Gear ratio and RPM

[NCguy]

I have a 94 ranger xlt with
AT
4.0
4x4
4.10 gears(previous owner said he installed)
5" suspension lift
33x12.50x15 tires and wheels
Ftr aussie locker
Not sure about diff gearing as I have not checked behind covers.
Going 65mph I am getting 1800 rpm's

Does that sound right for my set up?

 

[ericbphoto]

4.10 is your differential gear ratio

there are some charts and calculators in the tech library to help you figure out the rest if your question. Im having a busy day at work and can’t look it up for you right now.

 

[rusty ol ranger]

Auto or manual? We'll need to know to factor in the O/D gear

 

[ericbphoto]

Profile says auto. If it’s that truck.

 

[NCguy]

Auto or manual? We'll need to know to factor in the O/D gear

It's an AT with overdrive.

 

[19Walt93]

You could check the code on the door tag or even slide under there and look at the rear end tag.

 

[NCguy]

Previous owner said he installed 4.10 gears and aussie front locker....I just haven't checked.

 

[19Walt93]

I was going to say how treacherous it is to drive in snow with a front locker/limited slip until I noticed where you are. Never mind.

 

[RonD]

No, it looks like you have 3.73 ratio axles

You can go here: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

try ratio 4.10
Tires are 33
RPMs 1800
1994 A4LD uses .75 ratio OD(4th)

Comes up as 57/58 MPH

using 3.73 as axle ratio comes up as 63 MPH << so that's most likely what you have


You can also jack up the rear so tires are off the ground, Block front tires and put trans in Neutral
Mark tires on the inside, and mark drive shaft
Rotate drive shaft and watch tires
Drive shaft should rotate 3 and 3/4 turns for 1 full rotation of a tire if its 3.73
Just over 4 turns would be a 4.10

With tires still off the ground, turn one tire and watch the other, if it turns the same direction you are turning then its a Limited Slip axle, if it turns in the opposite direction its an OPEN axle

 

[Shran]

Speedometer reading correctly?

FWIW tires vary greatly in actual height... a 33 is almost never a 33, it could be, but usually they are actually smaller. I have some 31" Duratracs on 15x7 wheels that are only 1/2" taller than my set of 30" BFGs that are on 15x8's. For a while it was common to get Interco tires that were off by inches - for example 36's would measure out to 34" or under.... get an actual measurement on tire height and run that through the calculator.

 

[RonD]

+1 ^^^

Forgot about the speedometer error, check speedometer accuracy first with mile markers or GPS APP on your phone

 

[NCguy]

You could check the code on the door tag or even slide under there and look at the rear end tag.

No, it looks like you have 3.73 ratio axles

You can go here: https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

try ratio 4.10
Tires are 33
RPMs 1800
1994 A4LD uses .75 ratio OD(4th)

Comes up as 57/58 MPH

using 3.73 as axle ratio comes up as 63 MPH << so that's most likely what you have


You can also jack up the rear so tires are off the ground, Block front tires and put trans in Neutral
Mark tires on the inside, and mark drive shaft
Rotate drive shaft and watch tires
Drive shaft should rotate 3 and 3/4 turns for 1 full rotation of a tire if its 3.73
Just over 4 turns would be a 4.10

With tires still off the ground, turn one tire and watch the other, if it turns the same direction you are turning then its a Limited Slip axle, if it turns in the opposite direction its an OPEN axle

Speedometer reading correctly?

FWIW tires vary greatly in actual height... a 33 is almost never a 33, it could be, but usually they are actually smaller. I have some 31" Duratracs on 15x7 wheels that are only 1/2" taller than my set of 30" BFGs that are on 15x8's. For a while it was common to get Interco tires that were off by inches - for example 36's would measure out to 34" or under.... get an actual measurement on tire height and run that through the calculator.

Door tag says 91 which I believe is an open 8.8 3.27. Rear axle has what looks like factory disc brakes so maybe it was an axle swap? Tires are 33's but tread is only 1/4" frt. And 3/16 rear. As far as speedo I'm just guessing. I installed speed ap on phone as suggested and will update.

 

[RonD]

Thing about 4x4s is you have to have the same ratios front and rear, of course

Disc brakes did come on Explorer axles, and they did have 3.27 option

3.27 ratio at 1,800 RPM would be actual 72 MPH, and if speedo is not correct then it might show 65 MPH with the 33" tires
Stock 29" tires would show 64 MPH

 

[Shran]

Measure your tire height from the ground to the top of the tire, use that measurement.

Definitely did not have disc brakes in the rear from the factory - probably was swapped in from an Explorer. Cool! That's a nice bonus.

If you don't have tags on the axles, you can pull the cover and count teeth on the ring & pinion, then divide the larger number by the smaller number... for example 41 ring gear teeth and 11 pinion = 3.73, 41 and 10 = 4.10 and so forth... the ring may even be stamped with the ratio. Dana gears usually are stamped with something like "41 11", not sure about Ford gears. Probably wouldn't hurt to take a look inside anyway given the sad state of your front end.

 

[ericbphoto]

Counting teeth or reading markings on the actual gears is the most accurate. You can be pretty sure by putting the axle up on Jack stands and with the transmission in neutral, turn the pinion gear by hand. Mark a tire with chalk. Count how many times you rotate the pinion to make one full tire rotation. About 3 1/4 rotations would be 3.27 ratio. About 3 3/4 turns would be 3.73. Just over 4 rotations would be 4.10. Etc.