I put 31's on and now when I tow my trailer, 6 x 10, the transmission is constantly shifting. More than it did with a smaller tire. I understand why it is doing it but I wonder if anyone has a solution. Short of putting on the smaller tires. Can I reprogram shift points? Can I put the taller tire size in the computer and have it compensate? Thanks,

 

Sounds like you need a lower gear ratio. I'd say something like 4.10's. I run 31's with my stock 3.55's and its fine, but since you tow it sounds like you could use the gears.

 

Gears. I put 32's with a 4.5" lift on mine with 3.55's. It ran down the highway ok but my 6x12 trailer killed it. So much that I couldn't drive it on the highway. 4.56's fixed that along with giving me 4 mpg back on the highway.

 

Yes you need to re-gear to at least a set of 4.10's, they will bring you back to where you were before with the smaller tires. If you pull a trailer a lot might consider 4.56's or if you plan on a taller tire later on.

When you do change gears you will need to install a new speedometer gear for everything to read correctly.

 

Thanks for the advice.

 

I was going to add it certainly will help the trans and the engine. My trans overheated with the stock 3.55 with both the 31's and more so with the 33's. The constant shifting is hard on both and fuel mileage when I changed to the 4.56's my mileage increased from 13.7 highway to 17.8 mpg last fill-up.

I carry extra weight, lifted, 33x12:50 tires, winch & bumper you get the picture. At fuel prices alone it was worth it plus all the other positives that went with it.

 

When you install taller tires you need to get a new speedo gear to correct the speedo. The trans is using the speedo info to control the shifting.

Use your gps or cell phone to see the difference in your speedo readings and get the correct speedo gear to make the speedo read accurately.

This will make a difference in your shifting and the 'hunting' for a gear and your mileage calculations.

 

Not all years use the speedometer sensor, such as any of the cable-driven ones. The AW4 does have an output speed sensor which sits upstream of the transfer case.

Like everyone's said your transmission computer has no concept if the tire size change, all it knows is that you keep flooring the pedal. If you want this to work properly get some gears. Axles with 4.10:1 in em already can be found in XJs with the 2.5L gasser.

It's also a good idea to make sure your TPS tests good, install a transmission cooler, new Dex/Merc ATF, and this: https://www.cherokeeforum.com/f2/free-quick-fix-41821/

In the mean time keep it out of Drive when towing. Only using 3rd will reduce the amount of shifting it does.

 

I found this to be very helpful. This may be my problem also

 

XJs with 2.5 and a manual trans? Or 2.5 with the auto? I've seen a few 2.5/manual at the JY, if I passed up 4:10s I'm a be pissed.

 

2.5 liter manual and automatic have 4.10 gears.

 

Whaaaat? This changes everything. For whatever reason I was under the impression it was only the auto. ****. I've passed on at least 2 sets.

I want 4:10 on the DD.

 

Some of the autos actually have 4.56:1 lol. I don't recall which year they stopped that though.