98 ranger axel swap question

[pwrranger88]

Ok so i recently bought a 98 ranger and want to replace the rear axle which currently has 3.55s with a rear out an explorer with 4.10. My question is will i need to have my speedometer recalibrated or will it be fine?

 

[Captain Ledd]

Any time you change the gear ratio or substantially change the tire size, the speedometer will need to be re-calibrated.

Though (and I did this for a while), you can follow a trustworthy friend around with a bone stock vehicle at various speeds and write down what speed they're travelling at and what shows on your speedometer, and tape it to your dashboard.

Hokey I know LOL, but it works in the meantime. If you have a manual trans you can do Speed = gear : RPM.

(hopefully this lines up)

____ 3rd- - -4th- - -5th
25---2500---2000
40---3500---2900
70-----------3500---2600

Something like that^ I know the numbers are unrealistic, it's just an example of the chart.

 

[4x4junkie]

On a '98, the speedometer is sensed off the rear ABS sensor. I'm pretty sure changing the gear ratio will not change the speedo reading as long as the tone ring is the same (or has same number of teeth).

If you change tire sizes however, then yes this will require recalibrating the speedo.

 

[don4331]

Riddle me this:

I swapped a '99 rear end into my '98, going from 3.73s to 4:10s - which if tone ring is same; should have made no difference.

I also changed from 235/75R15s (28.9") to 31x10.5R15s. '99 had 245/75R16s under it - which are as close to identical in diameter to the 31x10.5R15s as one can get (30.7" versus 30.5"). So, I should be going 6% fast...

I did not re-calibrate the speedo, but cop next door has checked my speed against his gun and numbers matched. Which surprised me as I though numbers would be low - gearing was bigger change than tires but I was thinking transfer case pick up, not differential.

I liked your original explanation: Different tone rings makes no sense when you can program in the ratios/tires.

This leaves me confused/concerned - running 10 over limit, I probably get away with; 17...not so likely.

 

[Captain Ledd]

On a '98, the speedometer is sensed off the rear ABS sensor. I'm pretty sure changing the gear ratio will not change the speedo reading as long as the tone ring is the same (or has same number of teeth).

If you change tire sizes however, then yes this will require recalibrating the speedo.

Oh that's right! I spend too much time with the older trucks.

I believe 4x4Junkie is correct, ignore my previous post.

 

[4x4junkie]

Riddle me this:

I swapped a '99 rear end into my '98, going from 3.73s to 4:10s - which if tone ring is same; should have made no difference.

I also changed from 235/75R15s (28.9") to 31x10.5R15s. '99 had 245/75R16s under it - which are as close to identical in diameter to the 31x10.5R15s as one can get (30.7" versus 30.5"). So, I should be going 6% fast...

I did not re-calibrate the speedo, but cop next door has checked my speed against his gun and numbers matched. Which surprised me as I though numbers would be low - gearing was bigger change than tires but I was thinking transfer case pick up, not differential.

I liked your original explanation: Different tone rings makes no sense when you can program in the ratios/tires.

This leaves me confused/concerned - running 10 over limit, I probably get away with; 17...not so likely.

I've noticed that most speedometers generally seem to be calibrated about 3-4% fast from the factory. So most likely what happened is the bigger tire size simply compensated for this small calibration error (the small overshoot (in theory anyway) probably wasn't enough to be easily detectable, especially if your 31s have worn in a slight bit from when they were new).