Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Welcome to the new NAXJA Forum!
If your password does not work, please use "Forgot your password?" link on the log-in page.
Please feel free to reach out to [email protected] if we can provide any assistance.
truely not sure why everyone says our stock breaks are inadequate, i could lock up 33s on my other xj no problem. my xj now cant lock em up now due to abs. i think everyone is too used to brakes on our new cars that u barely push the damn things and almost get whiplash if your not expecting the sensativity. its understandable that xj's are older tech and dont have great brakes but they work just fine. if my yota was able to lock up 37s on factory brakes then i gaurantee my jeeps brakes are just as safe with 33s
My jeep is the newest vehicle I've owned, I'm not used to driving new cars, I have driven many cars from VW jettas to a CTS. My jeep has the worst brakes of nearly all of them. My buddy's accord which is OLDER than my jeep has far better brakes and stock is only 300 pounds lighter. Brakes on XJ's suck, that's all there is to it. Once I swap rear axles in hoping for better performance with discs.
My jeep is the newest vehicle I've owned, I'm not used to driving new cars, I have driven many cars from VW jettas to a CTS. My jeep has the worst brakes of nearly all of them. My buddy's accord which is OLDER than my jeep has far better brakes and stock is only 300 pounds lighter. Brakes on XJ's suck, that's all there is to it. Once I swap rear axles in hoping for better performance with discs.
Dunno, I can lock up my 33s no problem with stock brakes. I generally don't, you stop faster if the tires don't slide, so aim for braking hard enough to hear them almost start to slide and no harder.
I just left 31's and 3.55 on 4.0L and AW4. I hated it.
The math straight up says that 4.10 will be the same as stock and 3.55's however when you start building you add weight and the rolling mass of the tires soaks up a lot of power.
If you have any hills in your area, ever tow, go at least 1 step deeper to 4.56 at 31's.
I even went 2 steps deeper to 31's and 4.88s I love it I still cruise at 67-70 MPH and have some extra "GRUNT" for when I really need it.
the auto trans uses 2 variables to make a decision, 1 is the throttle body sensor, the other is the vehicle speed sensor.
put on bigger tyres and you will 'lie' to the transmission computer.
2 fixes!
first, alter the other variable (tps)the other way to get your shift points back (not recommended as the signals from the tps are ALSO used for the engine computer and could foul that up!)
second, by a replacement speedo cog with a different ratio that brings back the correct speed readings (both for you and your transmission).
i have also crimped 1 centimerer (1/2 inch) more tension into the throttle cable that goes to the transmission (its not called a kickdown cable in this car, it only varies line pressure with throttle plus a detent as well). its now much firmer and shifts more positavely. lower trans temps too
with 400lb of water and gear i managed to claw back a couple of litres per hundred (i think from 14mpg to 18 or so, not sure, bad at maths!). i don't know how increasing line pressure will make the lockup torque converter use less fuel? logic would dictate the opposite?
these mods make the trans more of a utility shift quality (good for loads and trail) rather than Ultra smooth passenger shift quality.
but if you have lifted your fourby, i don't think you will mind......:yap:
Things the TCU uses to make its decisions:
* brake pedal (used in torque converter lockup decisions)
* NSS (torque converter lockup decisions, also solenoid settings I believe, and on 98+ also probably prevents throwing a code when the TCU detects the transmission is not in the gear it requested)
* output speed sensor
* input speed sensor, on 98 and later vehicles
* TPS
The VSS is used by the ECU (cruise control, fuel trims, signals to IP on 97+) and dash cluster (97+) and nothing else.
When using the gear ratio calculators, don't forget to adjust for the 25% overdrive you have with the AW4. Some of the calculators forget this and it's kinda important!
I have ~250 break in miles on 4:56 gears on 31x10:50s. With a 41 tooth gear the speedo is reading about 1.5 mph fast vs GPS at 55 mph.
Engine rpms are ~2250 at 55/60mph. Should be ~2600+ when we get to AZ and run 75+ mph. Just where we want it. From what I have read, the 4.0 likes to turn and the 2600 r's should be close to the "sweet spot" for power and gas mileage.
With the prior stock 3:55 gears the 31's were too much. Lugging all the time and lot's of shifting on highway hills.
Well.. I just wanted to check all of the RPM assumptions and assertions myself. I used the actual tire diameters, both old and new. The 3.9s actually provide the exact match for engine RPM, and is roughly 9% 'easier' on the engine than the current configuration. The 4.11s would provide an additional 5% increase in RPMs over the factory configuration - a nice torque boost but not over revving.
I included my equations for review, pretty sure they are correct.
Code:
| Factory | Current | Best RPM Match | One Up
-----------------------------------------------------------------------------------------
MPH | 60.00 75.00 | 60.00 75.00 | 60.00 75.00 | 60.00 75.00
Gear Ratio | 3.55 3.55 | 3.55 3.55 | 3.90 3.90 | 4.11 4.11
Tire Diameter | 27.50 27.50 | 30.25 30.25 | 30.25 30.25 | 30.25 30.25
RPM | 2603.52 3254.40 | 2366.84 2958.55 | 2603.52 3254.40 | 2740.20 3425.25
RPM /1:.75 OD | 1952.64 2440.80 | 1775.13 2218.91 | 1952.64 2440.80 | 2055.15 2568.93
Equations
Feet in a Mile = 5280
Vehicle Feet per Minute = (MPH / 60 minutes) * Feet in a Mile
Wheel Rotations per Minute = (Target RPM / Gear Ratio)
Tire Circumference in Feet = (Tire Diameter inches * PI / 12 inches)
MPH = (Wheel Rotations per Minute * Tire Circumference in Feet) /
Feet in a Mile * 60 Minutes
Gear Ratio = Target RPM / (MPH / Tire Circumference in Feet)
Tire Diameter = ((Vehicle Feet per Minute / Wheel Rotations per Minute) *
12 Inches ) / PI
RPM = (Vehicle Feet per Minute / Tire Circumference in Feet) *
Gear Ratio
Well.. I just wanted to check all of the RPM assumptions and assertions myself. I used the actual tire diameters, both old and new. The 3.9s actually provide the exact match for engine RPM, and is roughly 9% 'easier' on the engine than the current configuration. The 4.11s would provide an additional 5% increase in RPMs over the factory configuration - a nice torque boost but not over revving.
I included my equations for review, pretty sure they are correct.
