Can my stock rear driveshaft handle this or do I need a CV driveshaft? - JeepForum.com

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post #1 of 18 Old 01-11-2017, 01:11 PM Thread Starter
Charley3
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Can my stock rear driveshaft handle this or do I need a longer driveshaft?

My 99 XJ has a 242 Tcase and C8.25 rear diff. It is lifted 1.25 inches front and 1.75" rear, Bilstein 5100 shocks for a 3-inch lift, Antirock front swaybar, no rear swaybar. extended brake lines long enough for a 3-inch lift. My front springs are long (but soft) OME TJ Light Load Front Springs. My rear springs are OME XJ Light Load rear springs. This is not a cheap budget boost lift. I think my articulation is about same as a typical 3" lift.

I've been using OEM XJ shackles, but am soon going to install OEM MJ shackles, which are 1.2 inches longer. Then I might have even more rear axle articulation.

I still have a stock rear drive-shaft and no slip yoke eliminator. This has been working fine with 1.25 inches lift and XJ shackles. It has no vibrations on highway.

However, I'm starting to worry about after I have MJ shackles and possibly more droop-flex than it does now... Could my rear drive shaft pull apart or my transfer case be damaged during articulation or droop?

Do you think my stock drives-haft can handle that amount of droop/articulation? Will I need to get a slip yoke eliminator and a longer drive-shaft?


Warning: I often edit my posts a few times to get them complete or correct errors.

Note: I had heart surgery Mar 2016. I wasn't feeling well since, but I improved this Dec 2016. Now I'm feeling better and getting back to Jeeping, modifying and wheeling.
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post #2 of 18 Old 01-11-2017, 01:22 PM
Fourtrail
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As long as you don't jump the jeep you should be fine.... The centered differential doesn't move that far vertically when the rear axle articulates. If you are worried about too much droop, you can always add a single limiting strap in the center of the axle, but I would not worry about it.

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post #3 of 18 Old 01-11-2017, 06:56 PM
S8NNG8
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What leads you to believe you have the articulation of a 3" lift at only 1.25"?

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post #4 of 18 Old 01-11-2017, 07:33 PM
UltimatE
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Shocks, brake lines, and shackles are supporting mods to increase flex without breaking these things. Springs are your limiting factor in up travel and droop. Your driveshaft is perfectly fine, since you really have the equivalent of an Upcountry suspension.

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post #5 of 18 Old 01-13-2017, 12:06 AM Thread Starter
Charley3
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Since I have a 242 Tcase and C8.25 rear end, my rear drive-shaft is shorter than XJs with a 231 Tcase or other differential.

My 1.25" front, 1.75" rear lift isn't a budget boost. It's a custom low COG lift designed to ride comfortably and corner well on-road and articulate off-road as much as a typical 3" lift. I tried to think of everything when I configured this custom lift, but I forgot about the possibility of potentially over-stretching the stock rear drive-shaft during articulation or droop. I don't think that's a concern with XJ shackles, but I'm not sure with MJ shackles. I'll explain below why this lift has way more flex than a budget boost lift.


Quote:
Originally Posted by UltimatE View Post
Shocks, brake lines, and shackles are supporting mods to increase flex without breaking these things. Springs are your limiting factor in up-travel and droop. Your driveshaft is perfectly fine, since you really have the equivalent of an Upcountry suspension.
I have much longer shocks, brake lines, and springs than any budget boost lift, no rear sway-bar, a Currie Anti-rock front sway-bar. The combination of those items theoretically allows the same flex as a 3" lift. Next I will put on MJ shackles, which in theory might increase my droop, unless my rear shocks will be the limiting factor for droop. Am I missing something here?


Quote:
Originally Posted by S8NNG8 View Post
What leads you to believe you have the articulation of a 3" lift at only 1.25"?
This is not an ordinary 1.25" lift. My front springs are soft rate, long OME TJ springs and my rear springs are flexy OME light load XJ springs. With a stock weight XJ I'd have 1.5" to 1.75" lift front and 2" to 2.25" lift rear from those springs, but I have a lot of skidplates weighing me down so for that reason my front is 1.25" and rear is 1.75". I call it a 1.25" lift, but there's more to it than it sounds.

I have a Currie Anti-rock front swaybar and no rear swaybar. So I do not have any swaybars that limit my articulation. My shocks are Bilsteins 5100 for 3" lift shocks. The shocks extend enough to allow a 3" lift to articulate. I have adjustable length front JKS LCAs. It articulates well.

This setup already articulates-flexes a lot with stock XJ shackles. I flexed it on a ramp and it pulled on my stock rear brake line during articulation, which is why I installed longer brake lines.

If I change from XJ to MJ shackles on the rear, will that increase flex and/or droop? I think that's already been answered, but anyone feel free elaborate.

The normal limiting factors for articulation are springs, shocks length, swaybars, brake lines, and possibly LCAs; but in my case those things are all modified, and soon my shackles will also by modified (changed to MJ shackles, which are approx 1.2" longer than XJ shackles).

I've experienced its articulation and it's impressive, especially for an XJ with only 1.5" lift (averaging front and rear heights). I'm building a sleeper. So ya, I think it does flex as much as a typical 3" lift. Would MJ shackles increase articulation or droop?

Well maybe not. While typing this, I realized that longer rear shackles might not increase articulation if my shocks (long enough for 3" lift) are the limiting factor for articulation. However, MJ shackles might increase my axle droop, if my shock length doesn't limit droop. So maybe droop will only be increased when it's up on a car hoist-lift? Maybe I have nothing to worry about. Am I missing something here?

Those are the reasons why I'm sure it articulates and droops more than any 1.25" budget boost. I think the articulation is around what a 3" lift does. I don't know if MJ shackles would increase droop. If so, should I be concerned about to much droop over-stretching drive-shaft or tcase output shaft when wheeling?

If it's a concern, I could get a slip yoke eliminator and a longer drive-shaft. It might not have to be a CV shaft. Just a SYE and a longer shaft with U-joints might do fine (since my ride height on highway is only 1.75" rear). But maybe I don't need to do anything with my drive-shaft?


Quote:
Originally Posted by Fourtrail View Post
As long as you don't jump the jeep you should be fine.... The centered differential doesn't move that far vertically when the rear axle articulates. If you are worried about too much droop, you can always add a single limiting strap in the center of the axle, but I would not worry about it.
I won't be jumping it, but I would like to enjoy as much articulation and droop as I can on the trail, but I don't want to over-stretch my drive-shaft or tcase output shaft.

Warning: I often edit my posts a few times to get them complete or correct errors.

Note: I had heart surgery Mar 2016. I wasn't feeling well since, but I improved this Dec 2016. Now I'm feeling better and getting back to Jeeping, modifying and wheeling.
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post #6 of 18 Old 01-13-2017, 01:00 AM Thread Starter
Charley3
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I think the simple question for me to ask is this: With a 242 Tcase, C8.25 diff, and the short stock drive-shaft, could a 3" lift (while articulating off-road) over-stretch the short stock drive-shaft (or stock 242 Tcase output shaft)? That's my concern-question.

I'm not worried about drive-shaft on-road since my rear ride height is only 1.75" and I have no vibrations.

As far as MJ shackles go, after more thought, I'm guessing they won't change articulation or droop much (if any) compared to XJ shackles because I'll still have the same length rear shocks (shock length for 3" lift). Does that sound right?

Warning: I often edit my posts a few times to get them complete or correct errors.

Note: I had heart surgery Mar 2016. I wasn't feeling well since, but I improved this Dec 2016. Now I'm feeling better and getting back to Jeeping, modifying and wheeling.
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post #7 of 18 Old 01-13-2017, 05:37 AM
RedJeepster1
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The simple answer is no, you are going to be fine. I have a 4.5" lift in one of my XJ's, (granted it is a manual transmission which is shorter than the auto, but its much higher so it should make up the difference here) and it still has a stock driveshaft that does not bind. My DD is at 1.5" of lift with full leaf packs and stock shackles and I wheel it all the time and have never had an issue. I have had it on the lift and I believe there is definitely enough room in my setup to run the longer shackles without any driveshaft bind. When letting my axle droop with the shocks unhooked (so they are not a limiting factor), everything spins freely. If you have any vibration on the highway you could always put a couple washers between the cross member and the unibody to space the cross member down only as much as you need to.

As was said previously, the only time your diff will drop that far is if you were to jump it, and even then I believe you would be fine. The best way to know would be to put it on jack stands and let everything spin though.

PS, the 242 is the same length as the 231, the real factor in driveshafts is the transmission.

88 YJ with a 4.6l stroker, AX-15, NP231, 2.5" lift, 4.10's and 33's
2000 XJ w/ 350k+, AW4, NP231, Locked Rear, HD Crown Leafs, trimmed to fit 33's
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post #8 of 18 Old 01-13-2017, 11:59 AM
UltimatE
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The NP242 is the same length as the NP231. The 8.25 pinion is only ~one inch longer than the D35. At 29.5" vs 30.5" driveshaft length, there is only half a degree difference in u-joint angle, and at such a shallow angle to begin with, there is practically no difference in the two.

-Matt

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post #9 of 18 Old 01-13-2017, 10:29 PM Thread Starter
Charley3
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I do have an automatic transmission, but you guys probably already figured that out since I have a 242 transfer case.
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post #10 of 18 Old 01-14-2017, 04:21 AM
Timo_90xj
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I don't think you will any problems even after adding the longer shackles. 1.25" longer shackle raises your rear by half of that, which is just over half on inch. Your eventual lift height in the rear will be around 2", which the stock rear DS should handle easily.

If you do get vibes after the shackle lift, it's most likely from the longer shackles causing the rear pinion to rotate out of alignment in relation to TC rear output angle. If that happens, you either need to shim the rear axle, or cut off the leaf perches, rotate axle, and re-weld perches.

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #11 of 18 Old 01-14-2017, 04:46 PM Thread Starter
Charley3
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Timo, I'm not worried about vibrations because my eventual lift height will be the same as it is now because my homemade custom rear bumper will lower the rear half an inch while the MJ shackles will raise the rear half an inch. So my net lift height will be the same after those mods (and I don't have any vibes now).

I was concerned that my droop might increase after MJ shackles and over-stretch my rear driveline when I'm off-road (my extended shocks and brake-lines are long enough for 3-inch lift).

Warning: I often edit my posts a few times to get them complete or correct errors.

Note: I had heart surgery Mar 2016. I wasn't feeling well since, but I improved this Dec 2016. Now I'm feeling better and getting back to Jeeping, modifying and wheeling.
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post #12 of 18 Old 01-15-2017, 01:50 AM
Timo_90xj
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I had a 4.0 + AW4 + 242 with a hack 'n tap SYE + Ford 8.8, using a stock front DS in the rear. OME 2" leafs, about 1" lift built into the spring pads, and boomerang 1" lift shackles.

DS slip spline travel from full bump to full droop IIRC was something of around 1" to 1.5" - in other words, you should not have any issues at full droop even with an OEM slip joint @ the TC as long as you have enough spline engagement.

Old pic of my XJ, rear not even at full droop. Those are 35s.


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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #13 of 18 Old 01-15-2017, 06:47 PM Thread Starter
Charley3
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Quote:
Originally Posted by Timo_90xj View Post
I had a 4.0 + AW4 + 242 with a hack 'n tap SYE + Ford 8.8, using a stock front DS in the rear. OME 2" leafs, about 1" lift built into the spring pads, and boomerang 1" lift shackles.

DS slip spline travel from full bump to full droop IIRC was something of around 1" to 1.5" - in other words, you should not have any issues at full droop even with an OEM slip joint @ the TC as long as you have enough spline engagement.

Old pic of my XJ, rear not even at full droop. Those are 35s.

I highlighted the part in read that made my eyebrows go up. Can I safely assume that I have enough spline engagement?

Is that you in the pic Timo? The fellow in the pic looks like a young Ragnar Lothbrook (in the TV series Vikings). You're XJ looks like my prior XJ (similar year, color and trim package).

Warning: I often edit my posts a few times to get them complete or correct errors.

Note: I had heart surgery Mar 2016. I wasn't feeling well since, but I improved this Dec 2016. Now I'm feeling better and getting back to Jeeping, modifying and wheeling.
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post #14 of 18 Old 01-16-2017, 01:20 AM
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Once you are done with the shackle install, measure the spline engagement, and check how much available in- and outravel you have on the slip yoke. If you have +/-.75" it should be plenty enough. You need an absolute minimum of 1" of spline engagement, but preferably 1.5" for smoother operation and less wear.
I can't remember exactly how much the rear axle on an XJ moves forward and back during suspension travel from full bump to full droop, but it really isn't that much.

IIRC it's less with the leaf springs as it is with the quad-link front (or rear of a ZJ/TJ). My ZJ has about 5" of uptravel and 6" of downtravel in the rear. My rear DS slip joint total in-out movement through travel extremes is about 1.25"


Yeah, that's me in the picture about 7 years ago. I look a bit older, and I've got more beard these days

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #15 of 18 Old 01-16-2017, 10:40 AM
75SV1
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I can only speak as to the Hack-n-Tap. As I remember the driveshaft had 1 inch movement to the front and 2 inches to the rear or would that be articulation. I have roughly 4.5 lift, auto, 8.25 rear end. I drove with the stock shaft for about a year. I was getting some driveline vibes. The H-n-T took care of that.
If I was Charley, I'd unbolt the driveshaft from the rear end and see if it would slide forward about 1 inch. Then see if roughly 2 inches rearward. The instructions with the H-n-T kit wanted 1.25 splines minimum on the T/C output shaft.
I don't have the experience of the others in this, but as long as you don't go all out "Dukes of Hazard' I doubt you'd have problems.
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