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Stock 4.10 gears ????

R

Rod Knee

NAXJA Forum User
Location
Grand Jct., CO
I have an AW4 transmission, NP242 TC, dana 30 front, c8.25 27 spline rear, nominally 31 inch general grabbers but actual diameter closer to 29 inches. Using the gear ratio charts linked below inputing either 29 or 31 inch tires, I get rpm's that match a 4.10 gear ratio rather than a 3.55. Just wondering if anyone else had noticed a calibration problem of this nature with regard to these charts. Alternatively wondering if anyone had ever heard or any "96 XJ's (production in Fall of "95) with auto that came out of factory with 4.10's rather than 3.55's.

I've worked the grimjeeper program back and forth several times and keep getting a match for the 4.10's. In D my cherokee goes 75 mph spinning 2500 rpm, 65 mph at 2300 rpm, and 55 mph at 1900 rpm. Speed determined by GPS, btw......

http://www.naxja.org/forum/archive/index.php/t-1032714.html
http://www.grimmjeeper.com/gears.html
 
Get under and check the axle tags, but I was under the impression that 4.10 only came in 4 Banger xjs... even the tow model 4.0 only had 3.73
 
Read the stamping on the ring gear, or jack up the axle and spin a tire while counting drive shaft revolutions.
 
Yeah just look at the stamp on the gears, divide the big number by the small number and you'll know for sure... I think those charts are just estimates everybody's Jeeps are different

Edit: also if the tags are gone they could be aftermarket setups
 
I did the jack up the back end and compare rotations of the tire and driveshaft test a few years ago and concluded I had 3.55. Looking at yet another chart (link) though I get 4.10's as best match again. Either I have 4.10's or all these charts are not calibrated for the auto XJ very well. I wish I had looked at those ring gear stampings last time I had a diff opened up.

Can anyone report some rpm's for 65 mph and 75 mph with the 3.55 and/or 4.10 on nominal 31 inch tires?

http://www.naxja.net/forum/showthread.php?p=244753482
 
For tire diameter, go to the MFGs tire website and look up your tire. Many 31" tires are around 30.5"

As for gear/tire/RPM Charts. They are generally calibrated at 65 in a 1:1 gear.
On an XJ, the 1:1 gear is 3rd, not "D". "D" gets you into OD (a .75 OD on an Auto).

Using the Gear/Tire chart at 4Wheel Parts I get 2584 for 30" of Tire @ 65mph in 1:1 gear.

With an auto you will get some slippage that factors in. To measure without the TC getting involved, make sure the surface is level and apply only as much gas as it takes to maintain speed (feather touch).

It is possible that someone changed out the axles from a 2.5L, but I would verify the numbers first before jumping to conclusions. As per above, it is not hard to find out the gear ratio by jacking up the back, dropping the DS, and finding out how many times the yoke needs to turn to get the wheel to perform 1 rotation.

-Ron
 
Tire size plays a huge role in the RPM differences. If you say you have 31's, and they measure out to 29", well that's an inch of radius you're missing. Compare that to someone who has 31's, but they really measure a true 32", and you guys are gonna have different RPM ranges at a constant speed.

I have 255/75/17 sized tires. 4 are Treadwright, and my spare is Goodyear. The 4 tires measure exactly 32", and the spare measures exactly 31" in diameter. All have the same labeled size.......
 
Probably worth noting that measuring from the ground to the center of the hub and then multiplying times 2 is the best measure of effective diameter. This is what I did. Measuring across horizontally will probably yield a different result for the same tire.

Like I said above, even using 29 inches as my diameter my rpm's for specific speeds match up with 4.10 gears on all the charts I've linked to. I acknowledge it could be a problem with the charts.

Thanks Ian for your numbers.
 
Last edited:
If you changed tire size, and didnt change the speedo gear, this could cause your numbers to be off. You wont be getting a true speed value with larger tires than stock. Not sure how this works into your formula, but it is something that should be considered.
 
I am not sure if this could help. Tires are BFG AT's 30 X 9.5 X 15. All speeds are also GPS verified while using cruise control on I-75 in South Florida where it is perfectly flat and goes East to West across Aligator Alley.

April 10, 2008

RPM’s at 55 MPH with 4.10:1 gears running 30” tires 1980
RPM’s at 60 MPH with 4.10:1 gears running 30” tires 2175
RPM’s at 65 MPH with 4.10:1 gears running 30” tires 2360
RPM’s at 70 MPH with 4.10:1 gears running 30” tires 2550
RPM’s at 75 MPH with 4.10:1 gears running 30” tires 2700
RPM’s at 80 MPH with 4.10:1 gears running 30” tires 2920
 
Rod Knee said:
Techno your numbers do help. Your rpm's are high for your gear ratio and tire setup relative to the grimmjeeper chart, just like mine are...........
Click to expand...

Yes, they are. Even with the 3.55 ratio, they were about 100 +/- above what the charts indicate they should be. I intend to go to 31" tires so that should reduce the RPM and increase the MPH a bit.
 
I know this has been asked a million times and yes i have researched the question but i still havent came up with a definitive answer. What years did they stop using stock 4.10 gears? So far all ive been able to find is "older 4bangers" basically i plan on pullin an 8.8 with 4.10 from a explorer and dont want to spend 600-1000 to regear the dana 30. Its a 93 and i dont really want the crappy older dana 30s. What should i be lookin for and is it worth it to pull a axle or just regear?
 
There is nothing wrong with the older D30's. Around here, factory 4.10 axles are almost as rare as XJ Dana 44 rear axles.

4.10 gears were optional for all model years when combined with the 4 cylinder engine.

A good used axle is cheaper than re-gearing.
 
Tim_MN said:
4.10 gears were optional for all model years when combined with the 4 cylinder engine.
Click to expand...
My project axle came from a '96, with 4.10 gears, verified.

The only caveat to the "4-cylinder, 5-speed" indicator is that the vehicle may actually have 3.73 gears.
 
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