I have a 97 F150 4.6 automatic. I changed to 4:10 gears and changed the speedo gear. Since then my speed sensor kicks in just over 80 MPH. I have replaced the PCM, tried a Diablo chip(twice) and have since returned it, I tried an old Cobra extender, and my local dealer said they could have reprogramed my stock PCM but my truck was never offered with 4:10's so they can't do it. Any help is greatly appreciated.

 

What do you mean that the speed sensor kicks in at 80mph? Are you refering to the speed limiter?

Have you verified that your speedo is calibrated properly by either driving alongside someone with an accurate speedo, radar, or some other reliable means of determination?

From what little I've read here the speed limiter can be eliminated on most applications with Mike Troyer's chip but very few cannot be overridden. Most trucks have the limiter set to shut down between 97-103mph.

Maybe the incorrect speedo gear was installed ?? I'm sorry I could'nt be more of a help but it's all I got. Please keep us informed on how things turn out for you, I have the same engine/drivetrain and would like to know for the future if I do the 4:10 gears myself.

Good luck.

 

Where could you get a new speedometer gear? Would that help anything?

 

THANKS, I ALREADY TRIED THE SPEEDOMETER GEAR. I JUST SPOKE TO SUPERCHIPS AND THEY SWEAR THEY CAN CURE IT, BUT THAT'S THE SAME THING DIABLO TOLD ME. I HOPE THEY ARE CORRECT. I'LL KEEP YOU POSTED

 

I have a 98 4.6 auto 4x4 and also went with 4.10's. I put a 21 tooth gear in place of the 19 that was in the VSS and I am only 3% off at 70. I stayed with the 265-70-17 tires the veh came with. I also have a superchip and have exceeded 90 a few times but must be getting old did not want to get to the century mark or above. If your tires are smaller than mine you are going a lot faster on the speedo then you actually are. The super chip will remove the speed limiter and also give you more performance through out the power band but will not correct the speedometer or Tach. Enjoy

 

I should of mentioned it before but if and when you eliminate the speed limiter be aware that your tires may not be properly rated for speeds above the limiter's original setting.

If you plan on going over the "century mark" as George Kropp so eloquently put it, then make sure your tires are up to the task.

Good luck.

 

George Kropp,
I have a question for you. I have a '98 SC Lariat with 3.55 gears, and I've got a set of 4.10's I'm dying to install, but I have yet to find someone who can tell me where I can get a 23-tooth speedo gear. Even though I haven't checked the one I have from the factory, everything I've read makes me think it is a 20-tooth now (3.55, 4x2, 30" tire diameter). To correct the change from a 3.55 to a 4.10, I need a 23 to replace the 20, right? In your case, with a 4x4 with a 19-tooth, you probably got pretty close with a 21 (a 2-tooth change). The 21 wouldn't do me much good, only changing by one tooth. I've asked many people, and so far no one can tell me where a 23 is available (even though I have seen them mentioned in other threads, from which I cannot get any replies). Do you possibly know? Ford for sure doesn't make one for an F150, and they claim that the one for a Mustang won't fit. I appreciate any tips or recommendations. Thanks.

 

To answer your question about the 23 tooth gear-_No_. Some one said Steda or something like that. I believe they make products for Mustangs. Do you plan on larger tires? This will have the same effect on the speedo and tac. With 4.10's and 30" tires you must be getting off the line quick. With out a chip or other program to raise the speed limiter you must be hitting it if speed is your passion. I have read some where if you use to high a tooth count in the VSS it wears out very fast. Good luck with your search.

 

The formula I used was 4.10-3.55=.55 .55/3.55=.1549 0r 15.49%
Take the actuall number of teeth of the old gear and multiply by the 15.49%. In my case 19X15.49%=2.943. 19+2.943=21.943 or 22. Since 22 was not available I took the 21. Still off but close enough. Since you do not have the gears in yet (reread your thread) you might as well find out what you need before you start.