Correcting the speedometer

I've swapped out the 3.00 gears in the rearend for 2.79 and was wondering if there's a way to determine if I can change the gear for the speedometer to read the correct mph. If that's even possible. I have a 73 Maverick 302 w/ C4 tranny.

 

With the taller 255/60/15 I have on back, to correct mine I had to swap from the 20 tooth drive gear used with 3.00 to a 18 tooth that was used with 2.79...

Yours should be same but it you have larger than stock tires may need a gear with less teeth... Each tooth subtracted from gear count will increase speedo reading approx 3.5 MPH... There are calculators on line but since I keep a supply of gears on hand I just guess, hit it first time on my Comet...

 

I have the factory size 14's on mine. Just a little wider. When cruising at 60mph according to GPS, my speedometer is reading 54. Are the gears available online and does the whole speedometer cable have to be replaced?

 

Why would you go from a 3.00 to a 2.79?

In any case, to correct your speedo, the driven gear that goes on the end of the speedo cable where it connects to the transmission must be changed. There is also another way -- there's an adapter that you can buy to correct it. I think it is sold by Bowler Transmission.

 

I swapped it out to get a little better mileage. Plus I got the gears at a steal. I was needing to replace the seal and gasket anyways. I'll find out what the tooth count is on the speedo gear since it's easy to get to before I order anything. Go from there. I'll check out what Bowler has to offer.
Thanks Larry

 

Sounds same as mine was with larger tires, by changing from 20 to 18 tooth gear mine now reads 61 when I'm doing 60...

Gear is held on trans end of cable with a small clip, will take longer to get car in air than change gear...

 

So this gear swap is fairly easy? Any special tools?

 

Just a 3/8" or 7/16" wrench and small screwdriver to pop clip loose...

 

Good deal. Thanks

 

Ok, I checked the tooth count on the speedo gear and it's 19 teeth. Easy to get to. Raised the front of the car up a few inches and was able to slide under.

 

To slow down the speedometer increase the teeth on the gear, to speed up the speedometer decrease the teeth. If you remove the gear from the cable and take it to a Ford house they will probably have what you need. The gears also have a left hand or right hand slant and they are not interchangeable.

 

AutoKrafters has them for less than $10. Just need to determine which one I need.

 

AFAIK the reversed pitch tooth gears are only for trannys that have cable opening on passenger side(Top Loaders)...

 

I gained more mpg when I stepped up to the 3.00 from the 2.79. Best I can figure out why is because the little bit of extra ratio made life easier for my 6 cyl engine to get up and maintain speed. With the 2.79 I was in the gas pedal deeper and longer going up hills or going redlight to redlight.

 

With my 302, the change in performance isn't that noticeable. I can tell the difference a little in the rpms at highway speeds.