When is it necessary to install a SYE?

[Babygools99]

I've done a little bit of research here and there on an SYE kit, and there might be a thread on this already, but i was wondering at what point does an SYE kit become completely necessary to keep the driveline in order?

I believe my jeep is sitting on a 3" lift, shocks and springs, (though i dont know 100%), no BL, 33's and stock rear control arms on a ford 8.8 rear axle. I replaced the axle and left the stock arms. Am i doing my driveline a disservice by not having an SYE kit?

 

[Crashtown]

Ideally, your rear pinion should be aimed at the output shaft. If you have a lot of vibrations, have a bad pinion angle to where your bearings are leaking, or want reliability, then you should get an SYE. Some lifts come with a transfer case drop kit that drops the rear of the drivetrain down 1" with spacers between the frame & skid. Another budget remedy is rear UCA cam bolts that rotate the rear pinion angle up towards to output shaft. These may not be dead on adjustments, but every little bit helps. It is possible for the OEM slip yoke to be pulled out of the transfer case causing fluid loss on the trail.

 

[Chris]

I'd say it's necessary to do it even with a 2" lift.

It all depends though. Do you off-road? If you do, you'll quickly come to realize one of the biggest restrictions is your low hanging transfer case skid.

Do you really want to skip on a SYE and make it even lower than it already is?

If you only drive it on the street, then you're fine with a transfer case drop. But if you want to do any sort of real off-roading, you are doing yourself a huge disservice.

 

[Babygools99]

I'd say it's necessary to do it even with a 2" lift.

It all depends though. Do you off-road? If you do, you'll quickly come to realize one of the biggest restrictions is your low hanging transfer case skid.

Do you really want to skip on a SYE and make it even lower than it already is?

If you only drive it on the street, then you're fine with a transfer case drop. But if you want to do any sort of real off-roading, you are doing yourself a huge disservice.

My biggest hobby is bass fishing by far, and i bought the Jeep to build it out as an overland vehicle to do many weekend/week long trips fishing my bucket list of great bass lakes. I also daily drive it. So it's a friendly mix of long on road stretches, but, from point A to point B i would like to do as much off-roading and overlanding on the scenic routes as i can. Southeast Texas doesnt offer much but the beach and mud, and the national park situation in Texas is terrible, so i have absolutely no experience with trails that one would find in the west. These are the types of trails i would like to be prepared for as much as i can.

 

[Goatman]

First off, do NOT point your rear pinion at the transfer output unless you already have a SYE! It should be parallel to the output. Any time you are getting vibes from the rear shaft, regardless of lift height (TJs are all a bit different, so it depends on YOUR TJ) is when you should think about a SYE. If a skid drop will work and you are ok with the drop then you can skip the SYE. If you want max ground height then the SYE (and needs a new driveshaft) is the best cure. Or perhaps an engine motor mount lift could work. It is a somewhat involved decision. But oncy you have it installed you will be happy you did it.

 

[Feralkid]

It wouldnt be a bad idea to do a sye even with stock suspension.

At 3 inches you need a sye and adjustable rear upper control arms to set the pinion angle.

 

[pagrey]

A SYE is installed to get rid of vibes and really nothing else. It does very little to improve your Jeep or prepare you for anything. If yours drives smooth on the freeway now and you don't have vibes you can and should happily cross SYE off of your shopping list. When you lift or tuck and you get vibes then you need to look at your options, of which an SYE is just one of them.

 

[Babygools99]

First off, do NOT point your rear pinion at the transfer output unless you already have a SYE! It should be parallel to the output. Any time you are getting vibes from the rear shaft, regardless of lift height (TJs are all a bit different, so it depends on YOUR TJ) is when you should think about a SYE. If a skid drop will work and you are ok with the drop then you can skip the SYE. If you want max ground height then the SYE (and needs a new driveshaft) is the best cure. Or perhaps an engine motor mount lift could work. It is a somewhat involved decision. But oncy you have it installed you will be happy you did it.

I have a tcase drop on the jeep now, and its been the cause of a few "damn, im stuck" moments already, and partly the reason my dana 35 went out(that and using the skinny pedal to move some earth with that shovel of a skid plate) PO already had the jeep lifted but i measured the springs, and i believe im running a 15 1/2" front spring, which would equal out to 3.5" of lift. I got an artec 8.8 kit and welded the control arm brackets for factory fixed arms, which is what i have on the TJ now, although i do have adjustables on the way since the bushings are shot on the old ones. I don't have much, if any, driveline vibrations.

 

[TurboTJ]

First off, do NOT point your rear pinion at the transfer output unless you already have a SYE!

......and a double-Cardan driveshaft.

 

[Goatman]

......and a double-Cardan driveshaft.

Yes. The double cardan shaft is necessary with a SYE if you intend to rotate the axle. Thank you.

 

[TurboTJ]

Yes. The double cardan shaft is necessary with a SYE if you intend to rotate the axle. Thank you.

After posting that comment about also needing a DC drive shaft, I came to the realization that probably everyone that installs an SYE also installs a DC driveshaft. If you have to get a new drive shaft anyhow when installing the SYE it would be foolish to not make it a DC. Then again, using a DC means that adjustable control arms are needed so I guess it is a slippery slope.

 

[Goatman]

A SYE requires a D/C driveshaft. I guess you could get a custom shaft that has 1 Ujoint per end, but that would likely cost at least the same money. And the vibration problems come for free.

 

[Blackjack]

I am surprised with the 8.8 that you do not have one. 8.8 induces a side offset to the driveshaft that is hard to compensate for without a double cardan shaft. There is a way to do a double cardan without an SYE but I would not use if for TJs lifted more than three inches.

 

[Goatman]

The 8.8 also has a long pinion making the driveshaft shorter too. I personally don't get the allure of putting the 8.8 into a TJ.

 

[JMT]

You need an SYE and DC with 3” lift. Your TCase drop is telling you that. You may be surprised how smooth it is once you’ve done it. I thought I had no to minimal vibes. I was wrong. I had gotten used to them.

It’s expensive.
SYE/DC
Rear UCA’s (minimally, both upper and lowers would be better)
Angled rear trackbar relocation bracket
Adjustable rear trackbar

 

[Bill M.]

The 8.8 limits your options. The 8.8 offset pinion and a double cardan with a SYE will never be able to be correctly aligned to u-joint manufacture specs.

Your transfer drop has caused your front drive shaft to now be misaligned also.

 

[Blackjack]

The 8.8 also has a long pinion making the driveshaft shorter too. I personally don't get the allure of putting the 8.8 into a TJ.

The 8.8 was a solution when there was a shortage of Dana 44s out there and a lack of products to help the Dana 35. There were plenty in the junk yards and could be had for cheap but those days have passed.

 

[B34C0N]

I'll be the one to suggest it because I've been running it for 2 years.

If budget is extremely tight or you don't have the space currently to do a shaft replacement SYE there is a hack n tap method available. When I went from 3 inch lift with tcase drop to 4inch still with the tcase drop I started getting vibes. Really really bad. I didn't have a garage or the fund to pay a shop to put an SYE in, so the hack n tap went in to hold me over.

I'm finally working on kit based SYE to get rid of the tcase drop and hack n tap.

If you ever hit your drive shaft on a rock though, it would be bad news.

 

[GEEP4ME]

It’s expensive.
SYE/DC
Rear UCA’s (minimally, both upper and lowers would be better)
Angled rear trackbar relocation bracket OR Adjustable rear trackbar

This. The 3" suspension lift I put on made it undriveable. I don't mean, kinda shaky, sort of buzzy. It felt like it had square back tires, LOL. With 1.5"-1.75" of homemade transfer case drop, it was "driveable", but would shake a bit taking off from a stop. Taller motormounts might have been just enough to solve the issue, but....go big or go home?

A budget lift, does not get the job completed. I knew that I might need an sye (and therefore a double cardan shaft) AND adjustable control arms.....and the adjustable track bar. I was hoping that I'd get lucky. Now that I've had it all done and how bad it was before it was ALL done, I can't see how any one particular Jeep could squeak by without.

Had a guy pass me on the highway last summer. TJ, doors off, mudded up, hard top, boot hanging outside, at least 33s if not 35s. I wondered what his suspension setup was. Thought there was no way he did what I did and be able to run that speed down the road. And how many others were running around with just some coil springs and washers between the transfer case drop and frame, LOL.

 

[iviscus]

A SYE is installed to get rid of vibes and really nothing else. It does very little to improve your Jeep or prepare you for anything. If yours drives smooth on the freeway now and you don't have vibes you can and should happily cross SYE off of your shopping list. When you lift or tuck and you get vibes then you need to look at your options, of which an SYE is just one of them.

I just bought 4 inch RC. And new rear driveshaft no sye. I don’t do heavy off road just sand and mud during vacation. Should i buy the sye???