Does anyone know if anything has to be done to the Speedo after changing the axle gears?

I'm hoping that the speedo gets its info from the ABS sensor ring in the rear diff. In which case, it won't make any difference.

Thanks.

 

i have a 2001 V-6, 8 1/4 rear end came from the factory with a 3.5 gear had it changed to 4.1. my truck and others have tires that are bigger than what is on the door. i went to a good trans shop and they put there computer on my truck computer, and was told that the truck computer was set fore the tires that are on the truck. NO need to recalebrate the speedo. I THINK the factory didnt have the right size tire and used a bigger tire AND recalaberated the computer at the factory. there is the what i think. the rear end gear has a plate bolted to the ring gear that is used to tell the computer the speed, that is TOTALLY different way than older trans/rear ends. meaning changing the ring gear will not change the speedo, BUT changing the tire will.

 

your spedo will be off. I went with smaller tires and the local dealer charged me 40bucks to recalibrate the spedi.

 

Thanks guys.

I found the answer over on the Ram section.

Everyone seems to agree that a Gear swap DOESN'T effect the speedo because it takes its reading off the ABS ring on the carrier.

Changing Tyre sizes DOES effect the Speedo.

My old SuperChips programmer could do this. Sadly the SCT programmer doesn't have this facility built in, although I'm sure it could be used to do it if given the right program.

Luckerly, I don't need to do this. I'm running 31's on mine and they have raised the gearing slightly but it means that my Speedo is actually 100% accurate when checked against my GPS, as from the factory *******ly all Speedos read slightly higher.

 

Don't know why the word "*******ly" got starred out!

 

Moe,
How much of a difference did the gear swap make? You've done the exact sam ratio swap that I'm doing!

 

You are right gears wont change speedo.

 

TO: DakinUK i changed from a 3.55 to a 4.1. and a posi. i don not drive on the hi way. what happened was that the trans started shifting sooner than it did before. now it sifts to overdrive at 35 to 40 mph, the speed that is what most of my driving is at. causing the rpm to be 1400 to1600 . my mpg went from 8-9 to 13 mpg. i drive HARD. BUT remember at hi way speeds you should loose mpg, but i dont know how much. but the power gain was about what i thought it would be. allso check out using marvel mystery oil added to the gasoline. it doesnt mean you will gain mpg with it, but your engine should start better, some think the engine will last longer, but no proof. i was wanting more power, it came out very good, iam very happy.