speedo question
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speedo question
Many of the older cars have gears in the speedo that can be changed to FIX speedometer reading. I know changing tires changes reading but is there an adjustment or gear change in our speedo's?
Postmaster
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From: Langley, BC
It's a little plastic gear that goes into the tailshaft housing of your transmission, sealed with an O-ring and held down with a tiny 7/16" bolt (if I recall correctly). It's like a mini distributor hold down bolt. Undo the bolt, pull the cable out, pull off the speedo gear, and replace with one of a different tooth count. I think I read somewhere that each two teeth in a speedo gear count for 5mph but I'd take that with a grain of salt.
Lead Driver
Joined: Jul 2011
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From: On the Edge of the Desert
My speedo was reading about 10mph over, I went two teeth and got it almost spot on.
You'll have to do a little trial and error with which one you need. Ford sells them for a decent price. ($6) so try one and then another if needed.
You'll have to do a little trial and error with which one you need. Ford sells them for a decent price. ($6) so try one and then another if needed.
Ford Parts Specialist
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From: Simi Valley, CA
It's a little nylon gear that goes into the tailshaft housing of your transmission, sealed with an O-ring and held down with a tiny 7/16" bolt (if I recall correctly).
It's like a mini distributor hold down bolt. Undo the bolt, pull the cable out, pull off the speedo gear, and replace with one of a different tooth count.
I think I read somewhere that each tooth in a speedo DRIVEN gear, count for 5-7 mph.
It's like a mini distributor hold down bolt. Undo the bolt, pull the cable out, pull off the speedo gear, and replace with one of a different tooth count.
I think I read somewhere that each tooth in a speedo DRIVEN gear, count for 5-7 mph.
Some 1967/72 F100/350's have a nylon gear, some have a cast iron gear, some have a steel shaft that has a fiber gear riveted onto its end.
The nylon gears were introduced in 1960, used well into the 1990's. Have 16 thru 21 teeth, all are available from Ford. The most expensive is less than 6 bucks, the cheapest is 4 bucks.
And, the 6 or 7 tooth DRIVE gear is located on the output shaft of the trans. It could be steel or nylon.
Hotshot
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From: Phoenix, Az.
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Fleet Mechanic
Joined: May 2012
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From: peru kansas
i hate to barge in but i'm curious since i went from 4.10 gears to 2.78's my speedo reads at 42 mph when i'm actually doing 65 mph so would i need closer to 16 teeth or 21?
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Ford Parts Specialist
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From: Simi Valley, CA
Year, series, trans and rear axle type, tire size?
Hotshot
Joined: Mar 2013
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From: Phoenix, Az.
If a person needs to speed up the speedometer then you need a gear with less teeth. Think of it as with less teeth every tooth of the drive gear will grab and spin each tooth off the driven gear faster. 23 MPH is a big span. You might have to change the drive gear also. Which is prolly the reason Bill wants truck's info.
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
If a person needs to speed up the speedometer then you need a gear with less teeth. Think of it as with less teeth every tooth of the drive gear will grab and spin each tooth off the driven gear faster.
23 MPH is a big span. You might have to change the drive gear also. Which is prolly the reason Bill wants truck's info.
23 MPH is a big span. You might have to change the drive gear also. Which is prolly the reason Bill wants truck's info.
We know that the DRIVEN gear will be different, the DRIVE gear might/will (pick one) also be different.
Fleet Mechanic
Joined: May 2012
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From: peru kansas
66 f100 cccs originally had dana 60.2 from what you had told me before Bill, 9" from a 67 f100, 435np trans, 265-75-16's tires, also it has a sweep style speedo if that matters or not..... rearend gear ratios are out of an unknown large car with no info tag since it has been lost over the years but it was marked and cataloged as 2.78 gears on the fellas racing shelf.....any other info just ask i will see what i can remember or find out
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
66 f100 cccs originally had dana 60.2 from what you had told me before Bill, 9" from a 67 f100, 435np trans, 265-75-16's tires, also it has a sweep style speedo if that matters or not..... rearend gear ratios are out of an unknown large car with no info tag since it has been lost over the years but it was marked and cataloged as 2.78 gears on the fellas racing shelf.....any other info just ask i will see what i can remember or find out
Where's JEFFAFA when I need him? 
So, what exactly is the application? 1966 F100 Custom Cab NP435 w/a swapped in 1967 F100 9? Swapped in R&P in '67 F100 9" from a land yacht?
Since there was no 9" w/a 2.78 ratio, it's probably 2.75. But 1977/78 land yachts were available with 2.50 gears, 1978's with 2.47's. I hope these ain't it. 9" R&P's interchangeable 1957/86.
Fleet Mechanic
Joined: May 2012
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From: peru kansas
66 vin is F10YK862370....67 vin is F10YLA73601.....don't give up hope on me yet Bill i'm trying to be a smart little fella for ya....the 67 when i got it it had a c6 installed in it but still had the man pedal from whatever manual trans was in it before but the PO lost his left leg to cancer so he wanted a c6......the gear ratio's were up on a shelf with a whole stack of other 9" and 9"accessories (could it be a 9 3/8" possibly?) like i said he knew it was from some big car but didn't remember exact year make and model i do know it has a "hood" over the flange and lots of dirt and grease over it so if there is a casting number you need just tell me where to scrape......
Hotshot
Joined: Mar 2013
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From: Phoenix, Az.
Oh boy, I shoulda stayed in bed. Where's JEFFAFA when I need him? 
So, what exactly is the application? 1966 F100 Custom Cab NP435 w/a swapped in 1967 F100 9? Swapped in R&P in '67 F100 9" from a land yacht?
Since there was no 9" w/a 2.78 ratio, it's probably 2.75. But 1977/78 land yachts were available with 2.50 gears, 1978's with 2.47's. I hope these ain't it. 9" R&P's interchangeable 1957/86.
Where's JEFFAFA when I need him? So, what exactly is the application? 1966 F100 Custom Cab NP435 w/a swapped in 1967 F100 9? Swapped in R&P in '67 F100 9" from a land yacht?
Since there was no 9" w/a 2.78 ratio, it's probably 2.75. But 1977/78 land yachts were available with 2.50 gears, 1978's with 2.47's. I hope these ain't it. 9" R&P's interchangeable 1957/86.