how accurate is a speedometer

[schmidlkofer]

ok so after you get bigger tires and different gears how do you calibrate the speedometer so its accurate?what needs to be done? what do other people do?

 

[cloaked_chaos]

You need to change the gear on the speed sensor. Use equations to figure out which one you need.

 

[schmidlkofer]

oh dang..numbers...ok thanks. ill use a gps in the mean time.

 

[schmidlkofer]

You need to change the gear on the speed sensor. Use equations to figure out which one you need.

is that in the transmission?and do i need to take the transmission apart to do it?

 

[FROADER]

What gears were stock in your truck, and what gears and tires do you have/want?

Axle codes on the inside door panel

41 - 3.27 non-limited slip (Explorer/Mountaineer)
45 - 3.55 non-limited slip (Explorer/Mountaineer)
46 - 3.73 non-limited slip (Explorer/Mountaineer)
42 - 4.10 non-limited slip (Explorer/Mountaineer)
D1 - 3.27 limited slip (Explorer/Mountaineer)
D4 - 3.73 limited slip (Explorer/Mountaineer)
D2 - 4.10 limited slip (Explorer/Mountaineer)

 

[schmidlkofer]

ill find out sunday when i ibuy the explorer....i know it has some 36 inch tires but i dont know about the gearing...i know it has been changed tho.

 

[FROADER]

Oh, is it from this site?

 

[cloaked_chaos]

Is it 2wd or 4wd?

 

[schmidlkofer]

im buying the explorer from a guy in the town i live in he owns a bar and is hard to get a hold of. i live in enid oklahoma and its 4wd....with 36 inch tires. what should i do to it? its pretty stock besides gears lift and tires.and cold air intake and exhaust.

 

[cloaked_chaos]

See the top right of the picture (grabbed from the 4x4 shift motor rebuild thread)

 

[pope_face]

Just to get this straight, all that needs to be done to get the speedo to the proper speed is to replace the gear for the speedo cable? Also... maybe I'm a complete idiot here, but it's the differential that affects the gearing, correct? Would the shop that sells the differential/locker/etc sell the appropriate speedo gear as well? Or, if I were to get a differential from a different RBV (or go full-size), would I be able to get a speedo gear from the dealership or Junkers, providing it came off an RBV with the equivilant gear ratio?

Then again, this is assuming stock size tires, and that's not what this thread is about... Is there a certain method for selecting the appropriate speedo gear based on gear ratios and tire size?

 

[cloaked_chaos]

Just to get this straight, all that needs to be done to get the speedo to the proper speed is to replace the gear for the speedo cable?

Yes, in most cases where damaged parts are not a factor.

it's the differential that affects the gearing, correct? Would the shop that sells the differential/locker/etc sell the appropriate speedo gear as well? Or, if I were to get a differential from a different RBV (or go full-size), would I be able to get a speedo gear from the dealership or Junkers, providing it came off an RBV with the equivilant gear ratio?

You make it sound a lot more difficult than it actually is. It is just a little plastic gear that is easily changeable.

Then again, this is assuming stock size tires, and that's not what this thread is about... Is there a certain method for selecting the appropriate speedo gear based on gear ratios and tire size?

It is possible to use formulas to figure out which gear you need, based on your diff gearing and tire size, but it is so much easier to just figure out the percentage your speedo is reading off of normal, and then select the appropriate gear with the same percentage difference in tooth count. It wont be exact, but just choose which one is closest to actual percentage. Remember that as your tires wear down, your speedo will read slightly faster.

 

[cloaked_chaos]

This is a picture I edited to show what it looks like. This one happened to have the black 20 tooth gear because the car has 33"s with 4.56 gearing. In contrast, the stock 235 tires with 3.73 gearing would use a 19 tooth gear.

 

[mikeh44]

ford is not like chevy chevy has about 20 different gears for the speedo ford i believe they only have three maybe four gears for the speedo but you can go to a speedometer shop and have them build you a correction box

 

[schmidlkofer]

ford is not like chevy chevy has about 20 different gears for the speedo ford i believe they only have three maybe four gears for the speedo but you can go to a speedometer shop and have them build you a correction box

cool cool thanks.