Speedometer gear
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Junior User
Joined: Aug 2006
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Speedometer gear
My 1956 F100 has a wildly optomistic speedometer. It reads 50MPH when I would guess that I'm only doing about 35MPH. I'm betting that some time in its 50 year history someone replaced the differential but not the speedometer gear. is there someplace where I can buy a speedometer gear that might be closer to the right one? My transmission is a T98 four-speed.
Thanks for the information.
Thanks for the information.
Posting Guru
Joined: Aug 2000
Posts: 1,849
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From: S.C.
There are some pvendors on the internet that sells them once you decide the number of teeth you need, there are also some sites that will help you calculate the number of teeth based on gear ration, tire width, etc. I went to a Ford dealership and got mine from their service shop.
Jaye
Jaye
Senior User
Joined: Oct 2003
Posts: 358
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From: Joyce, WA
I went to my local auto transmission shop for mine. They do both sticks and auto. Had a whole tray of them. $12 and I was set. I figures I was off by 20 percent and we went up two counts on the gear.
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
In general, each tooth is worth about 5 MPH difference in speed. Since you are reading a higher speed than you should, you need a speedometer gear with more teeth. I'd take your truck out on a road with measured mile markers and a stop watch and figure out what 60 MPH is on your speedometer first and go from there to determine how far off it is and how many teeth you need. 
Logistics Pro
Joined: Dec 2005
Posts: 4,644
Likes: 55
From: Moro Bay, AR
I have several T-98 trannies laying around and they all use the same metal speedo gears. Every application I have seen with a T-98 used an adapter box between the trannie and cable to correct the speedo.
