Speedometer gear help
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Cargo Master
Joined: Apr 2010
Posts: 2,600
Likes: 64
From: Billings, MT
Speedometer gear help
'77 2wd F-150 with a C6. 4.10 rear gears and 29" tall rear tires. Currently has an 18 tooth speedo driven gear and the speedometer reads about 20% too fast.
I believe the c6 has a 7 tooth drive gear but I'm not sure. I'm thinking I need a 19 or 20 tooth driven gear to get it right but I'm not sure.
At one time I had found a really good speedo gear calculator but now I can't.
Help!
I believe the c6 has a 7 tooth drive gear but I'm not sure. I'm thinking I need a 19 or 20 tooth driven gear to get it right but I'm not sure.
At one time I had found a really good speedo gear calculator but now I can't.
Help!
Fleet Mechanic
Joined: Dec 2007
Posts: 1,512
Likes: 340
From: Wildwood Pa
If your speedo is reading 20% fast with an 18 tooth gear, you need a gear with 20% more teeth to slow it down to be accurate. That comes out to a 21.6 tooth gear. Have to try a 21 & 22 & see what gets you closest.
21 tooth are out there, 22 & 23 seem to be harder to find.
Here's a source for a set of gears, more than you need, but it includes a 21. I have personally used the gears this vendor sells with no issues, very happy with them. http://www.ebay.com/itm/Ford-SPEEDOMETER-GEARS-7-PIECE-KIT-with-GEAR-CLIP-NOS-Mustang-T-Bird-/141921174527?vxp=mtr
21 tooth are out there, 22 & 23 seem to be harder to find.
Here's a source for a set of gears, more than you need, but it includes a 21. I have personally used the gears this vendor sells with no issues, very happy with them. http://www.ebay.com/itm/Ford-SPEEDOMETER-GEARS-7-PIECE-KIT-with-GEAR-CLIP-NOS-Mustang-T-Bird-/141921174527?vxp=mtr
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 787
From: Simi Valley, CA
If your speedo is reading 20% fast with an 18 tooth gear, you need a gear with 20% more teeth to slow it down to be accurate. That comes out to a 21.6 tooth gear. Have to try a 21 & 22 & see what gets you closest.
21 tooth are out there, 22 & 23 seem to be harder to find.
Here's a source for a set of gears, more than you need, but it includes a 21. I have personally used the gears this vendor sells with no issues, very happy with them. Ford Speedometer Gears 7 Piece Kit with Gear Clip Mustang T Bird | eBay
21 tooth are out there, 22 & 23 seem to be harder to find.
Here's a source for a set of gears, more than you need, but it includes a 21. I have personally used the gears this vendor sells with no issues, very happy with them. Ford Speedometer Gears 7 Piece Kit with Gear Clip Mustang T Bird | eBay
These gears have been available from Ford since 1960, also available from auto parts stores.
Fleet Mechanic
Joined: Dec 2007
Posts: 1,512
Likes: 340
From: Wildwood Pa
Yes, aftermarket has 22 & 23 tooth driven gears.
So, there is such a thing, just not a genuine Ford part. 23 Tooth Ford Speedometer Driven Gear | eBay
Not a big deal, just wanted to let folks know they are out there. Sometimes a gear like this is the easiest & cheapest way to get on the road.
So, there is such a thing, just not a genuine Ford part. 23 Tooth Ford Speedometer Driven Gear | eBay
Not a big deal, just wanted to let folks know they are out there. Sometimes a gear like this is the easiest & cheapest way to get on the road.
Posting Guru
Joined: Jul 2013
Posts: 1,685
Likes: 2
From: Oregon
Late model restoration has a speedo gear calculator. Hope it helps. They also have gears up to 23 tooth, maybe more I dont remember at the moment.
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