ok i've done alot of searching and come up with some information, however i am still confused on what action i should actually take.

i upgraded my tires to 285/70/17's. i know my speedometer is off by a couple mph, i just dont know how many. i cannot change the speedometer through the computer because i have a 97 F150, so i discovered from searching that i need a new VSS gear. my truck is a 2wd F150 but my sticker says that my axle is code H-9, or a 3.55 ls. I thought ford told me once i had a 9.75 rear end, so i'm kinda confused about that. (i'm not sure if the axle code or number is important, just thought i'd let everybody know)

from what i've gathered i must have a VSS gear with 20 teeth, and that i would want to switch to an 18 toothed gear. I also think i've found information saying a ford service department wouldnt do this kind of labor correction, so i just want to make sure when im doing the actual change its in the right spot.

i looked under my truck and found a black cable running to some plastic houseing unit with a single bolt/nut on top of the transfer case (i think) Its the only thing i've found that looks like the descriptions of many of the people here. am i right?

sorry for the long post, just trying to figure things out. basically if anybody has any info for correcting a speedo with 285/70/17's on, and what VSS gear i will need, your help will be enormously appreciated. THANKS!
John

p.s i will be switching to 4.10 gears hopefully within two or three weeks. i have the 4.6L V8 and with these new tires i have found a slight power loss. are 4.10's a good idea for my set up? i only do road/highway driving and never tow anything. I read also that you need a speedo change again with a gear change, would i need to get another VSS gear at that point also? sorry again for the long post.

 

If you are going with new gears in a couple of weeks, then don't bother with the VSS gear change now. You are correct in that you will probably need the 18 tooth gear to correct for the taller tires and 3.55 gears.

I put in a 19 tooth gear to replace the stock 20 when I went to 31" tires and 3.55 gears.

If you go to 4.10, you will 'almost' be back to your original ratio with original size tires and the 3.55's, so a VSS gear change 'might' not be necessary.

It sounds like you have found the VSS part on the trans at anyrate......

You might find that you will need a 21 tooth gear after the gear swap. Just depends how far off you actaully are at that point.

Oh, if you have the 4.6, that means you have the 8.8" rear end...... Count the cover bolts too. 10 = 8.8 and 12 = 9.75

Mitch

 

By that tire size and gear ratio with a 4r70w transmission having 8 teeth you will need a 18 tooth speedometer drive gear to be closest but it will not be perfect because it would require an 18.45 tooth gear.
Alan

 

dirtyd0g,

We just purchased a '98 F-150 4X4 with I believe 285/75/16's tires for Mike's daughter. Is there a way to calculate the correct speedometer drive gear or is there away to electronically make the correction?

TIA

 

ok went to a ford dealership near to where i work today...very dissapointing.
I asked for a 18 toothed VSS gear and explained that i was recalibrating my speedo because i have larger tires. I told him i think that its just a little plastic gear, and he went to his computer and printed out a diagram of the whole rear axle of my truck. It was a 97' print out and he said i needed a whole new speed sensor that mounts on top of the tranny (or gear housing place) i said how do i install that and then he said well it would require a complete overhaul of my instrument panel, removing, precisely recalibrating the needles and measuring stock tires to the current tires. (that tire part makes sense)

But i thought all i need is a little plastic gear?!?!?! He also showed me what as he refers to as "a later model speed gear set up" and it was a plastic gear but it was much bigger, lenght wise and width. I dont know what to do, i wanted to just get the gear till i get the money for 4.10's, then i could take it out and put the stock back in. should i see if another ford dealership gives me any other ideas/THE ACTUAL GEAR I NEED!

thanks again for the help, and sorry the post is long again.
sincerely, John

 

You found an idiot at the fdealership all you need is that little plastic gear.
Call Dan @ T&C ford tell him you need a 18 tooth speedometer gear that will work with a 4r70w transmission.
Link

 

I need your rear gear ratio to get a calculation, but yes you will need a different gear.
Alan

 

Alan,

The gear ratio is 3.55. Please let me know if you need further information. Thanks for the help.