speedo drive gear
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4wd High
Joined: Jun 2020
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speedo drive gear
recently bought a 66 f 100 speedometer did not work so went to replace the cable and found no speedo drive gear in the tranny. Any one know how to figure out which drive gear to get there are all sorts of different ones with different spline counts truck is a 352 with 4 speed(T-18) and 3.55 gears and has stock 15" tires.Thanks in advance for any help
Tuned
Joined: Jul 2016
Posts: 469
Likes: 60
From: TN.
There are all kinds of calculators on the web, just pick one.
https://www.inchcalculator.com/speed...ar-calculator/
https://www.inchcalculator.com/speed...ar-calculator/
Lead Gopher
Joined: Aug 2012
Posts: 10,051
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From: Seattle
I don't think the speed calculators give Ford part numbers.
I believe you'd probably need part number:
C3OZ-17285-C - Drive Gear - 7 tooth.
Search the forum for that part number and see what you can read about. NumberDummy has posted that number more than once.
Sometimes people mistake the O (oh) for a 0 (zero) and you can find the part number sometimes only using the zero. One on eBay like that right now. None using the correct part number.
New OEM Ford C30Z17285C Steel Speedometer Drive Gear 60's-70's Mustang F-100 | eBay
And potentially 3 still at the NOS vendors.
NEW OEM C3OZ-17285-C in-stock at Ford Parts Locator (rearcounter.com)
I believe you'd probably need part number:
C3OZ-17285-C - Drive Gear - 7 tooth.
Search the forum for that part number and see what you can read about. NumberDummy has posted that number more than once.
Sometimes people mistake the O (oh) for a 0 (zero) and you can find the part number sometimes only using the zero. One on eBay like that right now. None using the correct part number.
New OEM Ford C30Z17285C Steel Speedometer Drive Gear 60's-70's Mustang F-100 | eBay
And potentially 3 still at the NOS vendors.
NEW OEM C3OZ-17285-C in-stock at Ford Parts Locator (rearcounter.com)
Tuned
Joined: Jul 2021
Posts: 486
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If it's the one on the end of the cable, those are easily obtainable. In fact I bought an assortment pack. Amazon I think.
Did the calculator thing to get it close, ended up with a one tooth difference from that. It now reads about one or two MPH off at 60mph.
Did the calculator thing to get it close, ended up with a one tooth difference from that. It now reads about one or two MPH off at 60mph.
Lead Gopher
Joined: Aug 2012
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From: Seattle
Just so anyone reading this knows if not already. There is a Drive Gear inside the transmission than turns the Driven Gear that is attached to the speedometer cable. The Drive Gear and Driven Gear need to be correct for each other or there will be problems with gear mesh. Generally, the Drive Gear only has choices of 7 or 8 teeth while the Driven Gear may have something more like 17 to 21 teeth. The Driven Gear is the one that provides for the more granular selections and is also much easier to swap out.
Lead Gopher
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From: Seattle
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4wd High
Joined: Jun 2020
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thanks for all the info wish old driven gear was in there would be a lot easier lol > think I will go to Ford and see if we can figure out how many teeth the drive gear has so I can match up the driven gear and if that don't work I am guessing I will have to go into the rear of the trans myself and try toi figure it out
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4wd High
Joined: Jun 2020
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thanks again for all the replies I ended up picking up an endoscope off of Amazon so I could figure out the spline count on the drive gear on the output shaft and I also wanted to look for the old driven gear in case it fell off inside but was just plain missing then I used to calculator and found out I needed to 18 spline driven gear so it is on its way and should have a speedo soon
Lead Gopher
Joined: Aug 2012
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From: Seattle
While you wait if you wanted to at least partially test the function of the speedometer needle to respond to the spinning cable core you can do like in this quickie video I recorded for a fella a few years ago. This won't check accuracy since there are no gears involved but it's something to try. I'll add that the battery powered driver I was using probably didn't have the torque to hold the needle real steady. But that's not really the point of this test as it's more about just making sure there is some response.
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