Since the lift and 35,s my odo/tripometer is not reading accurately. Example, I actually traveled 240 miles on a recent trip and the odo/tripometer showed 218.

Since mine is a 98, no programmers will help with adjusting for the tire size and I was told I had to replace the speedometer gear. Has anyone done this and how do I figure out which one to put in? Thanks

 

its very simple and costs about 20 bucks and takes 15 minutes. but you might need to regear first. what gears do you have now?

 

i will try to help you a little. this may get a little lengthy, so bear with me. i'm not 100% sure if you have a gear or sensor. my guess would be gear because you have been told that programming will do no good. ok, with that being said, the gear is located on the side of the tranny towards the rear, (not sure which side), but you can't miss it. it would have a cable and NOT wires running to it. it only has 1 screw and a metal clip that holds the assembly to the tranny. with that removed, the assembly can be removed from the tranny, you may have to tug on it a little, but it will come out. then there is a metal clip that holds the plastic (nylon) gear on the cable, remove it and the gear comes off. you will lose some fluid out of the tranny while doing this. there are a few things you'll need to know before you purchase one from Ford. first, does your gear have teeth going to the right or left. second, how many teeth does your gear actually have and third, how many tenths in a mile is your speedo off. with your VIN # and the #'s off of your rear-end, the parts dept. at Ford can find out what gear you have. if this is something you want to find out for yourself, then you'll have to remove yours. i said earlier, teeth to the right or left. with yours removed, the base where you took the metal clip out, which way are the teeth going to the top of the gear, right or left? second how many teeth? there is a # stamped on the top of the gear (i've seen them as low as 15 and the highest is 21) or you can just simply count them. you definetly need to know for sure how many tenths you're off. go through a measured mile, (i usually reset the trip to 000.0 at the line in the road and stay in the same lane to the end of the true mile) your odometer will not be reading a full mile because you have put bigger tires on your vehicle which slows it down. (traveled 240, actually read 218) bigger tires and/or more teeth on the gear will slow it down, smaller tires and/or less teeth will speed it up. you need a gear with less teeth on it, if in fact your odometer doesn't read a full 1 mile. now, (i hope i haven't lost you), in my past experience, 1 tenth is about 3 miles an hour off, so if your reading .9 and the end, drop 1 tooth less or 1 tooth per tenth off. i have seen in the past where i was between 1 & 2 tenths off, so i personally went to the next up (2 teeth), simply because i wouldn't run the risk of getting a speeding ticket. i hope this helps, and if you do have any more questions, i'm here as well as others.
BTW, what part of NC are you in?

 

Use this link or call them. they will know exactly which one you need

http://www.transmissioncenter.org/Fo...eter_Gears.htm

Calculator

http://www.bgsoflex.com/speedo1.html

i got the 21 tooth p/n #82 and it was a super easy swap. like posted above you either have a 7 or 8 tooth drive gear most likely a 7 but if you pull the shaft out and look what color it is you can find out which one you have and need.

the reason i said about the gear swap first is you might not be able to get a gear to correct it first or you might already have a 21 tooth like i do. b2therad has a 4.6 auto and did 4.56 swap also with 35's and had the 21 tooth stock so he was fine.

 

Thanks for the info, sounds like its what I am looking for. As far as re-gearing, no plans to. [Im in Winston Salem]
I checked yesterday with exact known mileage from point A to B and it was about .3 off. The 240 traveled and 218 registered is throwing me way off.

 

well, i checked with the ole' trusty calculator this morning and it looks like your speedo is only registering 90% of your mileage. (90% of 240 is 216, pretty close) which seems to me that it boils down to being off .1 tenth in every mile. so right now, your speedo is reading 60, you're actually doing about 65-66. with 1 tooth LESS on the gear, your speedo will increase 2-3 mph, with 2 teeth LESS, it shoud increase 5 maybe 6 mph. hope this helps

 

I greatly appreciate you checking into this for me, however Im going to throw you a curve. A few years ago I put a white face panel across the factory one. When the needles were put back on, they did not line up properly. So I have been running anywhere between 7-8 mph slower than showed on the speedo.
So I guess I could be reading pretty close to actual speed, but the mileage is off. Would the gear still help that?

 

Bumping this back up. I havent received a reply yet from the above link. I had a 19 in and replaced it with a 20. Picked up .2...towards the actual mileage reading. Any ideas?