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Unread 09-22-2013, 10:23 PM   #1
ZJMatt
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1998 ZJ 
 
Join Date: Jul 2012
Location: Weare, New Hampshire
Posts: 484
NP249 to NP242 swap - rear driveshaft

This is probably covered somewhere in the sticky thread but I'll be honest here. I'm too damn lazy to go through 113 pages of the thread to hopefully find what I'm looking for!

I just finished the swap, only to find out my donor driveshaft is WAY too short.

Spent all day on it. All that's left is to adjust the linkage (got the adjustment bolt loose with acetone + ATF mixture, but the rods are rusted together), add fluid, put my skid plate back on, and..... find a new drive shaft.

My jeep is a 98 with the 5.2. Had an NP249 with an internal slip yoke. I bought an NP242 transfer case from a 96 4.0 with an external slip yoke. The junkyard I bought the transfer case from doesn't save drive shafts, so I was SOL there. But my local yard had 4 of them. Long story short they're stuck up pricks (never had a good experience there but they're 5 minutes down the road!) and grabbed a random one off the shelf (not allowing me to measure to pick the longest one), told me it wouldn't work and since I was buying a part that obviously wouldn't work in my jeep they didn't want it back if it didn't fit.

Well you guessed it, it was too short. Measures 28" weld-to-weld going from both the far ends of the welds.

With this shaft installed, it is only engaged onto the splines about 1-1/4".

There is another junk yard about an hour away with a 29.5" ESY shaft. I'm guessing this is the one I'm looking for? 2-3/4" still doesn't seem like a lot on a 4-3/4" slip yoke, but is much better than what I have now. I don't even dare drive my jeep on the road the way it is.

Is the 29.5" shaft the one I want, or am I best to take my original driveshaft (measures 31" W-W), separate it into two pieces at the u-Joint, and put it back together with the ESY end on it? That should give me 4-1/4" of contact between the shaft and slip yoke. Now I'm wondering, is this TOO much? Wondering if I'd have issues during rear suspension up-travel , with the shaft being jammed into the case too far.

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Unread 09-23-2013, 07:27 AM   #2
Snowfan2
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1998 ZJ 
 
Join Date: Jan 2012
Location: North of Amarillo, Tx
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You might need a shaft about 1" shorter than original. I have one that is balanced and has new greasable ujoints. 150 plus shipping. I'll measure the length and post back shortly.
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Unread 09-23-2013, 08:11 AM   #3
ZJMatt
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Location: Weare, New Hampshire
Posts: 484
Well the 29.5" shaft would be 1.5" shorter than stock.

Remember I also have a 4.5" lift
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Unread 09-23-2013, 11:36 AM   #4
ZJMatt
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So I found a place closer that had one of the 29.5" shafts. Went and picked it up... this is what it looks like installed. Not sure how I feel about this... it is engaged about 2.5" I just don't like how there are still splines showing that aren't in the slip.

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Unread 09-25-2013, 04:33 PM   #5
shaban
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1996 ZJ 
 
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Location: Yarraville, VIC, AU
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I've currently got an old-style 242 which got same slip yoke style as 249, reused the old driveshaft with no trouble at all.
Was thinking of putting in a newer 242 with an external slip yoke, that requires a shorter driveshaft.
Here's some data I've found on driveshaft swaps (some numbers could be wrong though):
jeep_rear_shaft.jpg  
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Unread 09-25-2013, 05:16 PM   #6
shaban
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I found 3 rear shafts, measured them all (ujoint to ujoint center, weld to weld center)

- Original from a 4.0 ZJ with ISY 249: 33.25 u-u, 29.5 w-w
- 4.0 ZJ with an ESY 242: 31.5 u-u, 28 w-w
- 4.0 XJ with an ESY 242: 28.75 u-u, 25.25 w-w

There's about 3.5-3.75 difference between ujoint-to-ujoint and weld-to-weld . I take u-u as more accurate, really.
shafts1.jpg  
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