1999 Sport 4.0 auto, 33" BFG Mud Tires, what speedo gear do I need. Speedo is off by about 7-8 MPH I think.
This chart should help you out once you find out your current gear ratio.
I have a 31 tooth and a 39 tooth brand new still in a bag. (Long story) If you need either of those two, I will ship either one to you for $40.
thanks guys, sorry it took so long! I checked twice, turned the wheel 2 times and axle turned just a fraction over 3 turns, so I'm guessing the stock 3.07 differential? The chart above doesn't list a gear for the 3.07/33" tire combo, do I just use the 26-tooth gear? And I'm seeing long and short gears, I assume it depends on transfer case? Not sure which one I have?
Look at the ratio tag bolted onto your axle's differential cover at its 9 o'clock position, it will tell you what ratio you have
This ratio tag is indicating a 3.73 axle ratio.
ha, I totally missed that tag! It's been painted over with flat back plus it was dirty. Yep, it's 3.07. So which speedo gear do I need, long or short one?
You need a short shaft speedometer gear. A 25 tooth is likely to be very close but it's not GPS verified. You really should regear, your TJ must be pretty low on performance with 33's and 3.07 axle gearing. 4.10 would be the correct axle ratio to regear to. Regearing will up the performance and mpg, your engine is lugging/running very inefficiently with 33's and 3.07 gears in your axles.
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Wait I’m no gearing guru here but wouldn’t 4.88 be way too steep for the 3-speed auto with the 4.0??
Good catch, I forgot he had the 3-speed automatic plus I had just come out of another similar thread where the engine was a 2.5 engine. No excuses though. 4.10 would be a good all-around highway trail ratio for 33's with that particular transmission and 4.0L engine. I'll correct my above 4.88 recommendation to 4.10.
Not for offroad use, posi's are more appropriate for slick road conditions.
Assuming the rear axle is a Dana 35, it's not strong enough for a locker. Though it could easily be made strong enough by installing a Super 35 kit from Revolution Gear which includes a choice of several lockers.
Hmm. I changed from 34 gear to 31 gear. I have the stock 3.73 diff with 33”.
The speedo now reads faster by 2-3mph faster than gps vs 34gear that reads 2-3mph slower than gps. Wondering if my diff is actually 3.73 when I got it a couple months ago.
The speedo now reads faster by 2-3mph faster than gps vs 34gear that reads 2-3mph slower than gps. Wondering if my diff is actually 3.73 when I got it a couple months ago.
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