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  #1  
Old October 28th, 2003, 06:58
OILBURNER OILBURNER is offline
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Simple Rear Driveshaft Question

Can anyone tell me why R.E. (and others) choose to use a double-cardan type driveshaft instead of a standard one?
The t-case output & the pinion are aligned just like in thousands of other vehicles which come with a 'normal' driveshaft. In fact, I can't think of a single 4x4 that came with a d/c rear driveshaft - although many came with one in the front.

Are they just selling you the more expensive driveshaft as insurance against vibrations? Has anyone had a conventional shaft built & used it with a SYE?


Thanks -
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  #2  
Old October 28th, 2003, 07:10
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BillR BillR is offline
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A standard driveshaft is used when the t-case output and the axle pinion are parallel. You use a DC shaft when the pinion is pointed up toward the t-case when using an SYE. It has to do with the u-joints being "in-phase" and their working limits.
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Old October 28th, 2003, 07:24
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jjvande jjvande is offline
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CV driveshafts allow for greater driveshaft angles because for the same angle, there is effectively two joints to share the duty.

did that make sense? im tired
-j
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Old October 28th, 2003, 07:55
OILBURNER OILBURNER is offline
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Yes I agree with both of your replies.
But for a non-radical-off-road-use, mostly-on-pavement grocery getter I am not convinced that a normal d.s. wouldn't work just fine.


Let me just stick with this question:


Has anyone replaced their slip-yoke stye rear driveshaft with a conventional one (Not the d/c style) with, say, less than 6" of lift?
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  #5  
Old October 28th, 2003, 12:53
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jjvande jjvande is offline
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yes, I had about 4.5 in the rear and I made a homemade SYE ...basically copied hack'n'tap. I ran my stock shaft lengthened and with a slip spline added. It worked fine for a few years, then i replaced the rear springs(rustys4.5") and had to get the extended shackles to make them work,.,then i got about 6" in the rear, and the angles were too much. I went through u-joints every few months. For an everyday driver, the normal shaft worked fine. I was conserned about the strength, so i decided to go with the AA TW SYE and CV shaft.

Being a college student...i didnt have time to do the u-joints during the semester, so vibes got bad until i could get home for summer and winter breaks.

I say try it if you dont want to go higher than 4.5" or so.

Anything more...go with a CV, you wont be sorry.

BTW, the cost of converting my stock driveshaft was almost as much as a TW heavy duty driveshaft.

-J
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  #6  
Old October 28th, 2003, 13:04
OILBURNER OILBURNER is offline
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Quote:
Originally posted by jjvande

BTW, the cost of converting my stock driveshaft was almost as much as a TW heavy duty driveshaft.

-J
I am going to take some measurements to see if the driveshaft angles are near (or beyond) 15 degrees at each end. If they are less, I am going to go with the single-cardan d.s. (that is, if the cost doesn't creep up near the CV cost)

I repeatedly see folks with 4+ inches of lift still running the Stock rear driveshaft. Sure some are in denial about vibes, some may not have any. But the SYE is definitely a worthy investment, plus it will decrease those angles so I am thinking it will work fine for me.
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Old October 28th, 2003, 13:10
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Quote:
Originally posted by OILBURNER
Has anyone replaced their slip-yoke stye rear driveshaft with a conventional one (Not the d/c style) with, say, less than 6" of lift?
I've had that set-up for a while after I bought the XJ. RE SYE, regular driveshaft, with t-case output shaft and pinion parallel. I have ~6" lift and it slightly vibrated when going over 50mph.
it's not that much more expensive to go with CV shaft, so just do it right the first time.
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Old October 28th, 2003, 13:28
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jjvande jjvande is offline
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think any angles over 12 degrees at each joint are too much. I was running it @12 and it was eating up joints.

Goood luck.

just go for the CV, you'll be happy in the LR.
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Old October 28th, 2003, 13:48
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The downside to the double cardan is that you then have to shim the rear axle to align the pinion with the driveshaft, in order to get a zero operating angle on the pinion u-joint. With a double cardan, you now have three u-joints on the shaft. The two in the DC unit are always in phase with each other, but if the u-joint angle at the pinion isn't set to zero then that one is always out of phase.

Personally, I would not do the double cardan unless and until I had to due to excessive angles at the transfer case.
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  #10  
Old October 28th, 2003, 13:56
OILBURNER OILBURNER is offline
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Quote:
Originally posted by Eagle
The downside to the double cardan is that you then have to shim the rear axle

Personally, I would not do the double cardan unless and until I had to due to excessive angles at the transfer case.

If you shim the rear, do you not screw up the lower shock mount positions?

I have read that 15 degrees is the magic number (not to exceed) with conventional driveshafts, but if this is so, why would jjvande have been chewing his ujoints up at 12*?
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  #11  
Old October 28th, 2003, 14:10
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TOZOVR TOZOVR is offline
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Alse think of the angles at full droop (which occurs often during even low kew wheeling) the CV allows much more angle before binding.

Re does sell the standard shafts..


Save you about $50.
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  #12  
Old October 28th, 2003, 18:43
STRYKER STRYKER is offline
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Re: Simple Rear Driveshaft Question

Quote:
Originally posted by OILBURNER
Can anyone tell me why R.E. (and others) choose to use a double-cardan type driveshaft instead of a standard one?
The t-case output & the pinion are aligned just like in thousands of other vehicles which come with a 'normal' driveshaft. In fact, I can't think of a single 4x4 that came with a d/c rear driveshaft - although many came with one in the front.

Are they just selling you the more expensive driveshaft as insurance against vibrations? Has anyone had a conventional shaft built & used it with a SYE?


Thanks -
Quickly, without reading other responses...(sorry if it's been covered already) a single cardan shaft is good to around 15 degrees. After that it starts to eat universals on a frequent basis. Further yet, and it really gets ugly.

So, the double cardan comes into play pretty quickly after several inches of lift.

70 series Broncos and Blazers all came with double cardans on the rear shafts as factory equipment. Later cost cuts by the manufacturers stopped their install on newer rigs. Which is a shame... now the purchase is up to you...despite the fact that you just paid them large amounts for the truck in the first place.
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  #13  
Old October 28th, 2003, 20:15
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jjvande jjvande is offline
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My joints were going out avery 4-6 months. ..This may have been compounded by the fact that the slip splines installed on my factory shaft when it was lengthened were going out as well.

15, 12* im not sure what the ideal "Limit" is on the angles, but mine were going out @ 12*. I got tired of taking the shaft off and pressing in new ones...i often ended up having to drive long distances with vibes in the rear. I didnt like this.

The CV eliminated all these concerns for me.
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  #14  
Old October 28th, 2003, 20:45
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Yucca-Man Yucca-Man is offline
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Quote:
Originally posted by OILBURNER
If you shim the rear, do you not screw up the lower shock mount positions?

I have read that 15 degrees is the magic number (not to exceed) with conventional driveshafts, but if this is so, why would jjvande have been chewing his ujoints up at 12*?
That 12* measurement is a static figure; when the suspension flexes and power is applied those angles can exceed 15* - that figure is only a guideline "max operating angle" anyway. In other words, the corny "your mileage may vary" statement applies here.
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  #15  
Old October 28th, 2003, 21:00
RCP Phx RCP Phx is online now
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Absolutely!!!Driveway numbers are nice but dont mean much without including full stuff/drop-out figures.You can easily exceed the operating range of the u-joints.
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