Speedo gear tooth count verification

Alright, I know this is a subject covered a good number of times on here. I have searched and read most of those post including ones on other forums.

However from the various speedo gear charts floating around I have read that I need both a 38 and a 40 tooth count gear. So looking for advice, perhaps from someone with the same set up on which is more accurate. Or if I should just say screw it and shoot for the middle with a 39. Thanks.

Went from stock to, 4.10 with 30" AT (3.55 stock with 30" was reading 2 mph slow, now with 4.10 it reads 8 mph fast at GPS indicated 60 mph) Thanks

Also where is the cheapest place to get these gears? The local dealers want $80 a piece and I see them on Quadratec for $40 plus $10 shipping.

I used the chart at Go Jeeps website. It was accurate for my 4.10 gears and 31 inch tires. Link: http://www.go.jeep-xj.info/HowtoSpeedoGears.htm It says you need a 38. My speedo is off by 1/2 MPH GPS verified at 60 MPH after using Go Jeeps chart.

Or take the existing gear out of the transferbox and see how many teeth your current gear has and multiply by 1.133 Your speedo is off by 13.3%. 68 MPH indicated divided by 60 MPH actual equals 1.133.

I would guess you might have a 34 tooth gear but you need to check before doing the math. If you have a 34 tooth then 34 times 1.133 would equal 38.5 tooth gear. You could round up or down to a 38 or 39 tooth gear.

Your math, your call.

I got my gear with a new O ring (both Crown replacements, probably what you'll get most places) for about $45 shipped, IIRC, off a seller on ebay.

Thanks for the replies, I appreciate it.

I might have one in my tool box that I can make a deal with you on.


Tapatalky

Well I finally got around to switching out to a 38 tooth gear tonight. After taking it for a 10mi loop I found that it seems spot on at 60mph, and the odometer showed it being off by 1% on total mileage, compared to my Garmin GPS. Needless to say I am pleased. Thanks for the info.

For any future reference I am running 98' 4.0, AW4, 4.10 gears, 30x9.5 Goodyear Wrangler Silent Armor AT and now a 38 tooth speedo gear.

Glad it worked out.