will swapping gears affect speedometer reading

[BobCarter]

I switched from 3.73 to 4.10's and was curious if this should adjust my speedometer, or is the speedometer gear not affected by gears.

 

[410Fortune]

yes it is effected, however larger tires can bring it right back to where it should be.

What year truck and is it 4x4?

 

[BobCarter]

Mine is a 99 2wd. My speedometer reads about 62 when I'm doing 70. I'd like to fix that if possible. Can I replace this tooth gear with a different one that would compensate for the difference? Would that mean I need more teeth in the gear or less?

 

[BobCarter]

Doesn't sound to me like anyone is 100% sure on this issue. I found my speedo thingy, its bolted to the top of the rear diff. I didn't have time to take it out though, I'm gonna look at it tomorrow.

 

[TheRookie]

I am sure. you will have to go get it recalibrated or buy the programmer. its just like okrazie said

 

[maypo59]

The sensor in the rear diff ( at least on my 99 Limited) doesn't have anything to do with speedometer. drove to ford store for parts with it unplugged. speedo worked fine, cruise worked fine, abs did not.

 

[wpurple]

The sensor in the rear diff is for the antilock brakes.
The VSS is located on on the tail of the tranny. (or the transfer case)
I believe that after 98 was the year they switched from using a gear to having to reprogram the computer.

 

[maypo59]

LOL, then the manual is wrong. period. or my speedometer and cruise works by magic. unplug yours and see what happens ;-)

 

[Okrazie1]

Well, I guess it's just obvious I don't know what I'm talking about, even though I own a '99, I've done a gear change, and I've researched this info in the Ford factory service manual, so I've deleted my posts from this thread. I give up!!

 

[Jefe]

Alright, to clear up the issue. 91-97 Has the senser with gear in the tailshaft or tcase. In 98 they went to a hall sensor (no gear) located in the same place. From 99 up they got rid of that sensor location and use the ABS system for the VSS. The ABS system has three hall sensors -2 up front and one rear. If any one of these sensors is plugged in you will still have VSS (but no ABS without all three). Since they use a hall sensor(s) from 98 on you either need to get your computer reprogrammed from ford, or you need to get a Superlift TruSpeed (or similar device, I know of one other but don't remember the name).

Now back to the original question. If you regear a 99+ the speedo will still be accurate since the sensors are reading axle speed. Only tire size will affect it. However, your tranny may act strange, as the engine and tranny will be turning at a different ratio than they expect. I'm sure Ford could help you there, its just a matter of how necisary it is.

 

[BobCarter]

I would agree. My gear ratio didn't seem to change the speedo but my tires did. I ended up finding a deal on a superlift speed calibration kit and will be installing it soon to fix the problem. The tranny shifts fine, but when you come to a stop it downshifts sort of funny because it thinks its going slower than it actually is