NP231 Black Fluid.....

clydefrog

NAXJA Member
NAXJA Member
So after 23k on the slip yoke eliminator kit I checked my t-case fluid and its black. Or very dark....I checked it about 3k after the slip yoke install and it was still red. I am running Swepco 714 trans fluid, 1987 NP231. Just wondering if this was normal with new bearings etc. I changed it of course. The Jeep sees extreme conditions only (towing, expo and 4wd) that's all i really use it for, no DD. Obviously has the V8 pumping its torque through it but thought it to be a bit odd to cause that much wear after so few miles. 23k is not much in my book to cause the fluid to go dark. Thoughts?
 

Anak

Stranger
NAXJA Member
Have you confirmed that your vent breather is properly connected and no dust is getting in there?

I only suggest that because my fluid was also black and I found that the PO had split the rubber vent tubing and it came off at some point and I didn't know it. I connected those two conditions in my own mind, though I suppose it is possible the fluid went black for some other reason.
 

trippled

NAXJA Member
NAXJA Member
If it's gets run that hard id say it's pretty normal. That stuff really needs changed often since it's such a small quantity that does so much work. Even running amsoil in mine it still gets dark pretty fast.
 

Tim_MN

Freakish Hand Strength
NAXJA Member
My thought is you need to follow a severe usage preventative maintenance schedule and replace the t-case fluid more often.
 
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srb531

New member
i recently bought a used 241 tc w/ 85 k miles on it , the fluid was black , probably never changed since new.at first use i ran cheap fluid for 200 miles then changed it to quality fluid which i change it every 6 months now . it stays red that way.
 

ehall

NAXJA Member
NAXJA Member
Its not normal. Given that there isn't any friction material in a 231, the other likely sources are contamination or temperature. I would check the breather line and vent as suggested. If that's not problematic I would probably try to figure out a way to measure temperature, especially relative to the transmission. Its a big chunk of aluminum draws a lot of heat from the trans. If its localized heat, might have a defective oil pump or a bad bearing inside.
 

clydefrog

NAXJA Member
NAXJA Member
Its not normal. Given that there isn't any friction material in a 231, the other likely sources are contamination or temperature. I would check the breather line and vent as suggested. If that's not problematic I would probably try to figure out a way to measure temperature, especially relative to the transmission. Its a big chunk of aluminum draws a lot of heat from the trans. If its localized heat, might have a defective oil pump or a bad bearing inside.
It's been awhile since I updated this.

Pump was attached when I checked (mirrror through the speedo hole).

Fast forward, I am now in Moab about 700 miles to get here while towing. The t case started making slight noise on the way here, sounds like a worn bearing. I'm gonna drain it and put some 30wt motor oil in it to get home and pull the case when I get home to see what is up. Oh also, it IS getting hot. VERY hot! My guess is slightly north of 200f. Trans lives at 150 while towing and gets up to 180 on grades so the heat isn't coming from the trans.

Definitely a bad bearing based on the symptoms. Heat, noise and fluid contaminating quickly. I will post an update after I split the case.
 

freerider15

New member
Given that there isn't any friction material in a 231
There is...technically.

If one of his bearings is going out, it could be creating a nice heat point.

I had a bearing starting to wear in my 231 years ago (when it was a full body rig).

The t-case would get hot, and when I pulled the bearing out, it was near dark blue from heat.

So, there *is* friction in the 231, but nothing normally gets that hot. Roller bearings or conical that are starting to seize will do that.

I changed my fluid rather often so mine never got that dark.
 

clydefrog

NAXJA Member
NAXJA Member
Time for an atlas? haha.
Yeah seriously considering it.

Update: went to oriellys in Moab and got some Valvoline transfer case fluid, full synthetic. Smelled like gear oil. Anyways, put it in and just ran steel bender trail here in Moab and checked the heat afterward and the t-case was not hot! Gonna see how it holds up going home/towing an 1,800 lb trailer across the salt flats at 80mph. Pretty impressed, I didn't think fluid type could make that much of a difference.
 

burntkat

NAXJA Member #1145
There is...technically.

If one of his bearings is going out, it could be creating a nice heat point.

I had a bearing starting to wear in my 231 years ago (when it was a full body rig).

The t-case would get hot, and when I pulled the bearing out, it was near dark blue from heat.

So, there *is* friction in the 231, but nothing normally gets that hot. Roller bearings or conical that are starting to seize will do that.

I changed my fluid rather often so mine never got that dark.
He's not saying there isn't any friction in the 231. (There is friction EVERYWHERE.)

He's saying there is no *friction material* in a 231. As in, the clutches/frictions in an automatic transmission. And, it's been a while since I've been in one, but I'm pretty sure he's right.

The point he's making is that, if there was friction material and it was wearing at an undue rate, it would darken the fluid (with the suspension of the bits of friction material). Same thing that happens in an auto tranny.
 

clydefrog

NAXJA Member
NAXJA Member
She blew!

I was on my way home and the transfer case went into neutral. Loud 'bang' then it was stuck in Lo range. This all happened 737 miles from home in Provo UT. Pulled the fill plug and this time there was metallic/black fluid (which I just changed roughly 300 miles ago in Moab). Luckily my father in law (who I was following) towed his TJ to Moab for wheeling, so we loaded my XJ up on the car trailer and used the TJ to tow my camper home to CA.

Gonna split the case open this week. My guess: something was dragging on the low range fork, 80 mph speed with a trailer it finally gave out. The 231 is the only stock component other than the D30. maybe it was a bit much, maybe I didn't rebuild it right 23k ago.

I will post updates with pics of the carnage once I get it apart. Just glad to be home, fun trip but Utah kinda sucked. Good scenery but backward laws that didn't make sense. Kinda glad to live in Cali.
 

TRCM

NAXJA Member
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I will post updates with pics of the carnage once I get it apart. Just glad to be home, fun trip but Utah kinda sucked. Good scenery but backward laws that didn't make sense. Kinda glad to live in Cali.

HA you live in cali and call anywhere else's laws backwards ????


:roflmao:


At least when it went, it didn't take the drivetrain with it. I had a chain let go in a NP203 doing about 45 mph, and it bound up against the front output, cracking the case, and leaving me with only rwd while out in the woods hunting.
 

Black1990jeep

New member
HA you live in cali and call anywhere else's laws backwards ????


:roflmao:


At least when it went, it didn't take the drivetrain with it. I had a chain let go in a NP203 doing about 45 mph, and it bound up against the front output, cracking the case, and leaving me with only rwd while out in the woods hunting.
California has some of the highest taxes, thats the law. I love my jeep, hence I pay thru the nose for california gasoline that the jeep needs. I hate that. Same for high sales tax on jeep parts, I hate that too, less money for jeep parts makes me sad.:tears: At least the poorly maintained highways in California are ok by my jeep, but my regular cars hate the pot holes and uneven pavement. But hey, the bullet train I am taxed for should be great for my next wheeling trip down in southern california, I just need them to introduce check luggage for jeeps, that will save me that long drive down interstate 5 which is full of potholes.


anyway the black fluid is often a sign of wear particles getting in the oil. corrosion can often cause this, ie water in the system. I had black fluid in my diff. rather than drain and refill, I drained and rebuilt. corroded gears, pitted bearing were found.

Good Luck
 

clydefrog

NAXJA Member
NAXJA Member
Def an 231. Can't wait to pop her open and see the carnage and what failed.

So Moab 1, Jeep XJ 0. I bent my uni body so bad that the right rear quarter window doesn't seal, my tail light is busted and she didn't even make it home on her own power.....so yeah.

But, it was SOOOOO worth it. Moab is sick! Can't wait to go back. Gonna bring my own beer though that 3.2% bullshit is lame.
 

burntkat

NAXJA Member #1145
Def an 231. Can't wait to pop her open and see the carnage and what failed.

So Moab 1, Jeep XJ 0. I bent my uni body so bad that the right rear quarter window doesn't seal, my tail light is busted and she didn't even make it home on her own power.....so yeah.

But, it was SOOOOO worth it. Moab is sick! Can't wait to go back. Gonna bring my own beer though that 3.2% bullshit is lame.
Man, sorry to hear about the carnage- it's a pretty truck. Wish I could see the pics!
 

kastein

NAXJA Member
NAXJA Member
In for details on what happened. Only times I've damaged NP231s it was either low oil, seized front driveshaft centering ball, or misaligned parts.
 
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