I’m fighting carsickness-wife drives like an Earnhardt- bent axle flange caused mine.
Please help me solve the oscillating vibration crisis by providing some basic info on your Jeep
- Thread starter freedom_in_4low
- Start date
I'm assuming you are talking about something like this https://www.vibracoustic.com/en/product/nrg-disc-flexible-rubber-couplings/ Could be used, theoretically, but it wouldn't be something that could easily be done. You'd have a hard time finding any drive shaft shops that can build one this way (ourselves included) and you'd have to have a flange for your pinion for the rubber coupling to attach to. This flange, to my knowledge, does not exist for a dana 35 or 44 so you'd have to get a custom pinion flange made. These rubber couplings are becoming more common I think in some newer vehicles but they don't have the same robust reliability as a universal joint. Same goes for Rzeppa CV joints. That's what Jeep decided to put in all their Wranglers starting in 2007 which ironically has been the biggest boost in aftermarket u-joint style drive shafts. The new designs of joints that are meant to reduce vibrations, or maybe just give engineers something to do, work great in stock vehicles. It is when people start making changes to their jeep that the stock drivetrain components fail. Also, a universal joint can run smoothly at a degree or two, no problem. The oscillation is still there but at such a low level that it is unnoticeable and virtually non existent. It is as angle increases that the oscillation increases and people start to notice issues. There's some heady tech info that my dad (Tom Wood) wrote probably 20 years ago that explains the u-joint operation in greater detail here if you are interested https://4xshaft.com/blogs/general-tech-info-articles/driveshaft-angles.
This is the country where we take square bread, round meat, diced onions, sliced tomatoes and lettuce leaves, stack it together and cut it diagonally- then complain it falls apart.
I really do marvel at the amount of changes to stock design the aftermarket creates. A good bit of this forum is how to alter these, and then how to fix the consequences.
I’m guilty as they come.
Why are they not called + joints or x joints? We need to work on that too. They aren’t at all u shaped. They could be Ewe joints if we put ‘em on sheep.
Sort of off topic, but this principle is actually the principle used to detect gravity waves. Basically, a device called an interferometer is used to measure incredibly tiny deviations in the length of a given space. Take a laser, break the beam into two dimensions. Merge the beam again, and tune the distance until the resultant beam is at maximum intensity. If one leg changes length relative to another, even on the order of a nanometer over a mile, you can visibly see the result as the resultant light gets dimmer and brighter as the space we occupy literally changes size. With this, we can literally see the gravity wave effects of black holes merging somewhere millions of light-years away, with surprising frequency.
Back on topic, I do agree on your assumption that it isn’t necessarily the shafts vibrating that we feel. That vibration may be sourced in the shaft, but it has to come out somewhere. There are probably quite a few ways to mitigate it without fixing the source issue. Change the mass of the shafts. Add a tuned mass damper, just like the harmonic balancer on the front of our engines. Further isolate the driveline from the body and frame. As to what the ideal solution is, that really depends on how we define the problem. Is the vibration just a problem because it annoys the user? Does the vibration significantly shorten the life of driveline components, and if so, do we care? How much of a problem is it?
To me, I care less about the feeling of the vibrations, and more about the increased wear of the driveline components. So I’m willing to invest a good amount of time and money trying to fix the vibration as it exists in the driveline itself. But I’m not willing to spend more than it would cost to simply just keep replacing components at a faster rate.
My opinion of this problem is that if economically feasible, it should be fixed at the source. But it may require us to shed our love of double cardan driveshafts in favor of something new. Perhaps double-double cardan shafts. Or even true CV shafts.
Or maybe there is a solution that could reduce it to tolerable levels. Aluminum driveshafts are becoming far more popular. Reduce rotational inertia, and perhaps we could reduce the torque required to accelerate and decelerate components through a revolution. Perhaps it might even change the torsional mass-spring-damper equation enough to eliminate problem vibrations. Heck, a possible solution might even be to just stick a big flywheel on the shaft to make the mass so high that the critical frequencies drop below a problem range.
1. Yes, 47-50
2. Not Tested
3. 2002 TJ
4. 44's, 4.10
5. 33
6. 32rh
7. 231 SYE
8. Stock
9. Stock
10. 4"
11. None
2. Not Tested
3. 2002 TJ
4. 44's, 4.10
5. 33
6. 32rh
7. 231 SYE
8. Stock
9. Stock
10. 4"
11. None
1. Do you have the oscillating vibration issue and at what speed does it start?
No
2. does it persist even with the front driveshaft removed?
N/A
3. Model year and TJ or LJ
2005 Unlimited Rubicon
4. Axles and Gear ratio (and if you have a Rubicon, did you keep thick cut gears or did you get a 3.92+ carrier and go to standard gears?)
Stock Rubicon Axles and Lockers, 4.10 (or 4.11, depending upon who you ask)
5. Tire size
285/75-16
6. transmission
NSG370 6-speed
7. transfer case, and if 231, is it SYE'd
Stock Rubicon NVG241OR
8. stock or aftermarket transfer case skid, and if aftermarket, which skid (please include brand, tuck height, and material)
Rubicon Express Long-Arm
9. stock or aftermarket gas tank skid, and if aftermarket, which skid?
Stock skid
10. suspension lift height, if any
3.5"
11. any other mods that might change the way the frame is constrained, such as a stretch, midarm, rear frame raise, crossmember deletions, spring perch relocations, shock outboard, etc.
See #8's response
No
2. does it persist even with the front driveshaft removed?
N/A
3. Model year and TJ or LJ
2005 Unlimited Rubicon
4. Axles and Gear ratio (and if you have a Rubicon, did you keep thick cut gears or did you get a 3.92+ carrier and go to standard gears?)
Stock Rubicon Axles and Lockers, 4.10 (or 4.11, depending upon who you ask)
5. Tire size
285/75-16
6. transmission
NSG370 6-speed
7. transfer case, and if 231, is it SYE'd
Stock Rubicon NVG241OR
8. stock or aftermarket transfer case skid, and if aftermarket, which skid (please include brand, tuck height, and material)
Rubicon Express Long-Arm
9. stock or aftermarket gas tank skid, and if aftermarket, which skid?
Stock skid
10. suspension lift height, if any
3.5"
11. any other mods that might change the way the frame is constrained, such as a stretch, midarm, rear frame raise, crossmember deletions, spring perch relocations, shock outboard, etc.
See #8's response
Jeep decided to put a harmonic balancer on the end of the transfer case output for a reason. Any of us that had that option know it was a pain to remove when changing to a SYE. My guess is that Jeep engineers were trying to figure out a vibration, and the balancer was just enough to get it by testing. I could be way off base here.
That is some interesting information, thanks. Those articles were especially useful as I began learning about some of this stuff.
My assumption is that the root cause isn’t actually the single-cardan joint in most of these cases. It’s the double cardan joint.
A double cardan joint works by canceling out the rotational anomalies associated with a single cardan joint. By operating them back to back at the same angle, there is virtually no change in speed on either the input or the output side. This eliminates a large number of vibrations in itself.
But the intermediate carrier in the double cardan joint is not subject to that cancellation. It has to accelerate and decelerate twice per rotation. Even though the shafts outside of the DC run at the same speed, the carrier does not. In order for it to accelerate and decelerate, it needs an applied force (or equivalently, it must dump a force somewhere). This force is transmitted down one or both shafts into the next component, and eventually through a component providing a reaction force. If that component is not sufficiently rigid or well damped, it would likely cause vibrations. Most of the time, these are likely not problem vibrations. In the case of the TJ, with the steep angles of especially the rear DC joint, the forces are higher because the DC intermediate carrier has to accelerate significantly more during each rotation. Couple that with the transfer case being located very close to the occupants, and that vibration could become very noticeable.
If this is the case, I would actually expect that a jeep with 1310 DC shafts would vibrate far less than an equivalent jeep with 1350 DC shafts. Not only is the 1310 intermediate carrier lighter, it also has less overall diameter, significantly reducing its rotational inertia. The force it transmits down the shafts will only really be dependent upon the rotational inertia of the intermediate carrier, speed of the shaft, and operating angle of the DC joint.
Such a joint as I pointed out would probably do very little to mitigate the effects of a single cardan joint. Like you said, at 1 degree, the rotational differences are far too small to care about. But it might allow enough compliance to prevent the torsional vibrations caused by the double cardan intermediate carrier from reaching the axle. That said, I do think the bigger issue is those forces entering the transfer case.
Yep. I'm not even saying that things like the flexible couplings are a bad design, just that there are certain things that work well for certain applications. I think of it like a video game where you can choose your characters strength, speed, agility, ect. but you only have so many points to spend. Same with drive shafts, if you are going to increase your strength levels to the moon you are going to have to make sacrifices in smoothness or flexibility or max speed. Same goes for increasing any of the other features, the other things will be sacrificed to some degree. One thing your burger/sandwich analogy makes me think of is what I call the "engineering paradox". This is where people sometimes get super hung up on a minor detail like the dust shield on their stock pinion yoke that's not on the aftermarket yoke. They will say "It just seems like if it wasn't important the engineers wouldn't have put it there, Jeep used it for a reason.". But ironically that same logic doesn't apply to suspension height, tire size, steering geometry, motor output, or any of the other changes a person made to get to the point where they need that new pinion yoke without the dust shield. There is no perfect design and changing one aspect of a complete system ripples outward and necessitates changes in other parts of that system. That ladies and gentleman is why I have a job, ultimately because people want bigger tires and drive shafts are somewhere downstream of that with all the other things required to make bigger tires work well.
U-joint being short for Universal Joint is confusing, u-joint makes you think it must be something similar to a u-turn. What's even more confusing is that we call them cardan joints when using the term double cardan which technically might be better named as a triple cardan because a double cardan shaft actually has 3 cardan joints in total. Even more confusing is that we also call them CVs. Wait, who's on first? I'm lost. English is just as hard as designing a vehicle.
BTW, my rant about modifying Jeeps messing up other things is not about the original question regarding the flexible couplings, which was a good question. Just talking more broadly about how when you start fixing problems which were created as a result of fixing other problems you can often end up chasing your own tail and there are some problems that are best left alone as they are not that big of a problem to begin with.
100%. They built over 300k non-Rubicon TJ's between 2003 and 2006. Even if the damper only cost $10, they would have spent $3 million on those. That doesn't happen unless they're pretty convinced that leaving it out would have cost much more than that in warranty work and customer complaints. And senior management would have to find the argument pretty convincing.
So has anybody seen a damper built into a 1310 CV yoke?
Great post, you could could make a great living at this if you bumped your dad off-
All that said , JK and JL’s included, I bet 80 percent of lift work is for “the look”.
The universal joint has been around a long time (centuries), and there are many names used for them. The term universal joint is ubiquitous (at least in North America) because (if I remember my studies from over three decades ago) Henry Ford called them that, and he created the modern automotive industry. As with many things, the first to successfully mass-market a product generally gets naming rights by default.
Why the double Cardan joint is not called a double u-joint is not something I've heard explained, but if I had to guess, I'd guess that they probably call u-joints Cardan joints in Europe (after all, Cardan is named after the Italian who invented them), and the double-Cardan joint was likely invented by the European automotive industry (just a guess). It's called a double, and not a triple, because there are two Cardan joints (u-joints) connected by coupling yoke (or some other device, depending on the patent.)
Finally, let's talk about CV, or Constant Velocity, joints for a minute. All double Cardan joints are CV joints, but not all CV joints are double Cardan joints. The double Cardan is just one specific type of Cardan joint. One is named after a man (Cardano) and one is named after a concept (CV means the input and output shafts don't accelerate and decelerate with each rotation.)
I'm sure Shawn knows most of this stuff, but I bring it up because it's good information to know if you're building a Jeep. When I was in high school, I thought history was a useless exercise in memorization with no redeemable use because I didn't understand how historical context can lead to enlightenment. Many decades later, I've come to realize that learning some history of how things were named, used, designed, improved-upon, etc. can lead to a better understanding of how to design things. It's good to discuss these things because we can jump ahead in our design process by avoiding pitfalls already discovered and dealt with.
Knowing that a driveshaft and differential pinion shaft should be in line when you're using a double Cardan joint, but not when you're using two u-joints and parallel stub shafts is a good thing, but understanding why puts one on a much higher level of knowledge...
What an American thing to do, take a joint that moves in two directions and over-exaggerate its abilities by calling it "Universal". Certainly more marketable than "wobbly joint" or something like that.
I think this is just because we say what is easiest to say or we say what we've heard other people say. Or maybe double u-joint sounds too much like w-joint?
. We used to primarily refer to double cardans as CVs. With the rising prevalence of Rzeppa type CV joints in Jeeps we now use the term double cardan a lot more just as a matter of differentiation. Like I said, English (language) is hard. The important thing to me is always whether or not both parties agree on or understand the meaning of something. For example if someone asks about a "Double knuckle on their hog's head" I know that they are asking about putting two u-joints a their pinion/differential and not some sort of strange porcine deformity. If we really want to get technical a double cardan is not a true constant velocity (cv) joint but we still call them CVs because they do run at near enough of a constant velocity to get lumped in.
You are absolutely right. When teaching our staff certain processes I like to make sure they understand the desired functional outcome. The better they understand why a thing needs to be done they better they understand how it should be done, context is key.
I'm often impressed at how knowledgeable many of you on these forums are. I know these things because I have to, because is is my job, but many of you who I'll assume are not professionals know more than many of the professionals.
This video is less technical and academic than much of the info discussed on this thread but we created a video explaining the how and why of many of the topics discussed above. We wanted to help clear up some of the confusion around these topics.
1. Yes, starts at 60mph quits a 65 and starts again slightly at 85
2. Yes
3. 2000 TJ
4. 30 and 35 with 4.56
5. 33,12.50 km2
6. New AX15
7. 231 AA sye
8. Stock
9. Stock
10. 4.5"
11. None
2. Yes
3. 2000 TJ
4. 30 and 35 with 4.56
5. 33,12.50 km2
6. New AX15
7. 231 AA sye
8. Stock
9. Stock
10. 4.5"
11. None
Anyone interested in reading about Navy fighting with vibration on North Carolina, South Dakota and Iowa class battleships?
https://dome.mit.edu/bitstream/handle/1721.3/48159/DTMB_1945_0518.pdf?sequence=1https://dome.mit.edu/bitstream/handle/1721.3/48161/DTMB_1948_0547.pdf?sequence=1https://dome.mit.edu/bitstream/handle/1721.3/48148/DTMB_1948_0551.pdf?sequence=1
What Woods said about chasing your own tail has been echoing in my head for the past year now.
Who knows of any offroader from the factory with gear ratio lower than 4.1 ? Maybe there is a reason why 4.1 was as low Jeep decided to go? Do we really need anything lower than 4.1 in axles?
https://dome.mit.edu/bitstream/handle/1721.3/48159/DTMB_1945_0518.pdf?sequence=1https://dome.mit.edu/bitstream/handle/1721.3/48161/DTMB_1948_0547.pdf?sequence=1https://dome.mit.edu/bitstream/handle/1721.3/48148/DTMB_1948_0551.pdf?sequence=1
What Woods said about chasing your own tail has been echoing in my head for the past year now.
Who knows of any offroader from the factory with gear ratio lower than 4.1 ? Maybe there is a reason why 4.1 was as low Jeep decided to go? Do we really need anything lower than 4.1 in axles?
Umm.. there is this vehicle called the Jeep you know, that helped with the war effort of sorts in the 40s. Came with 5.38s from the factory is the rumor.
How about something more realistic that can go faster than 45mph, what about it's subsequent models over the years?Umm.. there is this vehicle called the Jeep you know, that helped with the war effort of sorts in the 40s. Came with 5.38s from the factory is the rumor.
I am clueless, never looked into it.