AOD speedometer drive gear question
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Elder User
Joined: Jan 2014
Posts: 531
Likes: 8
From: Bakersfield, CA
AOD speedometer drive gear question
I have a rebuilt AOD transmission. I am trying to identify what speedometer drive gear the company put in it. They say they just count the teeth and replace it with the same count it came with. So they don't know. I tried to identify the gear by color BLACK/six teeth YELLOW/7 teeth GREEN/8 teeth. Mine looked more BLACK than anything but, based on the charts YELLOW and GREEN seemed to be more prevalent. The World Wide Web also said the aftermarket doesn't really conform to the manufacturers colors. Ideally I would like to choose a speedometer cable gear that matches my drive gear. More importantly I need to be sure if my cable gear and my drive gear are not matched it will only mess up my speedo reading and not chew up my gears. What say you?
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
The speedo drive gear on the AOD/AOD-E/4R70W transmissions is machined into the output shaft and is not removable or swappable. Color doesn't really figure into identifying the drive gear. The driven gear that goes on your cable is what should be color coded. Some driven gear tooth counts won't play nice with some drive gear tooth counts, so it is important to know what you've got to start with.
There are 7,8, and 9 tooth variants of the output shafts. The 9 tooth is fairly rare as very few combinations cannot be dialed in with a 7 or 8 tooth shaft. The teeth are spiral cut around the shaft and are difficult to count with the tail shaft housing installed. Counting the teeth is, however, the only way to figure out exactly what you have. Removing the housing is just a matter of unbolting it and sliding it off. Start at either end of the gear, locate the root or beginning of one tooth, and mark it. Count the roots of the teeth around the shaft from that point to get a tooth count.
There are 7,8, and 9 tooth variants of the output shafts. The 9 tooth is fairly rare as very few combinations cannot be dialed in with a 7 or 8 tooth shaft. The teeth are spiral cut around the shaft and are difficult to count with the tail shaft housing installed. Counting the teeth is, however, the only way to figure out exactly what you have. Removing the housing is just a matter of unbolting it and sliding it off. Start at either end of the gear, locate the root or beginning of one tooth, and mark it. Count the roots of the teeth around the shaft from that point to get a tooth count.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 785
From: Simi Valley, CA
Here's a pic from the text section of the 1980/89 Ford Light Truck Parts Catalog that shows AOT (AOD) parts.
Look at basic part number 7060 .. which is the output shaft.
I have another pic I can post with additional proof of the location of the AOD DRIVE gear.
Senior User
Joined: Nov 2007
Posts: 494
Likes: 1
From: Guelph
I used an AOD in my truck and a rear end from a Explorer. Dont no the gear ratio. I use the original speedo cable and modified the speed sensor on the trans to except the cable and its only about 4 MPH off.
Cargo Master
Joined: Sep 2004
Posts: 2,757
Likes: 138
From: Alberta Canada
My AOD is from a 1990 Crown Vic; (sender on left in picture). It had a stock green gear. I tried unsuccessfully to use the original speedometer and change the gear, and stock speedo meter face, but with no luck. I ended up using Autometer electronic speedo and pulsed output sender(on right in picture) and transposed the green gear to it. I am still registering high readings, so this weekend I will be pulling the instrument cluster(yet again) to see if I can solve the issue.
From what I have rerad, you should be able to use a different geared drive calculed by tire size and number of rotations; I'll have to dig into my research as to where I found a chart.
Tom
More Turbo
Joined: Aug 2003
Posts: 533
Likes: 33
From: Foxworth, Ms.
Are you using a mechanical or electric speedo? I have a mechanical with AOD/Explorer axle combo. Mid Fifty offers 4 possible gears to install on the end of the speedo cable. I bought all 4 and used the one that was closest to GPS speed. I'm sure there is math to figure this another way but this worked for me!! Good luck, Steve
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Elder User
Joined: Jan 2014
Posts: 531
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From: Bakersfield, CA
The AOD DRIVE gear could have 7 or 8 teeth, but it cannot be replaced by itself, as it's made as part of the output shaft.
Here's a pic from the text section of the 1980/89 Ford Light Truck Parts Catalog that shows AOT (AOD) parts.
Look at basic part number 7060 .. which is the output shaft.
I have another pic I can post with additional proof of the location of the AOD DRIVE gear.
Here's a pic from the text section of the 1980/89 Ford Light Truck Parts Catalog that shows AOT (AOD) parts.
Look at basic part number 7060 .. which is the output shaft.
I have another pic I can post with additional proof of the location of the AOD DRIVE gear.
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Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
I sure don't need proof........but hopefully a picture will be the only way I see what's inside my transmission. Maybe I could print it out and take it by the transmission place. I started off with a lot of misinformation on this subject. Thanks to all for getting me back on track!
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Elder User
Joined: Jan 2014
Posts: 531
Likes: 8
From: Bakersfield, CA
So as I understand it the Drive gear in the transmission is metal and there to stay. The DRIVEN GEAR is plastic or polymer and can be changed. What happens when the metal gear eats the plastic gear? Where does the plastic end up? Any possibility of transmission failure as a result?
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
Here's the DRIVEN gear pages from the 1973/79 Ford car catalog that shows the types (upper pic); colors and tooth counts (lower pic). C0DD-17271-A was replaced by C0DZ-17271-A
Cargo Master
Joined: Jun 2001
Posts: 2,571
Likes: 22
From: Oxford, Indiana
As I mentioned in my first post, there are only a few tooth counts that aren't compatible and wear quickly. In those situations, the plastic ends up eventually getting washed to the pan and will likely be caught in the filter. The amount and size of the particles is inconsequential and it is doubtful that this could ever cause transmission failure. The biggest contributors to failure in an AOD in normal use are incorrect TV pressure and heat. If you set the TV pressure right and keep it cool, it'll last indefinitely regardless of a little plastic dust.
With that being said, if you choose compatible tooth counts, the plastic driven gear should last a couple hundred thousand miles with little if any detectable wear.
With that being said, if you choose compatible tooth counts, the plastic driven gear should last a couple hundred thousand miles with little if any detectable wear.
Cargo Master
Joined: Sep 2004
Posts: 2,757
Likes: 138
From: Alberta Canada
Is this any good to you?
This is not the vendor I was thinking of but it may be worth a look:
Speedometer Gear Calculator and Charts - TCI® Auto
Tom
Speedometer Gear Calculator and Charts - TCI® Auto
Tom
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