Bad Vibration after Front Driveshaft Install

[kevman65]

Okay, now calm the hell down and actually SEARCH for what you think is out there.

It isn't made for the JL/JT platform. There is no TRUE CV joint, all the CV joints you'll find are double cardan. There is no high angle zreppa.

There is no other option, short of custom ordering (you think what's out there is expensive) exactly what you want, and no one offers a warranty for a zreppa high angle for the JL/JT.

You need to get out of your perfect world laboratory and actually search for some of the things you preach.

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[ShadowsPapa]

Key points to remember:
You need two single cardan or cross type joints running the same angles in proper phase to cancel each other out - to restore even rotation to the driven shaft or device.
You should try to run no more than about 10 degrees for even shaft, and driven component RPM.
The type of driveshaft in question - the OP's shaft, has a double-cardan joint at one end and a single at the other.
The double cardan joint works on the transfer case end because it's going to self-smooth out rotational speeds, no matter the shaft angle from the transfer case.
If the front of the t-case is pointed up, doesn't matter as long as each single joint of that pair is under 10 degrees. So the shaft can be running 20 degrees from the transfer case output - pointed up in the front and down in the rear (DUH, and mechanic knows that)
The problem is that the OTHER end is a single cardan joint. With no canceling mate, you must run it straight as possible, close to 0 degrees but not quite 0 to minimize the rollers from sitting still and pounding into the cup or cross leg.

There's the problem - the transfer case end has a double joint and that takes care of some severe angles - for THAT end.
The other end - you have to rotate the pinion to match the shaft - be able to draw a straight line through the center of the pinion shaft on through the center of the driveshaft.
Front or rear, same thing.

 

[ShadowsPapa]

Okay, now calm the hell down and actually SEARCH for what you think is out there.

It isn't made for the JL/JT platform. There is no TRUE CV joint, all the CV joints you'll find are double cardan. There is no high angle zreppa.

There is no other option, short of custom ordering (you think what's out there is expensive) exactly what you want, and no one offers a warranty for a zreppa high angle for the JL/JT.

You need to get out of your perfect world laboratory and actually search for some of the things you preach.

I know what's out there - that's the problem. All of the shaft vendors are making only shafts with the single joint - and that means you have to rotate the axle housing to line up with the shaft.
I know that. I never said there was anything else - other than stock type shafts.
Double cardan aren't true CV joints - as the guy in that video says.

Yes, there are Jeep rzeppa (it's rzeppa) joints that will go to 15 degrees.
Some larger will do 20-50. (front axle)

Yes, there are performance shafts made with rzeppa joints. But again, people choose the cardan due to ease of trail repairs - so there's little demand. (but they DO exist for JK.......)


You seem to believe I don't know this stuff.

I originally started out trying to explain why the OP is getting vibration now that he has take out the stock drive shaft and put in this "performance" shaft (and I use the word "performance loosely)
It's because of the angle of that single joint.
I posted explanations, and videos to demonstrate what I was talking about.

To fix his issue, he's got to go with a different shaft type or take out caster.
Those are the only two choices.
You can't run a single cardan joint with that much angle and not get vibrations.

And suddenly - it's derailed.

 

[kevman65]

I can't believe driveshaft makers put a single joint at the differential end of the shaft. It just boggles the mind. That end should have a CV joint since yo have to run the shaft uphill to the transfer case, and those with lifts often run heavy caster, meaning the pinion is tipped down, while the transfer case is lifted up farther from the pinion of the front axle.
What the heck is up with that?



A properly designed front shaft should have a double joint, or a CV, at the pinion end to take care of the extra caster, or downward tilt of the pinion, and the increased angle to the transfer case due to lifts.
IMO, it's a pissy design.

Physically, a real CV will handle the power fine, and work higher angles, and not be prone to any vibration because - well, CV is constant velocity. And gee, I've been talking about shaft velocity this whole time and how that vibration is the constant changing of the rotational speed of the pinion.

These are the points you tried to make earlier, I've tried to show you, they don't exist and the people who designed/engineered/built our drive train design all of theirs the way they are too.

You can say all day long it should be something else. But in your own famous words, "The engineers know better than we do".

Almost every rig out there that bounces off of rocks and goes desert running AND is street legal, is running THIS set up.

 

[ShadowsPapa]

Almost every rig out there that bounces off of rocks and goes desert running AND is street legal, is running THIS set up.

Are you including JK? Because almost all vendors sell true high angle CV shafts for the JK

Could be so many run these and don't ask for the CV is because they've believed the wives' tales that the CV is weaker (tests prove it's not)


And you jump in saying I am assuming the transfer case output sits level. Seems to me that's where things took another left turn.

 

[ospreyfe55]

ShadowsPapa,

I want to say thank you helping understand a little better and fully understand. When I worked Helicopters we always had to deal with tail rotor driveshaft and flexing of the tail boom.
I will say I wasn’t aware of all these issues with running this kind of setup. I went with assuming all these companies and the 1000s of shafts out there I figured I would have run into someone wit Khoury these same issues. Unfortunately my lift height has caused my OEM driveshaft beat up the cv joint and tear the rubber along with deform the coupling. So I really didn’t have a lot of options when it came to this issue.

 

[Lunentucker]

Maybe I'm missing something, but here's my take on a subject that I'm really not THAT interested in.


Custom "performance" driveshaft makers are building products that "perform" at low speeds and adverse terrain. They're making products for high lifted vehicles that a have long since left the chat for rolling down the highway at 50 MPH in 4H, because the shady parts are icy.
They're building for crawlers in off-road conditions.

So when people jack their highway vehicles way up, and they get that itch to beef up things like driveshafts, for better "performance", and then are disappointed with how it doesn't do well on the highway at highway speeds, they've moved the definition and expectation of "performance" to somewhere else.

Want a great driving JT again? Go back to stock or maybe a quality 2" lift.

Want to crawl? Then crawl.

 

[Stan H]

Because of the lift, its been tore up for a while and start spinning grease out of the cv boot. Trust me if there were other options then that $800 could have been spent else where.

Why not take the stock unit to a druveshaft shop have a heavier tube and longer tube if needed added to it and fix any other issues such as needed . That's what I would do.

 

[ShadowsPapa]

Maybe I'm missing something, but here's my take on a subject that I'm really not THAT interested in.


Custom "performance" driveshaft makers are building products that "perform" at low speeds and adverse terrain. They're making products for high lifted vehicles that a have long since left the chat for rolling down the highway at 50 MPH in 4H, because the shady parts are icy.
They're building for crawlers in off-road conditions.

So when people jack their highway vehicles way up, and they get that itch to beef up things like driveshafts, for better "performance", and then are disappointed with how it doesn't do well on the highway at highway speeds, they've moved the definition and expectation of "performance" to somewhere else.

Want a great driving JT again? Go back to stock or maybe a quality 2" lift.

Want to crawl? Then crawl.

Bingo.
Can't have both - well, you really can with the CV joint but no one makes one for the JL or JT other than MOPAR or replacements for stock.
If you want that cardan joint up there, you must compromise on street performance - line that pinion up.
Otherwise, use a factory joint if you want the lift and street performance and don't really do the hardcore stuff.
You know a lot of Jeeps lifted to 3" + with 35" tires aren't hitting hard trails - it's the appearance factor. In that case, keep your stock driveshafts or a CV joint.
They'll handle heavy angles and are absolutely as strong, just not as handy on the harsh trails due to the dust boot and who wants to fix a CV joint on the trail? No takers?

 

[Jteakus]

To get your d/s angle where it won't vibrate at speed and have your caster where you want (need) it you would need to grind the welds on your inner C's, roll your pinion up to the correct angle to make the joint angles happy, set your caster then burn the C's back in.

 

[ShadowsPapa]

To get your d/s angle where it won't vibrate at speed and have your caster where you want (need) it you would need to grind the welds on your inner C's, roll your pinion up to the correct angle to make the joint angles happy, set your caster then burn the C's back in.

perhaps just a teeny bit outside of the scope of most DIYers, maybe?

 

[Jteakus]

Perhaps.

 

[Wheelin98TJ]

These are the points you tried to make earlier, I've tried to show you, they don't exist and the people who designed/engineered/built our drive train design all of theirs the way they are too.

You can say all day long it should be something else. But in your own famous words, "The engineers know better than we do".

Almost every rig out there that bounces off of rocks and goes desert running AND is street legal, is running THIS set up.

Every YJ, TJ, and XJ left the factory with a front driveshaft that has a double cardan joint at the t-case and a single u-joint at the front axle. And nobody was swapping in double cardan both ends driveshafts.

As I said earlier, it’s rare you need double cardan on both ends. Maybe if you have a pinion and t-case output that are offset and it’s offset by a lot. More than the popular 8.8 swap cause those didn’t need double cardan both ends either.

 

[ShadowsPapa]

Every YJ, TJ, and XJ left the factory with a front driveshaft that has a double cardan joint at the t-case and a single u-joint at the front axle. And nobody was swapping in double cardan both ends driveshafts.

As I said earlier, it’s rare you need double cardan on both ends. Maybe if you have a pinion and t-case output that are offset and it’s offset by a lot. More than the popular 8.8 swap cause those didn’t need double cardan both ends either.

Fine for factory caster, factory height and not driving over 20 or so in 4 wheel drive.

In each case I've helped, the solution was to line the pinion up with the drive shaft. A couple were rear shafts with pretty decent lifts, others were front.
If you notice, even the vendor said they were doing the same thing - changing pinion angle to match the drive shaft.
One I worked with for the rear shaft vibration is a forum member. Otherwise, it's been others.
So you either line up the pinion - get rid of some caster, or you use a different shaft.
Note that the factory shaft has a CV joint at the transfer case due to the canting of the front t-case output putting a greater angle on the joint. A cardan joint would not cut it on the rear of the front driveshaft even from the factory because of the angle.
The front end of the factory shaft is a single cardan joint - running very nearly straight at stock height and stock caster.
A 2" lift isn't going to change that angle a whole lot - still inside the range of angles where the vibration will be minimal or not noticed.
But when you add caster and a higher lift, now you put that single joint at such an angle at speeds above a certain point, it's going to be a bad vibration.

doesn't matter what others came with from the factory because those were running minimal angles from the factory and likely not seeing high speeds in 4 wheel drive.
The effect is greater with greater angle and greater speed.

The OP is not the first person I've talked about this issue with, not the first person I have helped or tried to help - and again, notice that even the VENDOR! is saying "get rid of some caster (meaning they are telling him to reduce that angle)

I've been through this sort of thing several times over the years, and again, even with a forum member who ended up tilting the pinion to match the shaft. Vibration gone.
It doesn't matter a lick if it's a front shaft or rear shaft, the only difference is that with a front shaft, many people are getting by or putting up with it because it's only a bother in 4 wheel drive and at some speeds, probably over 20 mph, because it's shaft RPM that amplifies it into a vibration.
geometry, science.

Jeep did what they did because they could.
As far as that goes - most vendors sell front drive shafts for lifted JKs with a CV front joint.
I wonder why.........

 

[JTenn]

These so-called performance shafts, which IMO, is highway robbery for the prices, force people to compromise to be able to get by with their designs.
I say "get by" because it's a severe compromise to have to give up caster, and you still have a cross type joint running a fair angle that isn't any stronger, and in many cases with high angles, far weaker, than a true CV joint.
I guess a person needs to choose parts, and compromises, based on their true intended use.
Sadly, many of these go into Jeeps and trucks that don't see the sort of trail abuse that would justify not going with a true CV.

The one and only advantage of these shafts is that you can carry a spare joint in the toolbox and replace it on the trail (unless you mess up the actual shaft or the yoke!)
So if you only bust the joint (because they aren't strong running at severe angles) and need to replace the joint - advantage point to shaft like this. Otherwise, I see none.

Yeah unfortunately for me I am beginning to see this now. Oh well, this is certainly not the first time I've made a purchase of a product that has left me somewhat disappointed. Stronger? Well I really don't know but I can say for sure it's alot bigger and heavier.

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