im going to be lifting my 2wd supercrew and getting 35s. im wanting to regear with 4.56 i guess. with that said after they are installed i know my speedo will be off, but how will it shift? will it stift like factory? meaning the same speed or shift too soon? will i have to get a programmer to make it shift correctly or am i too cautious?

 

You should get a programmer.

 

yeah, your going to need a programmer to adjust your speedo for the tire and gear change. and you can adjust the shift firmness and what rpms you want it to shift at too.

 

so if a 4.2 engine decided to get 4.56 and 35's what would we do to program....cuz i cant find anything for a 4.2 and dont want a canned tune

 

you have a 97. ford used a VSS gear from 97-98. you need to buy a gear that matches your combo.

a VSS gear is a small plastic gear that goes in the transmission that tells the truck how fast it is going.

 

well i dont care if the speedo is off i can use my gps for that. it shifts firm enough right now. im just asking if the gear change will make the truck shift way too soon. Ex: going 20mph in real life would it try to be in od or something like that. or lets say if i dont get a programmer will everything else be ok?

 

No its not going to be in OD going 20mph. Gears just multiply your torque. That means it's gonna get rolling easier and when your cruising at about 50-60 you hit a fairly steep hill, its not going to down shift like it would if you had stock gears and big tires. Transmission wear. If you went to 4.10 gears and 35" tires then your gonna be almost the same as stock power/acceleration.

Big tires raises your gear ratio(ex. 3.55 is higher gear than a 4.56) Going to a lower gear is GOOD for your transmission/driveline when you have large tires.

 

Not correcting the speedo WILL affect the transmission. The PCM will be getting the wrong vehicle speed input.

 

humm ok i guess if im going to put gears i have to change the speedo?

 

No, you have to reprogram the PCM for the new gears.

 

thats what i ment.