T98 Speedo Gear Combinations/Availability Questions
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Cargo Master
Joined: Aug 2015
Posts: 2,075
Likes: 101
From: Marana, Arizona
T98 Speedo Gear Combinations/Availability Questions
I have a formula to calculate speedo gears needed for a particular gear ratio and tire size.
My 1952 T9 has the same steel or iron DRIVE gear as my 1950 T98. It is part # 01-T-85-B6. I don't know how to count the teeth on this sucker but I'm thinking it has 6 based on the number.
The DRIVEN gear in the 1950 F6 T98 is part # 01-T-71-D21 and has 21 teeth.
The DRIVEN gear in the 1952 F3 T9 is part # 01-T-71-B19 and has 19 teeth. Both are steel or iron.
The formula I found:
# Drive Gear Teeth x Gear Ratio x Tire Rev/Mi Divided by 1000 = Driven Gear Teeth Needed.
So my 7.50-16 OR 235/85R-16 Tires are 637 Rev/Mi.
My Gear Ratio is 3.73
IF my DRIVE gear is 6 Teeth my DRIVEN gear calculates out to be 14 teeth.
FINALLY my question. Is there a 14 tooth gear and is it compatible with my 6 tooth metal gear or do I need an entirely different combination?
Are there more DRIVE gears available? And how many driven gears will work with each?
Once I find out what is available for gears I can plug in the numbers and figure it out.
My 1952 T9 has the same steel or iron DRIVE gear as my 1950 T98. It is part # 01-T-85-B6. I don't know how to count the teeth on this sucker but I'm thinking it has 6 based on the number.
The DRIVEN gear in the 1950 F6 T98 is part # 01-T-71-D21 and has 21 teeth.
The DRIVEN gear in the 1952 F3 T9 is part # 01-T-71-B19 and has 19 teeth. Both are steel or iron.
The formula I found:
# Drive Gear Teeth x Gear Ratio x Tire Rev/Mi Divided by 1000 = Driven Gear Teeth Needed.
So my 7.50-16 OR 235/85R-16 Tires are 637 Rev/Mi.
My Gear Ratio is 3.73
IF my DRIVE gear is 6 Teeth my DRIVEN gear calculates out to be 14 teeth.
FINALLY my question. Is there a 14 tooth gear and is it compatible with my 6 tooth metal gear or do I need an entirely different combination?
Are there more DRIVE gears available? And how many driven gears will work with each?
Once I find out what is available for gears I can plug in the numbers and figure it out.
Thread Starter
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Cargo Master
Joined: Aug 2015
Posts: 2,075
Likes: 101
From: Marana, Arizona
Thanks Ross.
If I can use an 8 tooth drive gear with a 19 tooth driven gear it calculates out.
Would those two gears work together or is it only in the combinations in your chart?
If I can use an 8 tooth drive gear with a 19 tooth driven gear it calculates out.
Would those two gears work together or is it only in the combinations in your chart?
Fleet Owner
Joined: Jul 2004
Posts: 27,296
Likes: 1,059
From: NM
I don't know, honestly. I bought a different drive gear and it about ruined my driven gear in 20 miles. I suspect only factory combinations work reliably. I also paid about $30 for the driven gear (NOS). For a hundred or so you can buy a "ratio adapter" that mounts in the cable for whatever conversion ratio you need.
Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4
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Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4
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Thread Starter
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Cargo Master
Joined: Aug 2015
Posts: 2,075
Likes: 101
From: Marana, Arizona
Yeah, I originally thought I'd be buying a ratio adapter. Just thought I might have gotten lucky being able to use stock gears.
I realize the driven gears usually have a limit of a couple teeth difference working with a specific drive gear.
Is there more to your chart? My 19 tooth driven is factory matched with a 6 tooth drive. I don't see that on your chart. If you see any combinations with the 19 and 8 it may work.
I realize the driven gears usually have a limit of a couple teeth difference working with a specific drive gear.
Is there more to your chart? My 19 tooth driven is factory matched with a 6 tooth drive. I don't see that on your chart. If you see any combinations with the 19 and 8 it may work.
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Cargo Master
Joined: Aug 2015
Posts: 2,075
Likes: 101
From: Marana, Arizona
I'm a newb. No CD unfortunately. I try to search before I bug you guys so I usually have at least some info before I ask.
Thanks!
Thanks!
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Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
My 1952 T9 has the same steel or iron DRIVE gear as my 1950 T98. It is part # 01-T-85-B6.
01T-17285-B 6T
The DRIVEN gear in the 1950 F6 T98 is part # 01-T-71-D21 and has 21 teeth.
01T-17271-D
The DRIVEN gear in the 1952 F3 T9 is part # 01-T-71-B19 and has 19 teeth.
01T-17271-B
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Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
01T DRIVE gears used with 01T DRIVEN gears.
I cannot find a combination of 01Y DRIVE gears with 01T DRIVEN gears.
Senior User
Joined: Aug 2018
Posts: 158
Likes: 1
This is a very common swap, I am surprised we have not heard of what anyone else has done. We are both in the same boat.
I have a 6/19 setup now, so going to the available 7/19 is half way of the correction...
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Cargo Master
Joined: Aug 2015
Posts: 2,075
Likes: 101
From: Marana, Arizona
Aaron, please post up whatever you end up doing for us other swap guys. I'll probably end up buying a conversion gear box. Just don't know when I'll get to that point. I'll be sure to post up my fix at that time.
Senior User
Joined: Aug 2018
Posts: 158
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Thus far highly considering the same thing, they make a 28% increase correction box. At speedo saying 44, and actually going 55 per GPS/and calculations, 1.28 X 44 is 56. So I would be within 1 MPH of accurate at this speed. Be within a 1/2MPH around the 30 MPH mark.
Senior User
Joined: Aug 2018
Posts: 158
Likes: 1
Here is what I believe would work. I do have the band style parking brake on the rear of the trans, but I still think this would clear that.
https://transmissioncenter.net/shop/...ratio-adapter/
"Up speed by 28%"
https://transmissioncenter.net/shop/...ratio-adapter/
"Up speed by 28%"