I have a 98 f150 which we all know the speedometer and odometer are not electronicly adjustable. I upgraded my tires and went to a larger size and would like to return back down to stock.

I went to the local parts store nd told them what i wanted to do and they told me that i needed a speedo gear that sits on my transmission. The problem is that i just replaced the tranny and i dont remember seeing a cable where a gear could sit.

Further more tehy told me that i would need to know the tooth count to get a modifed one.

I went to the ford dealer here in town and they were less than helpful and did me no good.

I turn to you guys for help. Does anyone know what i need. Im running on 285-75-16's.

HELP

 

Here is how you can figure out what driven gear is needed if your trans uses one.
Driven gear teeth = output shaft number of drive teeth times axle ratio times tire revolutions per mile divided by 1000.
This is right out of the Ford Motor Sports catalog.
Example; 7t x 3.73 gear x 815 revs per mile / 1000 = 21.3 teeth or the nearest one to 21 teeth.
The tire revs per mile you get out of the mfgers catalog on your tire.
What you need, I can't say at the moment without enough info.

 

I have a similar problem. I was recently running 305/70/17's on the truck and the speedo was obviously completely incorrect. The truck is lifted 7 inches. I'll be taking the lift off tomorrow. I put on 265/70/17's today (which are just about stock size) and the speedo is still completely off.

Why would this be happening if the tires are stock? Does the lift have something to do with it?

Thanks.

 

There are aftermarket modules that electronically adjust the speed signal. Maybe your truck has one. Are you the original owner?