speedo gears

[Destroyer000]

alright ive done me research and iam mind boggled. iam running a 33inch tire with 4.10s and my tcase has a white gear. by using the calculator in the library new teeth = old speedo gear x ( new axle ratio / old axle ratio).. so it would be 17x(4.10/3.27)= 20.8... so 21.. i went from 3.27s to 3.73s. to 4.10s. when you plug in 19x(4.10/3.73) you get 21.... so i put a 21 tooth in and my speedo seems to be way off. so right now i have a 20tooth in it and according to the mile markers s a tenth of a mile off. so for every hundred miles i have to add ten miles... you guys with 33s and 4.10s what are you running for a speedo gear?

 

[superds]

I'm too tired to do all the math. For a reference point, I believe I'm running a white gear with my 32" tires and 3.73 gears and my speedo reads 1-2 mph low around 30mph (about as close as I could get it with the available gears).

 

[LearjetMinako]

You forgot to calculate the change in tire sizes too. Changing the axle from a 3.27 to 4.10 would mean you need a larger (more teeth) speedo gear to slow down the speedo. Increasing the tire size would mean you would need a smaller speedo gear (less teeth) to speed up the speedo.

For starters, you need to know the orginal setup
Speedo gear = 17
Axle ratio = 3.27
Tire size = ?

New setup:
Speedo gear = (undetermined)
Axle ratio = 4.10
Tire size = 33"

Find the orginal tire size (should be on the driver's door jam) and then we can calculate your new speedo gear teeth number.

 

[Destroyer000]

You forgot to calculate the change in tire sizes too. Changing the axle from a 3.27 to 4.10 would mean you need a larger (more teeth) speedo gear to slow down the speedo. Increasing the tire size would mean you would need a smaller speedo gear (less teeth) to speed up the speedo.

For starters, you need to know the orginal setup
Speedo gear = 17
Axle ratio = 3.27
Tire size = ?

New setup:
Speedo gear = (undetermined)
Axle ratio = 4.10
Tire size = 33"

Find the orginal tire size (should be on the driver's door jam) and then we can calculate your new speedo gear teeth number.

ive done all that .. 17 tooth with 3.27s and 235s = 29 inch tires.. then i went to 19 tooth with 3.73s and 31s to 4.10s and 33s.... and iam running a 20tooth....

 

[Destroyer000]

ive done all that .. 17 tooth with 3.27s and 235s = 29 inch tires.. then i went to 19 tooth with 3.73s and 31s to 4.10s and 33s.... and iam running a 20tooth... it says i need a 21 but when i install it my speedo seems WAY off. like iam going way faster than i really am.. the 20 seems to be "close" hence why iam confuzzled.

 

[LearjetMinako]

ive done all that .. 17 tooth with 3.27s and 235s = 29 inch tires.. then i went to 19 tooth with 3.73s and 31s to 4.10s and 33s.... and iam running a 20tooth....

I have been running the math over and something doesn't seem right. So going off the fact that you are a 1/10 of a mile off on a 20 tooth with your current setup, try a 18 tooth to make up the difference.

 

[nall_one]

I'm sort of doing the same thing, except mine still has the original 3.27 and I'm running 31/10.50/15s. seems i have a white 17 tooth gear (well its sort of yellow now) in their, and its around 5 miles slow at 55. (going 60 instead of 55 like the speedo says) so it looks like i need a 15.5, or a 16 since 15's don't exist. everything seem right their? or am i doing something wrong?

also, since i have a white 17 instead of green, i would need the maroon 16 instead of the blue? i seem to remember reading somewhere because its a 4x4 and the gears in the transfer case i use manual trans VSS gears.

 

[nall_one]

still haven't got this thing swapped, anyone want to chime in? its a A4LD with 235 size stock, now 31/10.50's stock 3.27 rear. first of all anyone know what the stock gear is, I'm thinking its a 17 tooth, but i could be wrong. i think i may have poped it out and couted 17, but i cant remember, been a while... whatever it is though, seems i need to loose a few teeth to speed up the speedometer. kind of want to get this fixed since i hear this thing somewhat controls shift points. i do seem to remember it having a wire hooked to it as well as the cable.

 

[Captain Ledd]

Drive gear teeth (the gear on the output shaft) X Axle Ratio X Tire revolutions per mile

Divide that number by 1001

This will be the driven (the one that's REAL easy to change) gear tooth number.


EDIT:

Tire revolutions per mile:

20168 (divided by) "Tire diameter in inches".

 

[85_Ranger4x4]

Drive gear teeth (the gear on the output shaft) X Axle Ratio X Tire revolutions per mile

Divide that number by 1001

This will be the driven (the one that's REAL easy to change) gear tooth number.


EDIT:

Tire revolutions per mile:

20168 (divided by) "Tire diameter in inches".

That is what I did, once you find out how many teeth the drive gear has it is pretty easy. Since my tires were fairly new I went on tirerack and got the revs per mile from there.

http://www.therangerstation.com/forums/showthread.php?t=113620&highlight=speedo

 

[straycat]

still haven't got this thing swapped, anyone want to chime in? its a A4LD with 235 size stock, now 31/10.50's stock 3.27 rear. first of all anyone know what the stock gear is, I'm thinking its a 17 tooth, but i could be wrong. i think i may have poped it out and couted 17, but i cant remember, been a while... whatever it is though, seems i need to loose a few teeth to speed up the speedometer. kind of want to get this fixed since i hear this thing somewhat controls shift points. i do seem to remember it having a wire hooked to it as well as the cable.

Just do what I did. I went to my 4x4 shop and they installed the correct gear for my 33's and 4:10. I bought my tires from them and it cost me $30 for them to reset it for me. No big deal. My speedo is perfect everytime I check it with one of those digital check your speed limit gizmos!! I hit 40 mph and it shows 40, I hit 70 and it shows I am doing 70. Problem resolved.

 

[85_Ranger4x4]

Just do what I did. I went to my 4x4 shop and they installed the correct gear for my 33's and 4:10. I bought my tires from them and it cost me $30 for them to reset it for me. No big deal. My speedo is perfect everytime I check it with one of those digital check your speed limit gizmos!! I hit 40 mph and it shows 40, I hit 70 and it shows I am doing 70. Problem resolved.

It isn't that hard to do a little math and poke the $15 gear in there yourself, it is just a bolt and a clip to swap them out.

They are rarely perfect because the gears available skip tooth counts. I figured up I needed a 15 tooth gear and as close as I could get was a 16 so I doubt it is dead nuts right... but it is a lot closer than it was with the original gear

 

[straycat]

It isn't that hard to do a little math and poke the $15 gear in there yourself, it is just a bolt and a clip to swap them out.

They are rarely perfect because the gears available skip tooth counts. I figured up I needed a 15 tooth gear and as close as I could get was a 16 so I doubt it is dead nuts right... but it is a lot closer than it was with the original gear

Hmmm, why do I keep hearing people trying to figure this out and buying the wrong parts and going back and forth with this? Just have somebody who does this for a living do it for you. It is a one time deal. It was worth the $30 to have it done right the first time!!

 

[85_Ranger4x4]

Hmmm, why do I keep hearing people trying to figure this out and buying the wrong parts and going back and forth with this? Just have somebody who does this for a living do it for you. It is a one time deal. It was worth the $30 to have it done right the first time!!

Because they suck at math?

The hardest part of it for me was figuring the number of teeth on the drive gear, because for some reason nobody publishes what color is what for that on the net. Afther that though it was cake. Pop the gear out and with a flashlight look in the hole and note what color the drive gear is. Go to the thread I posted earlier and notice which gear has how many teeth and enter that into the formula.

I have it in a spreadsheet, if you post up the driven gear (the one in your t-case/transmission) and tire diameter it would spit out the tooth count really quick.

One $15 gear that I bundled with a new camera to score free freight and I was done.

 

[straycat]

Because they suck at math?

The hardest part of it for me was figuring the number of teeth on the drive gear, because for some reason nobody publishes what color is what for that on the net. Afther that though it was cake. Pop the gear out and with a flashlight look in the hole and note what color the drive gear is. Go to the thread I posted earlier and notice which gear has how many teeth and enter that into the formula.

I have it in a spreadsheet, if you post up the driven gear (the one in your t-case/transmission) and tire diameter it would spit out the tooth count really quick.

One $15 gear that I bundled with a new camera to score free freight and I was done.

Yes, lol, they suck at math. While I got my new tires mounted and balanced they installed my spedo gear and I did not have to do anything. It was just worth it to me since I was there and when I took that Ranger home I knew my spedo was correct. That was back in 2000 after I lifted it. I am on my second set of 33's and the spedo is still perfect...unless I change out to a taller or shorter tire that is...lol