How fast in low range NP231?

[Darkwing327]

Looking for opinions on what everybody thinks.

2005 TJ 4.0 6 speed NP231. Transfer case has Tera2Low.

While hunting I drove 190kms the last three days in low range. Usually in 3rd gear going up the forestry roads and 4th coming down. RPMs are normally kept at 1800-2000. Running synthetic fluid in the TC. Do not need 4wd at any point, it is just the steepness of the inclines. If I am in HI range I am either spinning at 3000rpm in 1st or going way too fast on the rough roads in 2nd at 2000rpm. Then at every pothole and corner I would be hunting 1st-2nd in HI.

I do realize that I am increasing the wear usage on the TC in LO, but probably only 500km a year at most as opposed to the 200,000km in HI it has had in its lifetime so far.

My 'butt' tells me that driving in LO range is easier on the Jeep as a whole as I can slow down and speed up through rough sections easily, whereas when in HI the need to keep the RPM up to not lug puts the entire buggy through rough patches at too high a speed. However something has to take the abuse when in LO, which would only be the TC.

So the ultimate question is this - I am causing any issues by running in LO range for days on end at 30km (20mph) top speeds. Lots of transfer case whine in LO which sounds normal. Perfectly quiet in HI. Real world numbers would be in 8 hours of driving - 2 hours 4th gear 30km/h - 6 hours in 3rd or 4th at 15km/h. Also consider I am not under wheeling load at any time...just driving.


Thanks for your thoughts.

 

[Jerry Bransford]

I wouldn't run 4Lo at 20 mph.

 

[NashvilleTJ]

The whine you reference hearing in 4low, but not in 4hi, is because on your transfer case 4 low gearing comes from engaging the planetary gear set which is on the front of the tcase - right behind the tranny. As Jerry noted, it is not good to run on the planetary at high speed for long periods of time.

The tera low 4-1 cases (which I ran way back in the day) were often crazy loud when engaged. My screamed like a banshie - it whined so loudly it was embarrassing. (I also ran the tera2low like you do - and I always thought that was cool).

i know it’s a pain, but get used to shifting down into low only when you need it - stick with hi when you don’t.

 

[pagrey]

The planetary gears in the transfer case are what's whining like @NashvilleTJ says. If you don't mind rebuilding the case more often it's no big deal. The rebuild kit on those cases is maybe $150 and a new planetary is around $250 if you completely fry it. If those numbers don't sound high then go for it. It's not going to explode, just wear faster.

If I was going to do it I would send the oil out every time I had it changed for analysis and check the temp of the case after I ran for a few hours to see if it was getting hot and go based on that information, not opinion. NP231 cases aren't expensive or too difficult to swap, it's something I'd experiment with if I was in your shoes.

 

[Darkwing327]

The planetary gears in the transfer case are what's whining like @NashvilleTJ says. If you don't mind rebuilding the case more often it's no big deal. The rebuild kit on those cases is maybe $150 and a new planetary is around $250 if you completely fry it. If those numbers don't sound high then go for it. It's not going to explode, just wear faster.

If I was going to do it I would send the oil out every time I had it changed for analysis and check the temp of the case after I ran for a few hours to see if it was getting hot and go based on that information, not opinion. NP231 cases aren't expensive or too difficult to swap, it's something I'd experiment with if I was in your shoes.

That was kinda my thought as well...putting the wear into the transfer case (which as you say is cheap), as opposed to screaming along in 1st on an NSG370 transmission, which is about as far from cheap to rebuild on a jeep as you can get. $5k around these parts. I am not running in 4wd more than about 2 minutes a day when crossing a big water bar or something, so not stressing anything other than the planetary. As mentioned I feel better about wearing that than taking the pothole, washboard and rut hits at the higher speeds of 2nd gear - no matter how much I am watching the roads, they seem to sneak up out of nowhere and jar the jeep pretty violently at times. I am aired down to 15 psi which helps a lot as well.

I am out hunting pretty much every day for the next 6 weeks. Will take along my temp probe and shoot a reading once I am at the top of a good climb.

The one point a buddy mentioned is that his Rubicon manual states to keep speeds under 25mph (40kph) in LO. Understandably I can see that as not applying to my multi-hour trips, but a 241 runs at 4:1 whereas my 231 is 2.7:1 I believe, so my TC bits would be spinning at considerable lower speeds, no?

Thanks again for the replies.

 

[Darkwing327]

Update:

Good advice @pagrey

So went out hunting again (snagged a nice 4 point buck finally). After running up a long climb in 2LO - 3rd and 4th gear - I shot the temp of the transfer case at 108 F...transmission was at 127 F...so looking pretty good. I was fairly cool, so will recheck again next year in the heat and see what we see. For now, not worried at all...will just swap out fluid twice as often as it is cheap.

Thanks again for the sensible advice

 

[nathanotis]

I'm with Jerry (as usual). 20 seems fast... In fact, I think if you've ever thought, "Is this too fast for 4Lo?", it's probably too fast.

 

[Darkwing327]

I'm with Jerry (as usual). 20 seems fast... In fact, I think if you've ever thought, "Is this too fast for 4Lo?", it's probably too fast.

Sorry, going to have to stick to @pagrey line of thinking on this one. When something mechanical is put under stress it creates friction and heat. This clearly is not happening from what I can see. The one thing that Jerry got incorrect that you are quoting is that I am not in 4wd, but 2wd...so there is less mechanical stress on the TC. Yes, the chain is still spinning as they always do in our Jeeps, but there is no front axle load.

Not trying to be argumentative, I just have to believe the temp readings.

 

[Apparition]

I've accidentally run down the highway at 55 mph with mine in low range. I don't recommend it but nothing broke. I bumped one stick into low when shifting the other to hi, rubicrawler problems.

 

[freedom_in_4low]

What is your gear ratio? Not that it changes any of the advice given, I just find that the nsg370 has a low enough first gear with 4.88 and 35s that I have trouble thinking of a situation where i would have this issue. I had it more often with 3.73/32s and an Ax15. I spend a lot of time on dirt that I could go 60 on if smooth but the washboards, potholes, and embedded small rocks put me in that 20mph territory.