no! Don't put heavy oil in it! The 231 weren't designed to use gear oil!

 

Bwahhahahaha


^^^^^^^^^^ this. The 231 didn't have clutch pack its chain driven. Just use AT fluid as designed. I've heard stories that it can run motor oil possibly but not heavy thick oil.

 

there's tiny holes on the sides of the hollow mainshaft. The oil pump draws the ATF and pushes the ATF through it and carry it all the way to the end to the bearings where it lubricate them. The oil pick up screen is dense that it couldn't barely pull the heavier gear oil through in enough volume where sufficient lubricant would be acceptable or satisfactory.

 

Ill post pics tonight

 

i have been using gear oil in the 231 for years. I ran it in my TJ for about 4 years and never had any problems on the trail or off, driving daily. it did not give me any problems shifting either even in the winter. it was designed to use trans fluid for ease of shifting and less drag on the system for better MPG's. The pump only moves oil around the case by sucking it up and scattering it over the inside of the case. The shafts do not have holes in them for lubrication. if there were there would have to be a pump on the front output shaft or it would be starved of oil and be burning bearings.

Now back to helping the OP with his problem. change the fluid in the case and the rear and take it for a spin. You should check out the front wile you are at it too.

 

5-30 oil is fine for the 231 but let's all remember trust the OP hasn't said what TC he even has. And just for reference for the future

https://www.novak-adapt.com/knowledge/np231.htm

Some reading material

 

^^ that's true.




I can't do PDF's but supposedly there is one in this thread about the positive use of 5w30 synthetic in the place of atf.


https://www.cherokeeforum.com/f2/usi...r-case-201095/

 

have u ever taken apart a 231 before? I took apart about 40 cases and rebuilt 30 of them. Believe me when I tell you that the main shaft is hollow with holes drilled on the sides... The pump pushes the fluid from the rear all the way to front to the bearing cup. The holes on the sides spray fluid all around the mode hubs and all the moving parts. The chain itself also create splash lubrication. The gear oil is much thicker thus slower to move through the parts.

OP. please don't listen to this guy. Don't run gear oil in it.

 

I didn't know that was a pdf but 5-30 is thin enough and provides a quieter ride and wear protection according to that article. That's motor oil. Gear oil is a different beast and yes, shouldn't be used. What XJWonders is saying is true about the setup. And yes he does rebuild them. Pretty damn good BTW

 

Here's the PDF I was meaning. I've got plenty of ATF so I'll stick with it:


"It was published by Rockland Standard Gear in 2003 on how the NP231 has a habit of evaporating ATF. This is why so many wind up running dry and eventually failing. Pages 5 & 6 of this PDF: http://www.rsgear.com/articles/2003_10.pdf "

 

Ah ok, cause my link ended .htm, that's why I was curious. I've never had issues with ATF, usually use valvoline. If I ever have to drain it,I may run synthetic 5-30 too see how it feels

 

I have a 4.0 automatic with the 231. Never taken one appart before so all info is helpfull. I think the rear diff is low on oil. I noticed that with the new pinion angle and stock diff cover with dumb gromet plug that the oil level at that opening is now below even the axle tubes. So i would have to move the fill level hole to raise level so pinion can get enough oil. It was fine before a two hr road trip and shortly after. However a week later the nois started. Like all stock setups tje gromet leaks. Must have been filled higher but now its low enough to the stock level plug that the pinion cant get enough oil? Im running 33s by the way.

 

I've also got plenty of T6 5w40. What you think?

 

I made note of someone mentioning the correct level is 1/2" below the opening. You lower than that?

 

After driving 55mph the following is normal operating temp.
Transfer case = 150 F
Transmission = 150 - 180 F
Rear pumpkin = 135 F
All of this is too hot to hold your hand on. The front driveshaft will also be too hot to touch.
Metal conducts and transfers heat, TC is connected to transmission, transmission connected to engine, all metal.