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  #1  
Old January 6th, 2018, 22:40
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clydefrog clydefrog is offline
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NP231 Black Fluid.....

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?
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Old January 7th, 2018, 07:00
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Anak Anak is offline
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Re: NP231 Black Fluid.....

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.
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Old January 7th, 2018, 07:50
trippled trippled is offline
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Re: NP231 Black Fluid.....

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.
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Old January 7th, 2018, 07:50
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Tim_MN Tim_MN is offline
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Re: NP231 Black Fluid.....

My thought is you need to follow a severe usage preventative maintenance schedule and replace the t-case fluid more often. It's not like the job is difficult or time consuming.
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Old January 7th, 2018, 07:57
srb531 srb531 is offline
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Re: NP231 Black Fluid.....

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.
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Old January 7th, 2018, 19:12
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ehall ehall is offline
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Re: NP231 Black Fluid.....

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.
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Old January 7th, 2018, 20:35
burntkat burntkat is offline
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Re: NP231 Black Fluid.....

It could be related to the chemistry of the fluid used, too.
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