diff upgrade

[xr62nv]

Own a stock au xr6, wanting to upgrade to a 3.9 diff ratio. Is the speedo the only thing that needs to be re-calibrated or do the shift patterns go out too?
anyone carried out this mod on an au yet? any help is appreciated.

[sly]

Presumably it's automatic? Yes the shift points need to be recalibrated else it won't change up at WOT. Easily enough done if you already have a flash box. The wiring diagram shows the speedo is driven by the PCM, I'm not sure if reflashing for a shorter diff will make the speedo read correctly or if you still need to get a different drive gear.

[Mechan1k]

in the AU ... you will need the correct drive gear for the transmission.
Not sure if this will sort your shift points out though ... I hadn't thought of that ... as I am looking at going 3.7's for my ute.

[xr62nv]

yes the car is an auto... how much is the estimated costs of getting the shift points adjusted. Also where would i need to go to get this done, anywhere in sydney?

[sly]

Anyone who does the CAPA Ford Flash can do this for you. The dealers are on the CAPA website. Sounds like you don't have a flash box yet. Check the deals in the site sponsors' forum, you should get a flash box for $495 plus postage with generic tunes. Don't pay $795 or $995 for it.

[FGII-XR6]

here is one going cheaper. unlocked and ready to go http://www.fordforums.com.au/showthread.php?t=11206871

[xr62nv]

so is purchasing the flash box and plugging it in all i need to do. Or do i have to buy it then go get it tuned to suit my car.

Also has anyone here changed diff ratios and know for sure weather the shift patterns need to be adjusted or if its just a speedo issue as some people have been telling me the shifts are controlled by the cars revs not speed and diff change wont affect the shift points.

however no one has been able to give me a definite answer, not even the diff place

[FGII-XR6]

Originally Posted by xr62nv

so is purchasing the flash box and plugging it in all i need to do. Or do i have to buy it then go get it tuned to suit my car.

Also has anyone here changed diff ratios and know for sure weather the shift patterns need to be adjusted or if its just a speedo issue as some people have been telling me the shifts are controlled by the cars revs not speed and diff change wont affect the shift points.

however no one has been able to give me a definite answer, not even the diff place

you need to get it setup for what you have and yes it does have to be done as the ECU looks at RPM and speed to detemine the shift points change the diff and it gets confused. i put a 3.45 in min and the shifts were a bit weird till I put an XR6 ECU in which expects to see a 3.45

[Mack 6]

Since you have an Auto (I do), you can change the speedo transducer(?) gear to suit
Enter the relevant information into this calculator
http://www.fordmods.com/forums/documents.php?doc=30

As for the location of the gear from memory it's an 8 or 10mm bolt holding the transducer in on the rear drivers side of the transmission, a little patience is all it took to get it out. use the calc and replace the gear. My car went from 3.08 to 3.45's and the speedo is spot on.
I am not sure if it will allow for going down to 3.9's which is not a factory gearing. In this case, you can go to some auto elec/car stereo place and there is an electronic speedo correction unit you can buy. It was a little too expensive and complicated for me since i could just change gears, but see how you go

I don't think the flash tuner will be able to adjust the actual speedo, but I do know it can (and should) be used to change the trans shift points. The other boys are right, the gears change relative to speed, not rpm.