For some reason I am having a hell of a time trying to find the speedometer gear for the NP242 with the 215/75R15 tires. The reason for replacement is the speedo is bouncing like the teeth in the gear are broken.

Reading the online charts look to point to 35 teeth, I see something like this:
However, it shows for the 231. Do the 231 and 242 use the same gear and sensor assemblies?

 

I believe so, although don't quote me on that. It would stand to reason since it's measuring driveshaft rpm. I DO know that rotational positioning is important for different gear sizes and they are marked on the case. It's possible yours has rotated out of position enough to be skipping teeth.

For that price, you could try a junkyard gear. It doesn't have to be from an XJ either. I would think one from a ZJ would work as well. WJ's don't use a gear.

 

So best I can tell it does not matter if the TC is a 231 or 242.
Also appears they are color coded.
Assuming you have 3.55 gearing looks like a 35 tooth for 215 75 15's.
I believe the part number to be 52067635. Just like the one at your Amazon link.
But here is what I am confused about. They list all the gear ratios.
Now I recognize the 4.11 cause I think that is 4 cylinder gearing.
I recognize the 3.07 cause I believe that to have come in the manual tranny ones.
But they list 3.50 and 3.70 which I don't recognize. I do know 3.55's and 3.73's.
I thought my Jeep was had 3.55 gearing.
Anyway here are some shots out of my '00 parts catalog so you can see what I am talking about.

 

delete

 

Yeah that wasn't helping my confusion either not to mention I see the brand Michelin under a couple to.
So I figure we just ignore all that. LOL.
But I was glad that I looked at my parts catalog. I run 225 75 15's on some Ecco rims.
Hoping to use the Icons I sourced, as part of my clone build, with some 225 70 16's.
Which was the size tire that would have come from the factory.
Now I have read that the speedo gear is the same for the 2 but now in my parts catalogs I actually see that it is. MLOL.

 

Awesome! Worst case, Amazon is great about returns.

Whenever it comes to 242 info, it seems most of the topics relate to "why doesn't this WJ 242 seem right in my XJ?"

 

Not a problem.
You just have take what I said with a grain of salt.
Never replaced one so have no first hand experience with this.
If you noticed I used phrases like "best I can tell", "it appears", or "I have read".
They all mean the same thing:
"This is what I think I know." LOL.
Anyway hopefully the color coded part is correct and as you said Amazon is good with returns.

 

Absolutely, this seems to be one of the few areas of the Cherokee that isn't largely known

 

Why not pull it out to see if it's chewed up and verify the existing tooth count. It's just one bolt on the retainer clamp then pulls straight out. The whole assemble can rotate to 4-different positions to accommodate the different gear sizes, so mark it before pulling it out.

 

Okay here's the skinny on the 242 from the WJ. It fits and works, but has no speedometer gear in the output. The speedo gets it's information from a sensor inside the transmission that reads the teeth in the parking lock wheel, the rear wheel ABS sensors, and the converter turbine shaft speed. All this info is processed by the PCM and displayed on the dash. You COULD get it to work by replacing the output shaft and the tail housing, but that's a lot of work.

Unfortunately this system has no compensation for different tire sizes or gear ratios unless the PCM is programed for it. One of my friends put it well. "The XJ is an offroad vehicle capable of being driven on the street whereas the WJ is a street vehicle with off-road capabilities." That about sums it up.