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NP242 Fluid change

Old 11-03-2016, 01:22 AM
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Default NP242 Fluid change

HEY guys, have a 2003 jeep GC been doing alot to it and I just replaced new cv axles hubs bearings and I as thinking it's time for a fluid change. But I was wondering if anyone had a write up or a step by step on how to do it. I know there's YouTube but I want yalls opinion!

ALSO looking for ideas for things they have went wrong with yours maybe I could check out on mine!

Thanks Joker

GC details:
I6 220k miles
35 rear end
Selec trac (242)
30 front end.
2.5 Suspension lift with new springs and shocks.
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Old 11-03-2016, 08:04 AM
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Always pull the upper fill plug first. Some folks have had trouble removing that one and if you pull the drain plug first but can't get the fill plug out, you're screwed.
Correct fluid is ATF +4 or DEX/MERC.
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Old 11-03-2016, 09:41 AM
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I was one of the screwed guys with a stuck fill plug. I ended up welding a Allen wrench to it and finally got it out.


AFT +4 is what is called for, but I think people recommend it because of the possibility of mixing oils between the trans and TC and I think the factory did it so they would not have to carry two separate oils (simpler). but mixing oils between the trans and TC is not possible because even if the oil gets past the seal it will leak out the bottom between the trans and TC. when I had my TC apart there were no clutches (just gears and a chain) so I question why automatic trans fluid rather than gear oil. anyone have a reason?
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Old 11-03-2016, 12:11 PM
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ATF+4 is a temperature stable high pressure lubricant and all you need for ball/roller bearings and a chain. The gears are in constant mesh just like inside an automatic transmission. Low drag, high shear lubricant. The pump just circulates the fluid and doesn't build pressure anyway.
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Old 11-04-2016, 02:09 AM
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Would this be a reason I have issues sometimes getting my TC to shift per say I guess the pressure has to build up inside there right? For it to engage. ALSO do I fill it till it starts running out like a differential
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Old 11-04-2016, 02:47 AM
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You misread. The fluid just circulates to lube and carry off heat. Inside it's just like a manual transmission with a planetary section for low range. It's either engaged or not engaged. The only t/cases with clutches are the 249 and the new 247. Those have self contained viscous clutches filled with their own fluid, like a fan clutch. Actually, I think the 247 has an open clutch, that's why it needs special fluid.

Yes, you fill it until it runs out the fill plug. Also, like a diff, the low fluid level is one finger-joint below the fill plug. The manual says 1/2". Close enough!

Damn! Sometimes it's like pulling teeth! This stuff is simple if you read your manuals.

The main reason for a rounded out fill plug is it's 10mm, not 3/8"! Use the right wrench and you won't screw it up! I can't tell you how many I've found when working at Valvoline! The 10mm is a tight fit in the plug and sometimes you have to clean out the mud to get the wrench to fit. I can almost guarantee a 3/8 will screw it up.

Last edited by dave1123; 11-04-2016 at 03:09 AM.
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Old 11-04-2016, 10:05 AM
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For comparison to gear oil ATF is approximately 7w. And like Dave stated its a great pressure oil.


If anyone has a owners manual for a 96 grand laying around please let me know.
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Old 11-04-2016, 10:39 AM
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Thanks I'm looking into getting me a haynes manuel. They say those things are worth there wieght in gold.
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Old 11-04-2016, 12:09 PM
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Actually, the Haynes manual is a good source of basic information for common maintenance and repairs, but THE BEST one out there is the Full Service Manual from pacificcoastmanuals.com. You can download it for $8.95+tax. It's about 93mbs of compressed pdf files that cover every system on your specific year jeep. No searching for your exact application. It has explanations of the systems and how they work, how to diagnose problems, where to find the components, and how to get to them. It has lots of good circuit diagrams and over 140 pages just on the transmission. You can print out just what you need, get it dirty, then throw it away when you're done if you like!

This is a copy of the Factory Service Manual used by the dealer techs. There's no "refer service to qualified technicians" like Haynes tells you. Where do you think I get most of the information about WJs I post here?

BTW, the Jeep Owner's Manual is just instructions on where the buttons are and what they do, and how to change a tire!

BTW, ATF+4 supersedes all previous ATF specs because of the high shear additives in it. It's also very temperature stable in that it doesn't get thick or thin out enough to matter.

Last edited by dave1123; 11-04-2016 at 12:24 PM.
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Old 11-04-2016, 12:14 PM
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so just to get this right because I'm about to drain my t-case and both were mentionned in previous posts, is it atf+4 or dexmerc that is recommended for the t-case? or it doesn't matter?
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Old 11-04-2016, 12:20 PM
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i had a bunch of black plastic come out last fluid change

20,000 miles later still doin fine, dunno what it was
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Old 11-04-2016, 12:47 PM
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Probably the nylon "slippers" from the shift forks. I'm thinking it's a 249 and you haven't used low range much, right?

In a 242 or 231, it doesn't matter much what you use for fluid, but Jeep recommends ATF+4 because it's high shear additives reduce fluid breakdown. New Process Gear specified DEXTRON when they first made t/cases. Any changes after that were Chrysler's doing. GM used DEX III and Ford used DEX-MERC. Actually DEXTRON-MERCON was developed to use in both. All of these are designed as automatic transmission fluid as their main function.

Last edited by dave1123; 11-04-2016 at 12:59 PM.
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Old 11-04-2016, 01:09 PM
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Thanks this is amazing source of info
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Old 11-04-2016, 01:27 PM
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Originally Posted by dave1123 View Post
Probably the nylon "slippers" from the shift forks. I'm thinking it's a 249 and you haven't used low range much, right?
yeah the consensus was the shift fork pads when it happened...but not proven yet...

its 242...wife uses the 4lo all winter long to get in/out our driveway, makes her feel cool/tough.
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Old 11-04-2016, 02:11 PM
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Yeah, low range has that effect! Engine working hard and you just barely moving!
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