Speedometer gears are wrong

[Eberdt123]

My jeep seems to be about 10mph under what is shown on the speedometer. The guy I bought the jeep from said he just lived with it but since I am a new driver and want to be aware of my car and how it functions as well as the speed it is going, I want to ensure the speedometer is correct. The jeep has a total of 8" of lift with 33" tires. I have no idea what to buy or where to check for a good price to fix this problem. Any suggestions?

 

[MutantNinjaTJ]

Quadrasuck sells "corrective" speedo gears for about 25 bucks, you will need a 39 if memory serves me. Buy the o-ring as well. it's an easy install into the transfer case.

 

[Tangerined]

https://www.quadratec.com/c/reference/jeep-speedometer-gear-tooth-chart
You need to know the gear ratio in your diffs as well

 

[Eberdt123]

https://www.quadratec.com/c/reference/jeep-speedometer-gear-tooth-chart
You need to know the gear ratio in your diffs as well

How would I find that? If there is a way?

 

[Viking Jeeper]

My jeep seems to be about 10mph under what is shown on the speedometer. The guy I bought the jeep from said he just lived with it but since I am a new driver and want to be aware of my car and how it functions as well as the speed it is going, I want to ensure the speedometer is correct. The jeep has a total of 8" of lift with 33" tires. I have no idea what to buy or where to check for a good price to fix this problem. Any suggestions?

10 MPH at what speed? When going with different size tires the speedometer will be off a fixed PERCENTAGE of speed but never a fixed MPH. Does it read 2 MPH when doing 12 MPH? I doubt it. It will be a percentage off. Lift has nothing to do with it. If you have 33's you are in the neighborhood of 10% faster than the speedometer shows, if stock otherwise. Yes, as a young driver you should have it fixed so your mind is not calibrated wrong with regards to speed.

 

[Tangerined]

How would I find that? If there is a way?

If it's stock and hasn't been regeared, there should be a metal label bolted to your diff covers. If it's been regeared or the label is missing then you can jack up the Jeep and rotate the tires by hand and count the number of rotations vs drive shaft.

Can also guess at it, see what RPM you're at a known speed and plug it into this website:

http://www.grimmjeeper.com/gears.html

 

[Jerry Bransford]

Look at the 9 o'clock position on either of your two axle differential covers, there should be a metal tag bolted between two bolts that will have the axle ratio embossed into it.

This tag is indicating the axle has 3.73 gears inside.

 

[Eberdt123]

Thank you all for your help and it happens more in upper gears but yes you are correct about the 2mph vs the 12mph. I just need to get up under there and take a look. Maybe take an educated guess at what I have. But again thank you!