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Unread 06-01-2012, 05:07 AM   #1
cmorse444
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Do I need an SYE and CV?

There are many threads discussing them but none say if you need both. I'm doing a 4" RC lift and may end up getting a SYE if needed. If I do get an SYE must I get a CV with it?

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Unread 06-01-2012, 05:13 AM   #2
Anticanman
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If you get a SYE then you need a cv driveshaft to compliment it. Unfortunately with RC, you may have vibes when you install the lift but a year later it'll fix itself. Stick with a transfer case drop.

Read more about driveshaft angles from the master:
http://www.4xshaft.com/driveline101.html
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Unread 06-01-2012, 07:03 AM   #3
janders82
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i did the 4" RC lift on my 94 YJ. Its only my trail rig and not my DD. I don't get any vibes. The springs were a little stiff at first, but i trashed my trac bars and the ride is great compared to the shot stock springs that were on my rig before. You're going to get LOTS of opinions, but I haven't had any issues with the lift on or off road...yet

you def need an CV Driveshaft if you're going to do the SYE. I went with the TC drop that comes with the RC kit for a while which seemed to work out great, but the drive angles are pretty steep. I'll save you my story, but i ran into issues a few months after installing, which I blame on the angle of the DS. Every rig seems to have its slight differences, so you may be able to get away with a TC drop for a while. if you can afford the SYE i'd go for it. Chances are that you will be going that route in the future regardless.
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Unread 06-01-2012, 01:02 PM   #4
PA_YJ19
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If u don't want to deal with the cv and sye right now then order a set of 1 inch lifted motor mounts and shim the rear axle correctly. This will take away ur severe angle by point the yoke on the transfercase downward a few degrees and sum 6 or 8 degree shims would prob do the trick to line up the yoke on ur rear axle correctly. Just figur I'd give ya another idea if u don't feel comfortable getting rid of ur current setup. This would allows u to beef up ur motor mounts, which r weak in my opinion and give u a better angle for ur stock shaft.
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Unread 06-01-2012, 06:47 PM   #5
fratis
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No you dont need a cv shaft with an sye...you simply wont be able to take full advatage of the sye conversion. You will still need a driveshaft that has a splined slip incorporated as the sye eliminates the slip in the tcase obviously. The only people who dont use a cv shaft with an sye are those who have already sourced a cheap or free standaed yoke shaft that has a slip in it. If you are planning to buy both then you wont save any with a noncv shaft. Yes it is technically possible.
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Unread 06-01-2012, 06:52 PM   #6
fratis
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Quote:
Originally Posted by janders82 View Post

you def need an CV Driveshaft if you're going to do the SYE. I went with the TC drop that comes with the RC kit for a while which seemed to work out great, but the drive angles are pretty steep. I'll save you my story, but i ran into issues a few months after installing, which I blame on the angle of the DS. Every rig seems to have its slight differences, so you may be able to get away with a TC drop for a while. if you can afford the SYE i'd go for it. Chances are that you will be going that route in the future regardless.
So in reality it didnt work "great." Vibrations are only one problem resulting from an improperly set up driveline..
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Unread 06-01-2012, 07:53 PM   #7
4x4JB
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This was in the sticky frequently asked questions. Pretty good info. Not sure if it helps but it'll give you more info on your decision.

SYE and CV Driveshaft
The topic of SOA and SYE and CV Driveshaft comes up way too much. The SYE (Slip Yoke Eliminator) is used to remove the slip yoke that come stock on all YJ Wranglers. The kit is typically used when a Jeep reaches a point where the driveshaft angles become too steep to operate without vibration. While the amount you can lift a Jeep without a SYE varies it is typically necessary at 2.5-3”. Some guys can run a 3.5” SUA lift without vibration others get vibs at 1.5”. The 2.5-3” area is a ball park. The amount of lift achieved with an SOA lift with stock springs is between 5 and 6 inches. Many times people use a transfer case drop to lower the transfer case about an inch to achieve better driveline angle and reduce vibration. A big problem with this is that even with the drop and the minimum amount of lift (~5”) the driveline angles are going to be similar to a Jeep with a 4” lift without a transfer case drop. So even with the drop the angle is still pretty severe.
There is another advantage to the SYE. If you decide to not use a traction bar and use a slip yoke with a transfer case drop then do not be surprised if the slip yoke slides all the way out of the transfer case. The pinion can rotate up enough to pull the driveshaft out of the transfer case. Because the transfer case design the way it is ATF will then spill out everywhere because the case is sealed around the yoke.
Trying to cut corners in this area is difficult. Some look to a “Hack and Tap” type SYE kit. This involves cutting the existing transfer case output shaft and using a flange adaptor to turn the output shaft into a fixed mounting location. This cost around the same amount as a full SYE because you need the adaptor which will seal the transfer case near the output shaft. This job is done by the slip yoke in a stock set-up. A TJ transfer case is sealed before the driveshaft and is cheaper than a set-up for a YJ. Another benefit of the full SYE set-up is the increased spline count in the in new transfer case output shaft.
The CV driveshaft is necessary to deal with the larger angles of the lift. Even if your driveshaft was long enough to use with the SYE there is no slip in the shaft. The shaft slides in and out to allow for changes in the distance between the pinion and the output shaft of the transfer case. This was accomplished in the old set-up through the slip yoke. Any change in distance the yoke would slide on the output shaft. Without slip when the Jeep flexes parts will break because there is no way to account for the change in distance.
There are a couple of ways to go about this. The first is to order a driveshaft from a vendor. Most likely they will want the distance between the yokes of the pinion and the transfer case. It comes in the mail and you bolt it on. The other option is to have a front 4WD XJ shaft cut down to the correct distance.

http://www.4x4wire.com/jeep/tech/shaft/diydriveshaft/

Standard SYE vs Hack and Tap
http://www.tomwoodscustomdrivelines.com/index.html

http://www.tomwoodscustomdrivelines....DYOKEKITv2.pdf
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Unread 06-01-2012, 09:51 PM   #8
jeepyj13
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I had my rc lift for over a yr. It was good with no vibs just with a tcase drop. As soon as I added a 1" lift shackle shortly after that though I immediately got vibs and shortly after that replaced the shot ujoints. I definitely need a sye kit and cv shaft because I still have vibs.
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Unread 06-02-2012, 11:34 AM   #9
janders82
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Quote:
Originally Posted by fratis View Post
So in reality it didnt work "great." Vibrations are only one problem resulting from an improperly set up driveline..
thanks for the comment. first off, i'm fairly new to the game. i said it "seemed" to work out great. in reality it was only masking the problem.
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