Okay, I bought this Jeep...

... 89 2 door, 4 liter, AW4, NP231, Dana 30/35. When I got it in November, it was already lifted 5.5-6" running 34" buckshots and a locker, but overall pretty mild, fairly low budget, and very effective.

Thing is, it still runs a slip-yoke, and honestly, it runs fine (or did). The rear diff is rotated up, so the pinion is about in a straight line with the driveshaft, and all the angle is in the top u-joint.

Everything I've read anywhere says this thing should shake itself to pieces before you get outta the driveway, but it drives great. I got a little vibe accelerating past 25 or so, then its smooth above that.

I drove it for months like this without a problem, until the lower u-joint crapped out on me. Replaced the joint, put it back on the road.

Took it wheelin, and on the way home, the lower u-joint (the brand new one) let go. This time the flopping driveshaft ripped the tailshaft housing off the t-case and bent the snot outta the output shaft.

So I'm at a crossroads...

I can put it back like it was fairly cheap. I know I oughta do the SYE while I've got it apart, but I'm having a really hard time blowing $600 on a very low-budget rig, to fix what I don't see is a problem. All my grief has come from that bottom u-joint, not the top one with all the angle in it. The SYE won't do anything to change that bottom joint, and it won't eliminate vibrations I don't have.

So, why did this thing work at all to begin with? And do I really need the SYE? If so, why? And, is "low-budget Jeep" simply a contradiction, and I gotta just suck it up?

Thanks

Robert

The problem with running the slip yoke at anything above factory height(and even sometimes at factory height) is that it puts MUCHO added stress on the output bearing for the main shaft. Dillinger is very adamant about this because he had a T-case seize on him because of this. I would say, go ahead and get the SYE. By the time you get all the new "stock" parts you'd prolly be at like 450 anyway. You might try and track down someone w/ a non-bent mainshaft to send in as a core for Tom Woods(that would save you a chunk of change). But yeah, this is one of those, "suck it up and fix it" type deals. HTH, Peace

Ary

P.S. Got any pics of this beast?

also by installing a SYE, you'll be running a longer drive shaft due to the shortened length of t case output shaft, this in it's self will really help your angles .

the problem with not doing it right, is that you'll just keep breaking the same part, which will in time really get you into trouble. Trust me, been there.

keep in mind that if your XJ is low budget, then when you're ready to sell or build another, your parts will have more value than the whole truck, including your new SYE.

you could drop the t case and add a longer slip yoke from rustysoffroad.......I personaly would go for the sye.......

You have a few options short of a full SYE.

First, maybe there's a reason the rig was sold -- maybe it was eating u-joints and the guy who lifted it didn't know why or how to fix it, so he passed the problem on to you.

Bottom line is, the u-joint angles must be the same (within a degree or less) or the u-joints operate "out of phase" and things break. So what are the options?

(1) Replace the tail cone, go with a stock or YJ slip yoke, and re-shim the axle to get the angles correct. Not a good choice -- at 5"+ of lift, even the YJ slip yoke will have only marginal engagement on the t-case output shaft.

(2) Replace the tail cone and get a new driveshaft made up, but if the pinion angle is at zero, have the driveshaft modified to include a double cardan joint at the transfer case end (the front driveshaft already has a double cardan if you don't know what I'm talking about).

(3) Replace the tail cone. Get the low-budget "hack-n-tap" SYE kit, and have your drive shaft modified with a slip spline in it. At this point you have two sub-options: (a) run a conventional u-joint on each end of the drive shaft and reshim the diff so the angles are the same at each end of the shaft, or (b) have the shft made up with a double cardan at the transfer case end and leave the pinion angle at zero.

Thanks guys...

For the record, and to give props, the guy that built it does know what he's doing, he's also encouraging me to just do the sye. But I'm cheap.

And I understand all the theory behind the sye, and why my setup should not have worked. I was just tryin to figger why it was working, and why I should fiddle with it since it was.

I still don't think it broke 'cause of the slip yoke. I don't really know for sure, but like I said, it was that lower joint, the one with no angle in it. And as I understand it, after a $300 sye, and a $300 new d/c driveshaft, that rear u-joint will be exactly like it is now...

But thanks again, I do appreciate the voices of experience, even if I am too hardheaded to agree right away! :dunce:

Robert

With a zero degree angle and a sye, the rear u-joint won't be any stronger than it is currently. Did the second u-joint seize up from lack of grease and break or did it just snap? Might have been an install problem.

I meant lower u-joint, not rear u-joint.

"Did the second u-joint seize up from lack of grease and break or did it just snap? Might have been an install problem."

Yeah, I realize it mighta been me, but what I really suspect is that I got crap (water mud whatever) into in while wheelin, and burned up the bearings.

My point is, that I really don't think I'm having "angle" problems, so a sye seems unneccesary.

But everybody (with more experiance than me!) seems to think otherwise!

Thanks,

Robert

I'd go for like Eagle said (that guy is an XJ god.). If you truely can't afford an SYE I'd re-shim the axle to get both those U's at the same angle, although you'll probably have to go for a YJ slip joke if you do that as you'll be pulling the slip out a bit.

I don't think that the lower u-joint problem would be fixed by a sye. That would just fix a vibration problem that he says doesn't exist. The joint will have no angle whether there is a sye or standard with his setup. Theoretically, the upper u-joint should be the weakest link because it is running at an angle. Also, only buy Spicer joints. Some of those foreign joints aren't worthy of being a paper weight.

Ok,lets get this straight. The axle end is *about in line* with the driveshaft? My question would be is the axle rotated *too far* upwards? When under load,the axle's pinion will rotate upward,and if the angle is already *about in line* with the driveshaft,it seems to me that it could be easily rotating past the "in line" point and putting and amazing amount of stress on the joint. Better check that out *first and foremost*

"it could be easily rotating past the 'in line' point and putting and amazing amount of stress on the joint"

See, that makes sense to me. It is "inline" when static. So yeah, it would bend back when accelerating. I kinda figgered 5 degrees was 5 degrees, up or down shoulda been the same stress, but I guess that's not right.

So I at least need a longer driveshaft, so's I can bring the pinion back down where it oughta be. That brings me, cost-wise, close enough to the whole shebang that I can stomache it.

But won't this same thing happen with the sye? Isn't the goal there to get the double-joint at the top/front of the shaft, and a relatively "straight" joint" at the rear/bottom? Or do I rotate the pinion back down even with the sye?

Thanks again, you guys are great...

Robert

You are Georgia Mike are still ignoring the fact that unless the angles at both ends of the shaft are the same (within about one degree) the u-joints on the respective ends are not operating in phase with one another. That alone puts stress on both u-joints, irrespective of which one is at the greater angle.

It's difficult to explain exactly what being in phase means. It has to do with the fact that the four nodes of a u-joint don't always travel at the same rotational velocity as they go through one revolution. That's why a constant velocity joint is called a "constant velocity" joint -- because it is designed so that the components DO always operate at pretty much a constant rotational velocity.

If you have a u-joint at one end of a shaft that has a zero angle, it will always operate at a constant velocity. A joint at the opposite end that's at an extreme anle won't. That sets up internal binding between the two joints and whichever is the weaker will fail first.

A double cardan joint puts two u-joints in a single housing with a ball between them to ensure that they always operate at the same angle and are thus in phase. The u-joint at the other end of a double cardan drive shaft is set to a zero angle because the two joints in the DC unit are in phase and self-cancelling, so the third joint has to be at zero so it doesn't introduce an out-of-phase condition into the assembly.

Not meaning any disrespect,Eagle,but I do know what "in phase" means,as well as understand that in a perfect world both angles would be the same under load,but we don't live in a perfect world,and I would be willing to bet that more often than not,they aren't the same. This is in NO WAY saying that I think it's right,those are just the facts.

My point was simply that if his pinion is rotating upwards past the centerline of the driveshaft,the u-joint WILL fail. If we all had the $$$ for a SYE we wouldn't be having this discussion,but some of us can't afford it (or are too cheap--like me) My advise was that if he wanted to "fix" it,he should inspect the pinion's current position,and rotate it down a little if necessary. This would at least get him back on the road until he could afford to dish out the money to fix it the right way.

Again,I'm not trying to start an argument,I'm just trying to clear things up a little.

Couple of things you need to check on your rig: First of all, is the drive shaft the right length? Is it properly balanced? Were ALL the U joints replaced after the Jeep was lifted? How are the angles of the T case output and the pinion to each other? With a single cardan they must be nearly parallel with about a 1 or 2 degree down angle on the pinion. Is the u joint binding, especially when the axle is at full droop? Was the U joint installed correctly and of the correct type? If the U joint was installed 180* out of it's balanced position it'll give you nothing but trouble. Is the cross member & tranny mount in good condition? Engine mounts? Are any suspension bolts loose? Check these things out as they will affect U joint life- with or without the SYE.

Most folks who have driveline vibes after a lift are those running the Chrysler 8.2 or whatever. The D35 is more forgiving

Same boat

I have a 3.5 inch lift (rancho packs, 3/4 inch shackle) and the pinion and the driveshaft are almost inline. All the angle is in the Tcase side Ujoint and I have almost no vibs at all.
Its hard for me to justify speinding 600 dollars on an SYE and new driveshaft when (As it seems now) dont have ant problems.

Georgia Mike said:

Not meaning any disrespect,Eagle,but I do know what "in phase" means,as well as understand that in a perfect world both angles would be the same under load,but we don't live in a perfect world,and I would be willing to bet that more often than not,they aren't the same. This is in NO WAY saying that I think it's right,those are just the facts.

Click to expand...

I didn't say you don't understand it -- I said you're ignoring it. If you are advising the man to leave a setup with a 5-degree-plus angle at the upper u-joint and a zero angle at the pinion, =his drive shaft WILL be operating out of phase, and it WILL continue to eat u-joints.

I offered three (actually four) relatively low-budget solutions, all of which address the phasing problem. It's up to him if he wants to fix the problem, or pretend it doesn't exist (or is due to some other cause) and continue to blow u-joints.

Sorry, guys, I didn't mean to start a spat!

It's clear though, that I have to do one of two things:

[A] Fix the angles so the two are at least as close as possible, or
Do the short-shaft swap, lose the slip-yoke, and get a d/c driveshaft

[A] looks easier, but there's no way the driveshaft I've got now will reach if I swing the pinion down. So I'll need a new driveshaft either way.

And since my t/c output shaft is bent, that'll need to be replaced too, whether I go sye or not. (This is the part Eagle missed, which makes his low-budget suggestions appreciated, but less low-budget)

So if I gotta replace both shafts anyway, I might as well do it right, instead of saving a nickel now that'll cost me a quarter down the road.

By the way, Tom Wood's has a H/D sye & driveshaft combo for $525 shipped, no core required. Quadratech has a similar sye for $260, so I guess I'll see what that driveshaft will cost me locally.

Thanks again for everybody's input...

Robert

AAww shucks! No spats here. Just good ol' discussion. Eagle's points are well taken by me,he's a smart guy! I'm in the same boat as you with the output, and my pinion is the same as yours,only I'm @ 4" of lift. Almost in line with the driveshaft (about 3 degrees down IIRC) and I have a slight vibe around 20-30 MPH. After that,it's smooth as silk. Works for me,but YMMV. BTW,go with Tom Woods' stuff. It's his main business,so he knows what he's doing. No matter how much $$ you save with some other "mail order" business, it'll never replace good ol' customer service (which is something you can't put a $$ tag on when you REALLY need it)!
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