Speedometer off

[stang0303]

I have a 99 f250 7.3. the truck has smaller tires on it they are 70's instead of 75's. I got the superlift speed calibrator because it was 10mph to fast. I followed the instructions and put the speed calibrator on. after i installed it its been acurate untill about 40mph and then its 5 mph to slow and then as i increase my speed it even gets further out of wack 10mph to slow and so on. Does anyone know what is causing this?? Do i need a new instrument cluster? Speed sensor? something im missing here with the calibrator? Any help would be greatly appreciated!

[Freedombyforce]

your gonna need more info than just 70 to 75. What size are the tires that are on it now? Did you buy the truck with big tires on it and then take them off?

[stang0303]

yeah they are stock except the side wall height. I told me in the superlift manual to do 10 turns on the calibrator which i did but like i said it is true speed slower then 40 mph according to my gps and then the faster you go the more off it gets. It had these smaller tires when i bought it. the guy i bought it from lowered it in the back with 2" drop shackles and he said he liked the smaller tire look i guess. I bought some 20's for it and going to put them on but i guess he said they are the same height just more rim.

[stang0303]

no responses not sure what to do

[Term3]

Back when I had a lifted truck with big tires I took it to a local shop that had a drive on dyno and they ran it thru all the gears and from that they made a speed compensator to correct my odometer.

[stang0303]

I bought 20 rims on it with 275/45/20 tires hopefully when i put them on in the spring i will take it to get calibrated. I bought the calibrator but it still isn't right i must be doing something wrong i installed it right. hmmm

[Term3]

Originally Posted by stang0303

I bought 20 rims on it with 275/45/20 tires hopefully when i put them on in the spring i will take it to get calibrated. I bought the calibrator but it still isn't right i must be doing something wrong i installed it right. hmmm

Just do what I did as the place I went to builds a custom unit for EACH vehicle. Don't go to a place that just pulls a converter off the shelf and install it.