Speedometer Gear
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,455
Likes: 4
From: Western Kentucky
Speedometer Gear
I took the 70 out for a little drive today, and thought I would check the speedometer. I thought it was slow , but it is slower then I thought. When the speedometer is right on 50 the GPS says 57. My question is, I have got a 19 tooth gear in the transmission now, which gear do I need. If I remember right one tooth is about 3 mph, but my old brain may not be remembering right.
5th Wheeling
Joined: Jun 2010
Posts: 38
Likes: 2
From: Kalamazoo, MI
I have a 17 tooth in my C6 right now that reads fast (speedometer shows 70 when GPS says 55). I ordered a 21 tooth. 17 tooth would be yours if you would like.
You can tell what gear you need by using some simple math. If your speedometer is reading slow:
(Speedometer speed/GPS speed)*number of teeth
Flip those if your speedometer reads fast.
so
(50/57)*19 = 16.666 or 17.
You can tell what gear you need by using some simple math. If your speedometer is reading slow:
(Speedometer speed/GPS speed)*number of teeth
Flip those if your speedometer reads fast.
so
(50/57)*19 = 16.666 or 17.
Thread Starter
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,455
Likes: 4
From: Western Kentucky
I have a 17 tooth in my C6 right now that reads fast (speedometer shows 70 when GPS says 55). I ordered a 21 tooth. 17 tooth would be yours if you would like.
You can tell what gear you need by using some simple math. If your speedometer is reading slow:
(Speedometer speed/GPS speed)*number of teeth
Flip those if your speedometer reads fast.
so
(50/57)*19 = 16.666 or 17.
You can tell what gear you need by using some simple math. If your speedometer is reading slow:
(Speedometer speed/GPS speed)*number of teeth
Flip those if your speedometer reads fast.
so
(50/57)*19 = 16.666 or 17.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 783
From: Simi Valley, CA
I took the 70 out for a little drive today, and thought I would check the speedometer. I thought it was slow , but it is slower then I thought. When the speedometer is right on 50 the GPS says 57. My question is, I have got a 19 tooth gear in the transmission now, which gear do I need. If I remember right one tooth is about 3 mph, 
but my old brain may not be remembering right.
but my old brain may not be remembering right.Ford offered 16 thru 21 tooth nylon gears that are still available from Ford & autoparts stores.
Be aware if the truck has P-metric radials, the speedo will never be 100% accurate, as P-metrics are a different shape than the original bias ply tires.
Pic: Type 1 - 2 - 3 are the nylon gears noted above. Be aware which way the teeth run, because some nylon gears used in cars have teeth that run this-away: \\\\\
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
I have a 17 tooth in my C6 right now that reads fast (speedometer shows 70 when GPS says 55). I ordered a 21 tooth. 17 tooth would be yours if you would like.
You can tell what gear you need by using some simple math. If your speedometer is reading slow:
(Speedometer speed/GPS speed)*number of teeth
Flip those if your speedometer reads fast.
so
(50/57)*19 = 16.666 or 17.
You can tell what gear you need by using some simple math. If your speedometer is reading slow:
(Speedometer speed/GPS speed)*number of teeth
Flip those if your speedometer reads fast.
so
(50/57)*19 = 16.666 or 17.
Curious, I always went by each tooth being 3-5 MPH. Then did the math from there.
5th Wheeling
Joined: Jun 2010
Posts: 38
Likes: 2
From: Kalamazoo, MI
You can just have it. It's just going to sit around in a pile and collect dust otherwise.
Someone posted a picture above of the types of gears. This trans uses 2a type gears, make sure yours is the same.
Someone posted a picture above of the types of gears. This trans uses 2a type gears, make sure yours is the same.
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Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Types 1 and 2 are listed for A/T. Shorter tooth gears like 2a are listed for M/T. The area where the clip slides on is humped on a M/T gear though. Which does not show in Bill's pic.
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5th Wheeling
Joined: Jun 2010
Posts: 38
Likes: 2
From: Kalamazoo, MI
Its also a later model (early 80's) C6.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 783
From: Simi Valley, CA
The 16 thru 21 tooth nylon gears are the same from 1960 into the 1990's, maybe later.
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,455
Likes: 4
From: Western Kentucky
Thanks Guys for all the replies, and thanks Lneilinger for the offer. I think I'll go to Ford in the morning and pick one up. My son are going to a Cruise In tomorrow night and it would be nice to have it right.
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