baby jeep NP231 question

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Tripwire
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baby jeep NP231 question

Post by Tripwire »

baby jeep question txfr case NP 231
this year there is something occasionally "popping" under my rig coming from around the tranny/transfer case at the firewall, the sound in my brain is like the sound i imagine being the case chain slipping? it is a single pop, and is worse going up hill than on the flats

I suppose it could be the front drive shaft........

We have a ton of snow here ( for seattle) 10-12 inches and i am running cable chains on all 4 wheels

I recently had the motor and trans mounts replaced and noticed a slight difficulty getting into 2nd gear as the shifter hits the floorpan, so i'm thinking some geometry has changed?

it never does this in 2wd, so i guess the point of this is does the case use the chain in all modes or only in 4 high/low?

thanks !
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Tripwire. 86 Grand. Howell fuel Injected 360. MSD Ignition + Dizzy. 727/228 BJ's 2" Lift and 31's

88 Wrangler Howell TBI and MSD - Borla Headers w/ Cat-back + winch and 31's AND a M416 trailer

Washington State
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Cecil14
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Re: baby jeep NP231 question

Post by Cecil14 »

The chain should not be driven in 2wd, only in 4wd. It could be a loose chain, but if you've got shifters hitting body at times, I would check that before I pulled the case apart.

You can check for a loose chain by checking play at the front yoke. It won't be a definitive tell, but if it's super loose, there's a problem.


aa
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Tripwire
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Re: baby jeep NP231 question

Post by Tripwire »

thanks, forgot to add that this is a 88 wrangler original drivetrain
FSJ.ORG JOIN DATE JULY 2000

Tripwire. 86 Grand. Howell fuel Injected 360. MSD Ignition + Dizzy. 727/228 BJ's 2" Lift and 31's

88 Wrangler Howell TBI and MSD - Borla Headers w/ Cat-back + winch and 31's AND a M416 trailer

Washington State
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Cecil14
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Re: baby jeep NP231 question

Post by Cecil14 »

Really shouldn't make any difference, all of the standard part time NP cases function essentially the same. The only real difference is the size of the parts, until you get into electric shift and fancier stuff.


aa
1983 J-10 - 4.6L(MPFI)/CS130D/Hydroboost/NV3550/D300/44/44/3.54/Disc-Disc/32s/42 gallon 'burb tank
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derf
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Re: baby jeep NP231 question

Post by derf »

The chain will move in 2HI. The front tires will push it. But it will free spin in relation to the main drive shaft.

The clunk in 4WD does sound like the chain is loose. Best bet is to get it checked out.
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Cecil14
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Re: baby jeep NP231 question

Post by Cecil14 »

The YJs (at least the early ones) had a vacuum disconnect front axle. The chain will probably still move some, but it shouldn't be driven (assuming the disconnect motor is functioning).


aa
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Tripwire
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Re: baby jeep NP231 question

Post by Tripwire »

i have a modified cable front axle disconnect, it seems to be engaging correctly
FSJ.ORG JOIN DATE JULY 2000

Tripwire. 86 Grand. Howell fuel Injected 360. MSD Ignition + Dizzy. 727/228 BJ's 2" Lift and 31's

88 Wrangler Howell TBI and MSD - Borla Headers w/ Cat-back + winch and 31's AND a M416 trailer

Washington State
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Cecil14
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Re: baby jeep NP231 question

Post by Cecil14 »

If the front axle is indeed disconnecting, the only thing moving the chain in 2wd should be basic parasitic drag. You're never going to get 100% efficiency, the diff will still transmit some power (albeit very little, hopefully) up through the driveshaft.


aa
1983 J-10 - 4.6L(MPFI)/CS130D/Hydroboost/NV3550/D300/44/44/3.54/Disc-Disc/32s/42 gallon 'burb tank

rocklaurence
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Re: baby jeep NP231 question

Post by rocklaurence »

Check your front drive shaft Ujoints--make sure that its not engaged. Twist and turn it by hand while you look at the joints. Ive heard all kinds of popping, grinding , even squeeling noises from bad joints.
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Re: baby jeep NP231 question

Post by Stuka »

Since the sound only happens in 4wd (per Ops post), its most likely the chain. You should be able to feel chain slack via the fill plug in back. Make sure you can turn the front shaft by hand before hand to get rid of any load on the chain. The chain in the 208 in my J10 is kind of bad, I can feel the slack.

You can also kind of tell play just by turning the front shaft. How much of a rotation lock-to-lock.
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Re: baby jeep NP231 question

Post by Tripwire »

Thanks for your replies, i have been saving up to have the trans and case rebuilt, i am not going to do any upgrades - just gonna stay stock if i can get someone to do it for me
FSJ.ORG JOIN DATE JULY 2000

Tripwire. 86 Grand. Howell fuel Injected 360. MSD Ignition + Dizzy. 727/228 BJ's 2" Lift and 31's

88 Wrangler Howell TBI and MSD - Borla Headers w/ Cat-back + winch and 31's AND a M416 trailer

Washington State
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Cecil14
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Re: baby jeep NP231 question

Post by Cecil14 »

The NP231 is pretty easy to rebuild, kits were about ~$250, chain another ~$150, last time I looked.


aa
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candymancan
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Re: baby jeep NP231 question

Post by candymancan »

My 249 in my 5.9 pop loud if i go from drive to reverse and not give it a second to grsb slack before i take off.

I can feel it under my drivers seat... sucks... i plan to just get a low mileage transfercase from the jy and swap my newer viscous coupler i put it in it 6 years ago
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
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