speedo calibration question

[fifty]

Hey all. My truck has the IDM mod, a PHP 6 Pos chip etc done. I recently went to 37's and am having 4.88 gears thrown in this week (orginally a dually with 4.10's and I guess 31.5 inch stock tires)

I have a strange feeling I am going to need to recalibrate the speedo

My buddy works at a ford dealership. Can he just plug his computer gizmo into the computer and calibrate it? Will it mess with the chip? Or must I get one of those inline computer speedo calibrator fooler things?

Thanks for the help! Oh and BTW its a 2002 F-350

[NoRalPh]

When I changed tire size, I used my AutoEnginuity to recalibrate the speedo. It worked pretty well but, you're going to change axle ratio too? That might take some figurin'

Maybe the Ford tool is easier to calculate the change, I just went by the diameter. I don't think your chip would be effected though (unless the Ford tool totally reloads the PCM while doing it)

[ZMANN]

Not 100% sure on the d80 but I imagine it's the same ( you can look for the sender on the dif ) but the SRW ford have the speed sensor in the rear dif and it is unaffected by gear changes only tire size changes because it reads rpms after the gears
so it makes Math a non issue thank god

[NoRalPh]

Originally Posted by ZMANN

Not 100% sure on the d80 but I imagine it's the same ( you can look for the sender on the dif ) but the SRW ford have the speed sensor in the rear dif and it is unaffected by gear changes only tire size changes because it reads rpms after the gears
so it makes Math a non issue thank god

GOOD POINT! I never thought about that... It would be a different story than if it were in the tailshaft of the trans - wouldn't it?

Yea! so Bonus! That does make it simpler.

[ZMANN]

Yes that is correct since those read before the gears

[fifty]

Yep! the sensor is in the diff. My main concern is with the PHP chip. Will it be effected if my buddy with the ford computer plugs it in the obd 2 port and adjusts the speedo? Or will I be fine?

[ZMANN]

I do mine with My A/E it has no effect on my programming I can't see accessing that module having any side effect to your chip sine it doesn't use the module anyways I would imagine your fine ,, people have to have done this plenty of times

[fifty]

cool, zmann, you wouldnt happen to be in cal would you? Well it was worth a shot!

[ZMANN]

No
but shout out to your local chapter it's a common tool

[fifty]

Ha! Has to try! I did put a shout out. Seems to be rare in these parts.