rear driveshaft...carrier bearing. on an MJ

87 SWB comanche. np231 with SYE, 6.5" lift with aw4 trans and 4.0 HO conversion.

bent my rear driveshaft the other day playin on the rocks with 89eliminator.

took it off so I can drive in FWD to work tomorrow since the company van has now fried all of it's electricals (bad body to motor ground strap, I think...clears everything, starter won't turn over, engine won't run when it does turn over).


anyways. here's the plan.

have the rear driveshaft retubed...but made to the length of a front aw4 driveshaft.

get the proper carrier bearing and have an intermediate shaft built. this shaft will go from the t-case, through the carrier bearing, and have the proper yoke on the back of it to allow me to bolt my double cardan rear driveshaft to it.

build a crossmember at the proper position, which sits between the frame and flush mounts. at the same time build a trans crossmember which sits between the rails too. this will allow for one very nice belly skid between the trans and that crossmember...giving me t-case protection.

it will also allow me to have both driveshafts at the same length. the rear driveshaft currently uses a thicker tube than the front, and so it will remain my dedicated rear driveshaft. it's also currently a double cardan driveshaft.


so, the goals:
uniform driveshaft length allowing me to carry one spare driveshaft.
zero parts hanging down, full belly protection.
less chance of contacting the driveshaft on rocks due to a slightly steeper DS angle.
Not having to change pinion angle since the intermediate shaft will be adjusted accordingly.


does anyone have any input on this? It's only a concept at the moment, but I really think it can work.

-Pat

Edit: sorry, didnt catch the SWB Commanche part of your post. Is there that much of a difference in shaft length?

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Its a good concecpt if you were driving an extended cab or 4 door pickup, but the front DS is darn near the same length as the rear shaft on your vehicle. You would only have about an inch or two to play with to build your intermediate shaft, which obviously wouldnt work.

I think I read it right anyway...

For example, I have a 96, with 6.5" clayton long arm, aw4, np241OR (same length as a 231). I have front and rear tom woods double cardan shafts, and they are roughly the same length. I now carry my old front double cardan (OEM) drive shaft as a spare, it will work for both the front and the rear shaft in a pinch.

Unless I am reading your post wrong, what you are describing wont work. Get under your jeep with a tape measure and you will see what i mean.

~James

yes there is at least a foot to a foot and a half of spare space on a swb MJ.

longbed a front driveshaft is half the length of the rear, if that.

I think it's possible, as long as the carrier bearing is dropped a few inches below the t-case output shaft - you don't want to put too severe of an angle on the second shaft when the suspension drops.

My '91 S-10 x-tra cab short bed 4x4 had a 2 piece shaft/carrier bearing set up and the 3" Rancho lift I had on it came with a t-case drop and a carrier bearing drop to keep the angles appropriate. Don't see why a carrier wouldn't work on an MJ.

Definitely post up pics if you fab this up.

Hmm... then it sounds like a good idea to me. My old Tacoma had a split rear shaft and it worked great. You could easily grap something from the JY to fab it all up...

Post pics for sure.

~James

i thought the MJ was about 10" longer wheelbase?

Thats a cool idea, but I am not sure it is really worth the expense (if it is overly-expensive). I have wheeled my MJ pretty hard for the past 2-3 years, and know others that do too, and we really haven't had any real issues with bending the rear drive shaft(s) on our SB's.

Like I said, it is a cool idea though, if you do it, you'll have to link up some pics.

Andy in Pa. said:

Thats a cool idea, but I am not sure it is really worth the expense (if it is overly-expensive). I have wheeled my MJ pretty hard for the past 2-3 years, and know others that do too, and we really haven't had any real issues with bending the rear drive shaft(s) on our SB's.

Like I said, it is a cool idea though, if you do it, you'll have to link up some pics.

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the reason he bent it cause he hit the rock pile a decent speed. it dented my tranny pan on the same rock pile.

If you put an intermediate shaft in it's angle is going to have to be the same as the TC output shaft to keep it vibe free, so that will detirmine the height of the support bearing.You could use a double carden for your intermediate shaft and not have to match it's angle to the TC, but that's going to add alot to the the cost.

If your increasing your rear shaft angle then your going to have to match it to you pinion angle also.

It's a cool idea, but like mentioned, cost may not be on your side.

Sero said:

If you put an intermediate shaft in it's angle is going to have to be the same as the TC output shaft to keep it vibe free, so that will detirmine the height of the support bearing.You could use a double carden for your intermediate shaft and not have to match it's angle to the TC, but that's going to add alot to the the cost.

If your increasing your rear shaft angle then your going to have to match it to you pinion angle also.

It's a cool idea, but like mentioned, cost may not be on your side.

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cost won't be too much.

end benefits will be great.

the truck already has a double cardan rear driveshaft...the cost of retubing the shaft is minimal, and the ujoints don't need replaced or serviced since they have only about 4000 meticulously greased miles on them.

the idea is to drop the intermediate shaft just enough to keep the driveshaft in alignment as it is now...matched (within 2 degrees to allow for torque and axle pinion up-travel under load) to the pinion.


the end benefits would be:

A) MORE suspension droop...much more. dropping the cardan a few more inches and moving it back a foot or so will give it about 5 more degrees of droop, even with the fact that it will be shorter. currently it can touch the ground and then some without binding.
2) less cost on rear driveshafts...I break it, I replace it with a front driveshaft since that is the length it will be set to. I have about 4 spare front driveshafts.
C) only one spare shaft on the trail needed...saving weight and space in the bed for other parts etc.

89eliminator said:

the reason he bent it cause he hit the rock pile a decent speed. it dented my tranny pan on the same rock pile.

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lol. hey, I got to the rock pile at low speed...then goosed it. that's different than hitting it at a different speed.:roll:

jeepcomj said:

the truck already has a double cardan rear driveshaft...

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yes but if you want the intermediate shaft to have a different angle than your TC output shaft it also will need a double cardens shaft, so 2 double cardens between your TC and diff.

Sero said:

yes but if you want the intermediate shaft to have a different angle than your TC output shaft it also will need a double cardens shaft, so 2 double cardens between your TC and diff.

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that's not true. it uses a Ujoint, and a Ujoint os obviously capabable of making a 2 or 3 degree angle. it's never gonna move anyways.

jeepcomj said:

that's not true. it uses a Ujoint, and a Ujoint os obviously capabable of making a 2 or 3 degree angle. it's never gonna move anyways.

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Ofcourse a u-joint is capable of making those angles, but it needs another one on the other end of the shaft with equal angle to cancel the vibration...intermediate shafts do not have a u-joint at the other end, they have support bearings....research it more you'll see

http://www.rodandcustommagazine.com/techarticles/0608rc_driveshaft_tech/photo_02.html

http://www.dennysdriveshaft.com/c10_2_piece_driveshafts.html

The only u-joint before the support bearing is at the transmission......

no shit sherlock.

the problem with your thinking is that a carrier bearing can handle any angle.

ONE ujoint at the transfercase

stub (intermediate) through carrier bearing

double cardan AFTER the carrier bearing

Ujoint at axle.


the carrier bearing doesn't have to be mounted vertical. it can take a couple of degrees of angle at no issue. it's all in how you mount it.

and if you notice, neither of those units have a double cardan at the transmission end of things. they have spicer adapter flanges, or a ujoint and slip-yoke.

This is from post # 10

jeepcomj said:

the idea is to drop the intermediate shaft just enough to keep the driveshaft in alignment as it is now...matched (within 2 degrees to allow for torque and axle pinion up-travel under load) to the pinion.

Click to expand...

As I'm trying to point out...it cannot be done with an intermediate drive shaft since it only has 1 u-joint.

jeepcomj said:

no shit sherlock

Click to expand...

But it seems you know everything and are quite mature.. so good luck with it....

jeepcomj said:

and if you notice, neither of those units have a double cardan at the transmission end of things. they have spicer adapter flanges, or a ujoint and slip-yoke.

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Yes but if you look at how these are installed, the intermediate is IN-LINE (as in ...0 degrees) with the transmission/TC output shaft, not on an angle. It cannot be done any other way unless you change that front u-joint to a double carden. As someone mentioned earlier, their lift kit included a drop bracket for the TC and shaft, so the shaft stayed in-line with the TC.

I'm just trying to help you bud....but don't let my 20+ years in the trade fool ya....I'm done.

k.

take a look at a semi truck once. the intermediate shaft on many peterbuilts I've helped my dad work on are NOT in-line with the output. and they're that way from factory.