i need a new speedo gear for my 55 ford. it has a c4, 3.92 gears, and 235/60 r15 tires which measure about 25 inches in diameter. i was able to modify the 78 f150 speedo cable to go on my stock gauge, i just need help finding a gear since i broke the old one and have a different setup. i wasnt sure which forum to place this in but i know this website is where the experts are. any help is appreciated...for i am lost. oh, you might know the part number or the place to find what i need, i greatly appreciate it.

 

I have a 56 with a c-4 same rear end and tire. I'm using a 20tooth gear. I got it at Delta Mustang in Brentwood Califorina. I'm using a autometer speedo and it still indicated ~ 4mph faster than actual speed.

Good luck.

 

is the auto meter gauge and a stock gauge calibrated similiar? would say a 22 tooth fix that 4 mph difference? it seems to be the right place to start, at least i have i working speedo then, i dont ever use my speedometer anyways, i drive by the seat since i am in the work truck 40 hours a week. thanks

 

i just thought about it a bit, if i ran a 18 or 19 tooth i could correct your 4mph difference depending on whether the gauges were calibrated the same. maybe i should run a gear with as many teeth i can get so it looks like i am burying the needle stoplight to stoplight.....lol..

 

Based on Tacomalight's experience and if you have the same set up, you need a 21 tooth gear. Each tooth is good for about 4-5 miles per hour difference.

Vern

 

To slow your speedo you need to increase your teeth. Unfortunately, 20 teeth is the highest offered for the c-4. The 22 teeth will not work on a c-4.

Try using a 18 or 19 teeth on a stock speedo. You can get one at mid fifties or sacramento vitage ford for $10 bucks. I would replace the cable while your at it for $30

Have fun.

 

Here's a Formula for figuring out the correct gear.

(T*G*20.2)/D = Gear needed

T = Gear on tranny tailshaft normally 8 or 7 tooth
G = Gear Ratio
D = Tire diameter

(7*3.92*20.2)/26.1 = 21.24
So you need a 21 tooth gear

 

Alot of these gears can be had at your local Ford dealer. They may not have one on hand but can get them in 1-2 days. Here in Ct., we're lucky as the depot is in state. Some are obsolete, but many are still available. many of the gears can be swapped around, regardless of the application. It depends more on the pitch (right or left) of the teeth and the length of the gear. If I saw the gear you have now, I could probably steer you to a part number and you could check your local dealer. If you want, send a private message with your email address with "at" instead of @ and we can go from there.

Barry

 

thanks barry for offering to check up on that for me.. i im you a few mins ago.
i saw that on the tci automotive they list the 21 tooth gear in red and it fits c4, c6, aod. i couldnt find a price for it though. i would just assume go up the street n get one at the ford dealer for a quality part. i had a friend do that on his old galaxie when he stripped the gear. i used to work at a ford dealer, and i know if i ever wanted various parts pulled, i just had to walk in during a slow time,, otherwise it was hard to get a guy willing to do the footwork...lol...

 

thanks for the help, i just found one on ebay for 8$ in a sellers store.