What is a SYE/CV driveshaft and why do I want one?

derekmac

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I stumbled upon this on JF, and figured it might be a good bit of info for here too.

So what is a CV driveshaft and why do you want/need one?
I'm going to break this up into two different categories since there is a lot of confusion around this - non-Rubicon and Rubicon TJ/LJ's. But right now, I'll tell you neither the Rubicon nor the standard TJ/LJ have CV shafts from the factory.

What is a CV?
CV stands for constant velocity. It's a category of drive shafts that allows the transfer of torque from one direction to another.

Typical CV-joints work like this:
Simple_CV_Joint_animated.gif


These are very common on front wheel drive vehicles, in independent front suspension vehicles, and in a few other applications. They are typically stronger than comparably sized U-joint systems, but are also typically more difficult to service or replace than a U-joint due to IFS, FWD or other hardware. Materials and design does make a huge difference though.

What is a U-joint?
U-joint stands for Universal Joint. Its another way to transfer torque from one angle to another.

They work like this:
Universal_joint.gif


The U-joint is what is used in the front axles, pinions and driveshafts of all TJs.

The Cardan Shaft
This is what we all consider a drive shaft. This ultimately transfers power from your engine to your axles. They have U-joints on each end to allow for misalignment between the drive side and the driven side.

The Slip Shaft
Suspensions move up and down with terrain, and with axle flex there is even lateral movement. This means the distance between the yoke on the axle and the output of the transfer case are always changing. To accommodate this, engineers have developed a splined shaft inside the drive housing. This means the driveshaft actually changes length as the suspension moves. Its long when the axles droop low, and its short when the suspension is fully compressed. At ride height its somewhere in between.

Non Rubicon Models
All non Rubicon model TJ/LJ's have a NP231/NV231J transfer case with a Slip Yoke. This means the Slip Shaft is actually inside the transfer case. The driveshaft changes length during suspension travel by moving this shaft in and out of the transfer case.

How it works on a Jeep:
post962312.jpg


Rubicon Models
Rubicon models have the NV241J transfer case, with a fixed flange output. You can't really consider it a fixed yoke since the NV241J does not have a yoke mounted to its output shaft, there is a flange and harmonic balancer there - so I'll call it a fixed flange. The indication of fixed means the Slip Shaft is in the driveshaft. The flange on the back of the NV241J bolts to a Flange Style CV Socket Yoke, which is also part of the driveshaft.

Fixed Flange:
DSC01512.jpg


Fixed Yoke:
18676_60.jpg


Lifting your Jeep
When you install a suspension lift and/or a high clearance transfer case skid plate, you are changing the relationship between the axles and the output of the transfer case.

Because U-joints can only allow a certain degree of angle difference between the drive side and the driven side they can bind. By changing the relation between the axles and the output shaft you increase (or decrease) this angle.

On a short wheel base TJ, this is extremely important since the drive shaft is so short. Vibrations from the driveshaft indicate you are destroying the bearings inside the transfer case and the U-joints. On a LJ (long wheelbase TJ), you still need to pay attention, the driveshaft is much longer, but you are still susceptible to the same issues as a SWB TJ. Rubicon or not!

NV231J equipped Jeep's will typically install a Slip Yoke Eliminator or transfer case drop. The SYE removes the Slip Yoke from the transfer case and replaces it with a fixed yoke, like the picture above. In conjunction with the SYE, the SINGLE cardan shaft is removed and replaced with a Double Cardan Shaft.

NV241J equipped Jeep's don't have a slip yoke, they are a fixed flange output, as shown above, so they don't require a SYE. The rear of every Rubicon has a SINGLE cardan shaft. This means you can get driveline vibrations where the U-joints bind, just like a NV231J equipped Jeep. This means you'll need a Double Cardan Shaft.

FYI: Rubicon's use 1330 u-joints, whereas standard TJ's use 1310 u-joints. To swap a NV231J for a NV241J (or vice versa), you'll need new driveshafts front and rear OR just a new rear driveshaft with 1310 u-joints, and a new front yoke on the transfer case. Spicer also sells a 1310/1330 conversion u-joint which may be used. Talk to Tom Woods for your specific application questions (linked below).

The Double Cardan Shaft
Finally, this is point we've been leading up to. A Double Cardan Shaft has TWO U-joints on the transfer case side - in an area called the Head Assembly. This allows significantly more angle variation between the drive side and the driven side. This means a Jeep with altered driveshaft geometry due to a lift or high clearance skid plate can install one of these and not have to worry about vibrations damaging drivetrain components. Also notice all TJ's have front Double Cardan driveshafts, but have Single Cardan Driveshafts in the rear from the factory.

CVshaftparts.jpg


The Rear Double Cardan Shaft can be installed on a NV231J with a SYE, or it can be installed on a stock NV241J. The Double Cardan Shaft will always have the Slip Shaft built into its long axis.

Because the Double Cardan Shaft moves along the length of its shaft section it requires the ability to change the pinion angle. This means adjustable control arms or control arm cam bolts. The axle pinion must point toward the output shaft of the transfer case. Otherwise the U-joints on the axle side will wear out very quickly.

anglebetween.jpg


But I thought this thread was about CV Shafts?

Well, I can't say it any better than this:


I know I'm guilty of calling it a CV shaft, even though I know better, mostly because its such common convention...but technically it should be DC shaft, or double cardan shaft.

Maybe its miss-wording, laziness, miss-communication, who knows! But as you can see, a CV shaft is NOT the same as a DC shaft...yet they are often used to define the same thing.

A Fixed Yoke style Double Cardan shaft
Double_Cardan_driveshaft_wbolts.jpg


A Fixed Flange style Double Cardan Shaft
tomwoods.JPG


A Slip Yoke Eliminator (Fixed Yoke) and Double Cardan shaft for a NV231J
131_0905_05_z+jeep_tj_suspension_kit+slip_yoke_eliminator_kit.jpg


JK Single Cardan flange mount, Slip Shaft in center, and a Double Cardan Joint
84109-md.jpg


Flange Type Multiple Cardan Shaft - for very severe driveline angles and competition.
AA2S-F1-F1_700x120.jpg



When a Rear Double Cardan Shaft is Typically Required

As many people say - Every Jeep is different!!!

Some SWB TJ's get vibes around 2" of lift, some vibe at 1.5", some make it until 3.5" of lift. Generally, the vibes start around 2-2.5" of lift and get worse with height increases. You can augment the driveline angle I've talked about above by installing a Motor Mount Lift (MML) or a Transfer Case Drop - both point the transfer case output more toward the rear axle pinion. They also worsen the angle on the front axle pinion - but remember, it is already a Double Carden Shaft, so it will mostly likely be fine (depending on severity of the angle). Similar to LWB TJ's all the same rules apply. LWB TJ's typically experience vibes starting above 4" of lift. Even Rubicon's will experience vibrations as lift increases - they still have a Single Cardan Shaft, but they can get away with slightly more lift without requiring a Double Cardan Shaft because the transfer case output is shorter - meaning the rear driveshaft is longer, and the driveshaft angle is less severe.

Example:
- A ~2" lifted SWB NV231J equipped TJ will most likely experience some vibrations. A small transfer case drop will fix this.
- A 2.5" lifted LJ (LWB TJ) with a NV231J will NOT experience vibrations. No SYE or transfer case drop will be necessary - the driveshaft is long enough the driveline angle is not as severe.
- A 2.5" lifted SWB or LWB NV241J equipped TJ/LJ will most likely NOT require a Double Cardan Shaft. The shorter transfer case allows for a longer driveshaft - less severe angles.
- A 4" lifted NV231J SWB TJ WILL require a SYE or large transfer case drop.
- A 4" lifted NV231J LJ will likely NOT require a SYE. Slight vibes may start at 4-4.5" - pay close attention!! 4-4.5" of lift is about the max you can get out the LJ's single cardan driveshaft without experiencing some vibes. You can most likely do a small transfer case drop (stack washers) to eliminate the vibes, or install a Double Cardan Shaft (SYE for NV231J and Flange style for NV241J)

Rear Driveshaft Angle induced vibrations show themselves when you are driving. Its not as simple as whether you have vibes or not. Severe driveshaft angles will result in constant vibrations, you can feel them through the seat and they do not effect steering or handling. They will change as you accelerate and decelerate, get on the throttle or off the throttle - they are obvious. Slight vibrations will manifest similarly, but sometimes less obviously. You may have to accelerate full throttle or 3/4 throttle to feel them. While severe vibes are clearly very bad, even slight vibrations will shorten the lifespan of your U-joints & t-case.

Rule of thumb:

Total Lift Seen by T-case = Suspension lift + Skid Plate Lift

Skid plate Lift = distance output shaft moves up from stock location (usually same as advertised clearance increase)
Body Lift doesn't count - it only makes clearance for moving the drivetrain up with a Tummy Tuck.

FYI: 97-02 TJ stock skid plates hang down 4" lower than the frame, 03-06 TJ/LJ stock skid plates hand down 4.65" lower than the frame.

These are only guidelines I've experienced or observed...remember - Every Jeep is different!!! The best way is to check your pinion angle and output shaft angle (see post 2)

Vibes are not the only reason to get a new DC driveshaft!
You can pull the rear driveshaft completely off the t-case output shaft under the right circumstances of flex. It is more common on YJ's and XJ's due to the way the rear axle moves, but theres nothing stopping it from happening on a TJ/LJ either. It would seem more likely with an LJ since the driveshaft is longer, giving a false sense of no-vibe security, but even a SWB could be capable of this. Just because a t-case drop and MML will eliminate vibrations, they don't prevent this from happening.

Example 1:
CIMG5150.jpg


Example 2:
jeep035.jpg



What about pinion angle, MML's and transfer case drops?
Thats covered in post 7 below
If you are experiencing driveline vibrations, its a result of u-joints binding. The faster a u-joint turns the less severe an angle it can tolerate - this is why you usually feel driveline vibes worst at highway speeds.

Watch this video, specifically at 6:37. This is what your driveshaft is trying to do when you feel vibes.


Obviously the shaft can't flop around like that since its constrained by the pinion. But all that stress has to go someplace...that turns into vibes that wreck bearings, u-joints and other components.


—————————-

Write-Ups and Specifics on SYE Installation, driveshaft removal, driveline angles, etc:
What is a Slip Yoke Eliminator and Why Do You Need It?
Advance Adapters Slip Yoke Eliminator AA SYE Jeep TJ Installation
TJ SYE Installation
AA Slip Yoke Eliminator for the Jeep NP231 Transfer Case
Jeep NP231 Transfer Case Slip Yoke Eliminator Install | 4Wheel & Off road Magazine Article at Automotive.com
YouTube - Jeep Wrangler TJ SYE Installation

——————————-
Sources:

Constant-velocity joint - Wikipedia, the free encyclopedia
Universal joint - Wikipedia, the free encyclopedia
Drive shaft - Wikipedia, the free encyclopedia
Pirate4x4.Com - Extreme Four Wheel Drive
Pirate4x4.Com - Extreme Four Wheel Drive
Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist
Jeepwire.Com Presents: Setting Your Pinion Angle
Driveline Basics with Steve Johnson - ORN
 
More on Pinion Angle Alignment

So what about a transfer case drop or motor mount lift? Will that fix my driveline vibrations?
The answer is maybe...

The function of a transfer case drop is to make the output shaft of the transfer case parallel to the input shaft of the pinion - after a lift has been installed and the pinion sits further away from the frame. The pinion centerline and the output shaft centerline must be parallel for single cardan shafts with a slip yoke. A MML (motor mount lift) also functions to align the output shaft with the pinion centerline.

2joint_angle.gif


So why did I say maybe the t-case drop would fix vibes? - because when you lift a Jeep, the t-case drop or MML will only go so far to correct the pinion angles. The taller the lift and more flex you have, the closer you get to pulling the driveshaft completely off the t-case under flex. The best thing to do is a Double Cardan Driveshaft.

For single cardan shafts (stock shaft) - you want the u-joints to function at less than 3 degrees.
stdgd.gif

04.gif

If you can't keep less than 3 degrees at ride height then you need a Double Cardan Driveshaft.

For double cardan shafts you want the pinion u-joint centerline to be between 0.5 degrees of zero of the output shaft centerline of t-case at ride height - adjustable upper control arms allow you to rotate the pinion.

cvgd.gif

05.gif


You'll need to do the math for your application:
cv_small.jpg

Read this: Pirate4x4.Com - Extreme Four Wheel Drive

More:
Driveline 101
Driveline Basics with Steve Johnson - ORN
Jeepwire.Com Presents: Setting Your Pinion Angle
 
My transfer case has some leaking going on. I have a stock 2006 TJ Sport. I will be lifting it with metalcloak 3.5" next year and going with 33" tires. Can I install a SYE and drive shaft now and not have to replace the new drive shaft to do the lift later on?
 
My transfer case has some leaking going on. I have a stock 2006 TJ Sport. I will be lifting it with metalcloak 3.5" next year and going with 33" tires. Can I install a SYE and drive shaft now and not have to replace the new drive shaft to do the lift later on?

I'd hold off on the SYE and driveshaft until you have the lift installed. I say that because when ordering a custom double cardan / CV style driveshaft, you have to take measurements. In other words, the driveshaft you would install before the lift would most likely (I can pretty much guarantee it) not fit once you add the 3.5" lift.
 
I'd hold off on the SYE and driveshaft until you have the lift installed. I say that because when ordering a custom double cardan / CV style driveshaft, you have to take measurements. In other words, the driveshaft you would install before the lift would most likely (I can pretty much guarantee it) not fit once you add the 3.5" lift.

Thanks Chris. That's what I thought, but figured I would ask. I was just trying to save myself from having to take it out and apart twice.
 
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OK, so now that I've messed up and ordered a Zone 4", I will need an SYE and DC shaft. Can I buy a used shaft for 4" lifts and buy an SYE kit? I've found a used shaft.

The best way to order the correct shaft is to install the lift, then take the measurements needed (it shows you where to measure here).

I say that because every vehicle is different. You could buy a used driveshaft that came off a TJ with a 4" lift, but there's a lot of variables at play, and you don't know if that shaft will actually end up fitting your TJ. It may, but it also may end up where the slip joint is not where it should be when the vehicle is sitting on the ground.

So really, the only way to do this accurately would be to install your 4" lift, take the measurements, then send them to whoever makes your driveshaft for you (I suggest Tom Wood), and then you'll have to wait a few days to get it in the mail.

This is the best way to do it without chancing it.
 
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Unfortunately I don't have the luxury of waiting. I am in Cincinnati because my 6 year old son had a bone marrow transplant here on Sept 2, with my 3 year old daughter as his donor. I am from Toronto, Canada and I'm heading back for a few reasons in a week or so, which is when I'll get everything installed. Then I'm back here until after New Years.
 
Unfortunately I don't have the luxury of waiting. I am in Cincinnati because my 6 year old son had a bone marrow transplant here on Sept 2, with my 3 year old daughter as his donor. I am from Toronto, Canada and I'm heading back for a few reasons in a week or so, which is when I'll get everything installed. Then I'm back here until after New Years.

Wow... all of my prayers and best wishes to you and your family! I know what it's like to be in a situation like that where your kids are in the hospital.
 
Unfortunately I don't have the luxury of waiting. I am in Cincinnati because my 6 year old son had a bone marrow transplant here on Sept 2, with my 3 year old daughter as his donor. I am from Toronto, Canada and I'm heading back for a few reasons in a week or so, which is when I'll get everything installed. Then I'm back here until after New Years.

Wow man, that is rough. Good wishes to your little ones.
 
Thanks Chris. Hope all is well with yours.

Yes, fortunately she pulled through and she's past that hurdle now. However, I remember having to stay 10 days with her in the hospital when she was 6 months old. How heartbreaking it was!
 
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Sorry for resurrecting an old thread, but I knew I joined this forum for a good reason! I bought this 99 TJ last November as it is now, except for some engine fixes and cosmetic issues. Lift to the best of my knowledge is 4.5 in the front and 3.5 in the rear, transfer case also has a drop installed. After reading this very informative post, i took a picture of my rear drive shaft setup,,, looks as though the pinion angle is correct, driveshaft doesn't look as though it has too much angle (to me)? What concerns me is it looks as though the length is too short, thats without removing the rubber boot to actually see? Also I do get vibrations at higher RPM's.
85057

For the experts @derekmac @Jerry Bransford Do you think I should still take this apart and have a look at how much the splines are actually engaged? Or just get rid of this stock setup and go with a SYE kit plus DC drive shaft? I am looking at the length of my rubber boot compared to one pictured below from Derekmac's post.
85058
 
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Once you get to your lift height it's time to install a SYE kit into the tcase (not a difficult job) and a CV driveshaft. At your lift height the OE driveshaft is too short. Once the SYE and CV driveshaft is installed you'll be able to remove the tcase drop. You'll need adjustable length rear control arms so the rear axle's pinion angle can be raised to meet the requirement of the CV driveshaft.

This is how the rear pinion angle needs to be raised for a CV driveshaft. The pinion shaft/angle needs to be raised so the pinion points directly at the CV joint, exactly in line with the driveshaft.

CV Driveshaft Angles.gif
 
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