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?

 

Yes. It's on the tail housing of the transmission. Easy to change, one bolt, one clip.

 

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.

 

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.

 

When I'm at 40mph the digital road signs clock me at 60km/h, when it should be 64km/h. I've yet to grab a GPS and see if my speedo is actually off or not.

 

The DRIVEN (end of the cable) gear may not be nylon, because the OP failed to mention what year the truck is, or which trans it has.

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.

 

On the nylon gear each tooth is 4-6 MPH. Depending on tire size etc.

 

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?

 

Year, series, trans and rear axle type, tire size?

 

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.

 

I wanna see which DRIVEN & DRIVE gears the parts catalog calls for. OP didn't say what the tooth count is...of the DRIVEN gear his truck has now.

We know that the DRIVEN gear will be different, the DRIVE gear might/will (pick one) also be different.

 

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

 

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.

 

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......

 

I"m here back from lunch Bill. I'll grab this one. Checking to see what this tire size equates to in the old style tire sizes inbetween phone calls.