OK so I put on a larger set of tires than stock ones were. So now my speedo reads somewhere between 5 - 10 MPH slower than I am actually going. Not only that but my tranny shift timing has changed and engine performance suffering.

So I have been looking for information on what to do to correct this. It seems like I need to change the speedometer gear.

Well today I crawled under to take a look. What I expected to find was a speedo cable entering at the tail end of the tranny. What I found was an electronic pickup. I disconnected the wires and drove around the block...no speedometer reading. Hmmm....okay so I found the speed sensor.

Now here is the question...if I remove the speedo sensor from the transmission should there be a gear on the end that can be replaced? If so, how do I calculate which gear to purchase?

Thanks,
Bill


'97 F-150 4x4 4.6L Automatic
265/75/R16
3.55:1

 

I would check out the superchip tuner, w/ my truck(00 f-150 4x4) I change it right in the computer, all you do is measure the tires and punch it in, you can also change your shift poinst to a certain degree and how hard it shifts, and gives the motor a little more jam.
Nick

 

Yes you do need to change the gear. I am going through the same thing right now. I recently put the same size tires on my truck and I calculated that I need a 19 tooth gear. I also have the 3.55 rear end so you would need the 19 tooth gear to correct it. All you need to do is remove the nut that holds the assembly into the transfer case and then there is a clip that holds the gear on. As far as the shifting goes I have heard that there are tuners out there that will let you change the shift points of the trasmission to compensate for the new tires.

 

I could be wrong but I think changing the VSS gear will straighten out the shift points as well. Also what tire size did you go with? I just put on 285/75/16 with 16x10 wheels the truck looks great, however I will be getting 4:10 or 4:56 gears dropped in it shortly.

 

I'm currently running the stock size of P235/70/16 tires on my 04 F-150 4x4 Hertiage with 3:55 gears. I was going to replace mine with the 265/75/16 . Someone told me just to take my truck to the local dealer & have them hook it up to thier computer & that they could change everything. My truck is still under factory warrenty & Gas mileage is very important How will the bigger tires affect my gas mileage?

 

On the highway I have found with my bigger tires it improves mileage a little, not alot. And in city it seems to really decrease my mileage.

 

I just switched out my 235/75/16's to 265/75/16's. I took it to the dealer and they reprogramed the compter for the new tire size. They said that they could do this up to two sizes bigger then stock. I can tell you that the 235's really look bad on these trucks. 265's make a huge difference in looks and performance!!

 

You can have the computer re-programed at the dealer to match the tires.
Acording to my local dealer (you never know) they only show one spedo gear because the computer can be changed so no selection. Maybe you can match up something.

 

Are you sure? I am pretty sure that you need to chage the speedo gear to correct the speedo on the 97 and 98's. I recently bought a new gear for my 98 for $10, I have not yet had a chance to put it in. I tried the Ford dealer, but they did not have the gear I needed so I went to a local 4x4 shop and got one from them. Even if it is possible to re-program the speedo, I would recomend changing the gear. It is going to be a lot cheaper than having the dealer re-program the computer. I will put my gear in sometime this weekend and let you know if it changes the shift points also.

 

I don't know about the 97-98 mine is a 2000. It only cost me $40 bucks and they also did the cruise control update at the same time. It only took about 20 minutes.

 

I'm almost positive that they switched to the computer controlled in '00, before that it is a gear you have to swap out.

 

Im having the same problem in a 97 i have 35in tires and 4.56 gears does anyone know where i can buy the speed sensor gear from. thanks kevin

 

Funny thing.
I just changed ring an pinon gears on my 97 150 and am going to the dealer tomorrow morning.

Mine has the electric pickup/speedo gear on the trans so I am planning on getting the ratio changed in the computer (that's what Ford said). I asked a while back and the parts guy said only one speedo gear shown so.....

I will see and let you know.

BTW.
I did the ratio change on my 2wd Explorer last month, it has no trans speedo, only a sensor on the rear end so all well and the speeo is right.
Good news went from 4:10 to 3:27 and went from 18mpg to 22mpg. that's what I wanted.

 

steeda.com has them but i only see up to 4.10 cant seem to find anything for 4.56

 

Here is my update:
Went to the dealer, service got on the phone and called someone in the building then told me that on a 97 they can't change the computer, I need to change spedo gears.

Went back to parts again, got lucky and got a smarter one this time.
I tell him what I was told before he looks it up on the computer and says it only shows one. It turns out he and the other guy were looking at the drive gear not the driven.
When we figure that out he gets a book (a good sign) an we look it up by year/trans/ratio/tire size and boom I got the gear. I put it in and all looks good.

There were many choices of gears and the 1 tooth for 3 mph rule panned out too.
I was off about 10mph and the book showed 3 teeth less.

Always get a second opinion.