 2.73 = 8
• 3.08 = 7 Ford/Merc
• 3.08 = 8 Lincoln
• 3.27 = 7 unless P205/75-R15 Tires (8)
• 3.42 = 7 Ford/Merc
• 3.42 = 8 Lincoln
• 3.55 = 7

1984

• 2.73 = 8
• 3.08 = 7 Ford/Merc (unless 225/75-R14 Tires)
• 3.08 = 8 Lincoln
• 3.27 = 8
• 3.55 = 7

1985

• 2.73 = 8
• 3.08 = 7
• 3.27 = 7
• 3.55 = 7

1986

• 2.73 = 8
• 3.08 = 7
• 3.27 = 8
• 3.55 = (not listed)

1987

• 2.73 = 8
• 3.08 = 7 or 8
• 3.27 = 7 or 8
• 3.55 = 7

1988

• 2.73 = 8
• 3.08 = 7 or 8
• 3.27 = 7
• 3.55 = 7

1989

• 2.73 = 8
• 3.08 = 7 except Police (8)
• 3.27 = 7 except Police (8)
• 3.55 = 7

It's worth noting that the catalog list different things for the Mustang/T-Bird/Baby LTD/Mark VII applications, which is probably where most of us got the idea about the 1989 7-T/1990 8-T.

Thoughts or comments? This would prove my theory that my '82 with 3.08 gears originally had a 8-T drive gear.

If anyone wants to crawl under their car and check, the 7-T is supposed to be yellow and the 8-T is supposed to be neutral. I am going to check my '88 at the next oil change.

[marquisman]

i know the 88 with the 3.08 has a green gear.

[1987cp]

i know the 88 with the 3.08 has a green gear.

As in, 16t driven gear? Interesting. I found it odd that my '87 CP with 3.27 gears wanted a 16t driven gear after no changes other than installing an aftermarket speedo and 28" rear tires. My '87 P72, on the other hand, came to me with a 16t driven gear that was presumably original from when it had 2.73 gears, and with 3.27 gears and 27" tires it was happy when I put in the 18t driven gear from the CP.

I don't remember for sure what driven gear I removed from my '81 with 3.08 gears and an AOD, but I calculated that it'd want a 21t driven gear after swapping to a C4, and SFAIK it's reading about spot-on. Don't know for sure what tires that car came with, but one would assume 14" since the only options are vinyl, A/C, wheelwell and rocker trim, and center front speaker.

[Tiggie]

I'm working on a speedo driven gear chart that's a little easier to understand. My '82 w/3.08 and '87 with 3.27 both had gray 18-T driven gears. I have not checked my '88 yet but I'm going to next oil change. I installed a PI speedo and it's reading 4mph slow now.

C4's and FMX's also had different drive gears depending on rear axle ratio - 8T and 9T.

I'm working on a generalized list that will be correct for our cars of driven gears so we'll know what's really correct for OEM and what we need to do to fix it before ordering 3 extra speedo gears.

[Tiggie]

I'm compiled this chart based on the catalog. It is just for AOD cars. I have a feeling there are some more exceptions, and I did generalize some applications.



I know I've heard of 3.55 cars having orange or purple gears. I guess it would be needed with an 8T drive gear.

1987cp - I'm guessing you C4 has an 9T drive gear which was available on them, thus the need for a 21T driven gear with just 3.08 gears.

Also - two errors in the first drive gear chart. 1983 and 1985 with 3.27 should 8T. Could a moderator change that for me?

I'd like input on whether everyone's car matches this list or not.

My input:
1982: 3.08 with 18T Driven - No Match
1987: 3.27 with 18T Driven - Match
1988: 3.27 TBA

[88grandmarq]

Every AOD that I have taken apart or seen pictures of taken apart, the drive gear is machined into the metal output shaft. which requires taking the transmission completely apart to change the output shaft.

some of the C3/C4 transmissions had plastic gears on the output shaft, However, I still think the output shaft had to be removed from the transmission to replace the gear.

[88grandmarq]

I'm compiled this chart based on the catalog. It is just for AOD cars. I have a feeling there are some more exceptions, and I did generalize some applications.



I know I've heard of 3.55 cars having orange or purple gears. I guess it would be needed with an 8T drive gear.

1987cp - I'm guessing you C4 has an 9T drive gear which was available on them, thus the need for a 21T driven gear with just 3.08 gears.

Also - two errors in the first drive gear chart. 1983 and 1985 with 3.27 should 8T. Could a moderator change that for me?

I'd like input on whether everyone's car matches this list or not.

My input:
1982: 3.08 with 18T Driven - No Match
1987: 3.27 with 18T Driven - Match
1988: 3.27 TBA

your list seems fairly accurate. Brian's town car had a factory 3.27 gear and a 18T gray gear. pretty much every K-code rear car I have found had a tan 19T gear.

[1987cp]

Yes, 9t driven gear sounds right. Easy to count drive gears with the tailshaft off. IIRC I also calculated 21t based on my '79 having a 16t driven gear with its 2.26:1 rear.

[gadget73]

Mine had a tan originally with the 3.55 , and it was way the hell off. I believe I fixed it with an orange gear. At some point when I changed transmissions it wanted the purple one, and now I'm back to an orange gear. Gears have always been a 3.55.

[1987cp]

I found it odd that my '87 CP with 3.27 gears wanted a 16t driven gear after no changes other than installing an aftermarket speedo and 28" rear tires.

Scratch this ... I was just pondering the fact that this car got a replacement transmission in '04, so it's possible it now has a different speedo drive-gear tooth count. That could possibly account for wanting a 16t driven gear when an 18 came stock.

[Mercracer]

Every AOD that I have taken apart or seen pictures of taken apart, the drive gear is machined into the metal output shaft. which requires taking the transmission completely apart to change the output shaft.

some of the C3/C4 transmissions had plastic gears on the output shaft, However, I still think the output shaft had to be removed from the transmission to replace the gear.

It is a fact that the AOD drive gear is machined into the output shaft. I have never seen a C3,C4,C5,C6 with a plastic gear. I do not believe that they exist. Standard transmissions have a removable gear on the output shaft.

If anyone wants to crawl under their car and check, the 7-T is supposed to be yellow and the 8-T is supposed to be neutral. I am going to check my '88 at the next oil change.

That may be true for a T5, but on an AOD, etc.. it is part of the output shaft and not colored....

[Tiggie]

That may be true for a T5, but on an AOD, etc.. it is part of the output shaft and not colored....

There was an note in the catalog about the drive gear being a part of the output shaft. I got the drive gear colors from some online digging which was most likely for T5 apps.

I guess the only way to count drive gear teeth would be to put an ink mark on one tooth and rotate the output shaft until that tooth comes back around on an AOD. I'll give it a shot when I change my oil next week. Might be a little hard to see in there with the tranny in the car.

[88grandmarq]

you can count the teeth, but you will need to remove the extension housing to do it.

[Tiggie]

Noticed another error - the blue 16T driven gear is PN D0AZ-A not D0AZ-B.