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np231 low range rev limit?

O

outlander

NAXJA Forum User
Location
Columbus,Ohio
Over the weekend a friend and I were wheelin in an open muddy field while in 4 wheel low range.We were having a blast but i started to wonder how much fun is too much fun for a np231 in 4wheel low??

I seem to remember 25mph is the speed limit for a 231 in low and 55mph in 4hi.Im asking what is the rpm limit...Ive honestly never seen a rpm limit mentioned before,just a 25mph speed limit.

I got to thinking about it while we were romping around in 3rd gear (ax15) in 4low with the tach sometimes reaching 5k rpm wouldnt that mean the internals of the 231wouldbe spinning at around 12k rpm because of the 2.72 reduction???
 
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i dont see how rpms would matter, it be spinner at a lower speed at 5k in first gear compared to 1500 in 4th, that being said ive ran a few of my 231's at high rpms/speeds without issues, just make sure they got plenty of fluid as they dislike being dry
 
the pcm should have a built in rev limiter but it will limit rpm and not speed . well some pcm's had a 90+ mph speed limiter. so in 4x4 hi or low it will engine rpm and not vechicle speed.
 
unless it's a 90 or earlier you have a rev limiter at 5250rpm iirc. That means your max tcase input RPM (in OD or 5th) will be approx 7000rpm. tcase in low range reduces the output shaft speed, doesn't increase the input shaft speed.
 
The Tera-flex has a max recommended RPM fot their 4:1 kit,IIRC its about 3500rpm.
 
RCP Phx said:
The Tera-flex has a max recommended RPM fot their 4:1 kit,IIRC its about 3500rpm.
Click to expand...
That is so you don't go deaf from the whine in their gears.:roflmao:
 
Divide, not multiply - the output spins slower than the input. 5000/2.72 = 1840RPM
 
yeah I think I said that... apparently he missed it. The absolute fastest is when it's on the rev limiter in 5th/OD.
 
Well, im sure everybody on here will call me a "noob" and will tell me I don't know what i'm talking about.. But! The 231 is one thing on all my XJ's that I have never broke/even had a problem with. You would have to know me to know how hard I run these things. 4LO launching on dry pavement all the way through the gears. Yes, rev limiter in OD which is like 65 mph in my current rig. They're either tough or i've just had really REALLY good luck with them. :wierd:

Anyways, I've never had too much "fun" with one.
 
I have only blown one up and it probably would have lasted longer if I had kept it filled with fluid or replaced the rear seal when it blew instead of after driving 2 hours home on the highway.
 
When we go duning through Glamis it's all 4LOW and you are reving the crap out of that motor to make it up some hills. The 231 just keeps on tickin!
 
I've had mine wound out in 5th gear, 3-4K RPM for an extended period of time. It's not yet broken.
 
Ok I feel a little better about thrashing my jeep last weekend afte rreading the replies.I probably shouldnt be worrying because my 231 is a 231HD from JB conversions that has all the upgrades including 6 pinion planetaries.

Guess im being paranoid after running my stuff hard but i hear a whine that goes away when i let off the gas... first thought is R&P but the sound comes from the tranny hump area.I dont have carpet or insulation so maybe im hearing normal AX15 gear noise?
 
My 231s have always made a little noise when in 4wd. If you want you can check chain tension in it, if it's too loose you should replace the chain but that's about it.
 
I take my jeep to the beach a lot. Lots of fast 4 wheel use.

I'm on 4.56 gears, and 32's, and even in 4low, I think I've gone well over 25 mph. It makes some noise, but it's still healthy and working well.

I even mashed the gears 2 weeks ago shifting into 4hi out of 4 low, and it's still working fine.
 
kastein said:
yeah I think I said that... apparently he missed it. The absolute fastest is when it's on the rev limiter in 5th/OD.
Click to expand...

And if you're in 5th/OD in 4 low, i'm betting something else is going to go first...
 
UNCC_99XJ said:
And if you're in 5th/OD in 4 low, i'm betting something else is going to go first...
Click to expand...

Not so far. You can pick up some decent speed in 4lo on deserted snowy roads :D

I have only broken shit in first/second. Unless you count ramming my front skid into something in fourth, and that just ruined my lap time :(
 
Everything healthy the worst I'd expect is heating the fluid up and maybe losing some out the vent, keep an eye on fluid levels and rock and roll.


PS - There isn't an upper limit on speed in 4-high, at least not per my 1989 manual, that says that you shift into 4-high at "any legal speed."
 
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