Calling all TJs with 5.13 gearing (or deeper) that had or currently have vibrations at highway speeds

[freedom_in_4low]

I'm curious what the rpm capabilities are for places like Tom Wood or Adams vs someone like Spicer. My truck (Tacoma), has been regeared from 4.30 to 5.29. My driveshaft speeds are almost 4800 at 80. Absolutely no issues whatsoever. Smooth as glass. Obviously that's a different type of driveshaft, it's a 2 piece with the solid chunk hooked to transfer case, supported by a carrier bearing, and then a normal 4' or so driveshaft from the carrier bearing to the diff. If that can spin at 4800 rpm with no ill effects, it's hard to see why a Jeep driveshaft couldn't.

Of course, then you start getting into the critical speed and using a smaller tubing diameter like the Jeep driveshafts use could make a difference there. I wish I knew what the safe speeds were for the double cardan joint itself.

For the sake of candor, several bits of what I've posted in this thread including the the industry typical 3300rpm and the stuff about using a larger tube are just me regurgitating stuff I've been told by Shawn Wood.

If I remember correctly, the reason TJ shafts are always 2" is because they can machine the female splines into the tube interior to provide the long-travel X-spline. Going larger requires them to use an insert for the female splines so you only get about half the spline length, and his opinion was that any advantage in using a larger tube would likely be negated by losing the extra spline engagement. There's also some doubt as to whether the larger tube would actually help anything, because thanks to the short length we're well below the critical speed even with the 2" tube on an LJ. It remains difficult for me to get past every factory shaft (including the TJ) that I've ever seen being larger than 2" but I have nothing scientific to base that on, whatsoever.

Also I have been led to an understanding that in spite of the general perception that a double cardan cancels out the vibrations inherent to u-joints, that it's not a perfect cancellation, so there will be an angle vs speed threshold at which it will still cause vibration. I don't know what that threshold normally is, but since we're feeling two shafts combined, it only takes each DC to be at half that threshold to start bothering us.

 

[bigpapaparker]

I'm curious what the rpm capabilities are for places like Tom Wood or Adams vs someone like Spicer. My truck (Tacoma), has been regeared from 4.30 to 5.29. My driveshaft speeds are almost 4800 at 80. Absolutely no issues whatsoever. Smooth as glass.Hell, I've even had it up to 95-100 once or twice which is more like 5400-5700 driveshaft rpm. Obviously that's a different type of driveshaft, it's a 2 piece with the solid chunk hooked to transfer case, supported by a carrier bearing, and then a normal 4' or so driveshaft from the carrier bearing to the diff. If that can spin at 4800 rpm with no ill effects, it's hard to see why a Jeep driveshaft couldn't.

Of course, then you start getting into the critical speed and using a smaller tubing diameter like the Jeep driveshafts use could make a difference there. I wish I knew what the safe speeds were for the double cardan joint itself.

Our issues are from the front double cardan, not the rear. I believe your taco disconnects the front in 2wd, please correct me if not. And i live a handful of hours from Tom woods, my local guys claim Tom woods does 3300 rpm also. But that's from a competitor, so take it for what that's worth.

 

[Blackjack]

I'm curious what the rpm capabilities are for places like Tom Wood or Adams vs someone like Spicer. My truck (Tacoma), has been regeared from 4.30 to 5.29. My driveshaft speeds are almost 4800 at 80. Absolutely no issues whatsoever. Smooth as glass.Hell, I've even had it up to 95-100 once or twice which is more like 5400-5700 driveshaft rpm. Obviously that's a different type of driveshaft, it's a 2 piece with the solid chunk hooked to transfer case, supported by a carrier bearing, and then a normal 4' or so driveshaft from the carrier bearing to the diff. If that can spin at 4800 rpm with no ill effects, it's hard to see why a Jeep driveshaft couldn't.

Of course, then you start getting into the critical speed and using a smaller tubing diameter like the Jeep driveshafts use could make a difference there. I wish I knew what the safe speeds were for the double cardan joint itself.

Critical speed calculator https://spicerparts.com/calculators/critical-speed-rpm-calculator

Thread where @Shawn at Tom Wood's and I talk about vibrations and critical speed https://wranglertjforum.com/threads/drive-shaft-vibrations.63323/

The problem is with the short lengths and the angles that they have to operate in. The double cardan itself has little issue with whatever speeds we are throwing at it. Your Taco though has a significantly longer shaft and much better operating angles so vibrations are going to be less of an issue.

 

[machoheadgames]

Our issues are from the front double cardan, not the rear. I believe your taco disconnects the front in 2wd, please correct me if not. And i live a handful of hours from Tom woods, my local guys claim Tom woods does 3300 rpm also. But that's from a competitor, so take it for what that's worth.

Your issue is the front, but there are tons of Jeep owners with double cardan front and rear with lifts and everything else that have plentiful vibes, and usually moreso when both shafts are bolted up. Yes, the Tacoma does keep the front driveshaft still in 2WD because of the front disconnect. Although I for a while had a 2lo mod where I could put the tcase in 4WD and bypass the front diff actuator, which spun the driveshaft. I could still go full highway speed with no added vibes, but that's a single cardan front shaft that has good angles and stock suspension. So there's no reason for that one to add vibes when spinning.

Unfortunately things tend to get a bit weird with any double cardan and especially mixed with lift when you start running them at decently high speeds. What would really interest me would be to take a stock height TJ/LJ that doesn't vibe in stock form, gear it as low as possible and see if it then vibes at any speed eventually.

 

[freedom_in_4low]

Our issues are from the front double cardan, not the rear. I believe your taco disconnects the front in 2wd, please correct me if not. And i live a handful of hours from Tom woods, my local guys claim Tom woods does 3300 rpm also. But that's from a competitor, so take it for what that's worth.

TW confirmed to me that they do 3300, and I don't know Toyotas that well but I think there's a decent chance you're right that the front doesn't spin due to a disconnect of some sort.

However, I'll disagree (possibly just semantics) that our issues come specifically from the front and not the rear. I believe it probably comes from them both at the same time, because they likely are both independently within industry accepted tolerances but combine into something perceptible.

 

[freedom_in_4low]

Your issue is the front, but there are tons of Jeep owners with double cardan front and rear with lifts and everything else that have plentiful vibes, and usually moreso when both shafts are bolted up. Yes, the Tacoma does keep the front driveshaft still in 2WD because of the front disconnect. Although I for a while had a 2lo mod where I could put the tcase in 4WD and bypass the front diff actuator, which spun the driveshaft. I could still go full highway speed with no added vibes, but that's a single cardan front shaft that has good angles and stock suspension. So there's no reason for that one to add vibes when spinning.

Unfortunately things tend to get a bit weird with any double cardan and especially mixed with lift when you start running them at decently high speeds. What would really interest me would be to take a stock height TJ/LJ that doesn't vibe in stock form, gear it as low as possible and see if it then vibes at any speed eventually.

All we need is somebody starting on their build willing to do the regear first and get through enough of the break-in to run highway speeds on stock tires.


...but it also has to be a Jeep that DOES end up with vibes when it's all done so we know when in the process they started, so we also need a palantir.

 

[machoheadgames]

Critical speed calculator https://spicerparts.com/calculators/critical-speed-rpm-calculator

Thread where @Shawn at Tom Wood's and I talk about vibrations and critical speed https://wranglertjforum.com/threads/drive-shaft-vibrations.63323/

The problem is with the short lengths and the angles that they have to operate in. The double cardan itself has little issue with whatever speeds we are throwing at it. Your Taco though has a significantly longer shaft and much better operating angles so vibrations are going to be less of an issue.

Yeah I get that, I've played with the calculator some in the past. Just seems like surely there would be a way to make one that can handle vibes better, though I suppose maybe there are downsides like the spline issue freedom mention.

 

[bigpapaparker]

Yes, you're right. My vibes are from the front , i did not mean to speak for the masses. I did do the gears before lift and tires, but only drove it long enough to break them in, and all at lower, sub 60 mph speeds. And with the little tires true speed at about 60 mph rpm was really high in od. So i wish i could speak more to the lift being the deciding factor. But i can not.

 

[NOTNSUV]

Without reading the entire thread (I spent many hours on the "old" ones) I'll give you my experience.

35s/TT/1"MML/4.5" RE/aftermarket driveshafts.
TJUR 06, 4.0/6spd

Geared from 4.10 to 5.13
Got the oscillation. Took it to the driveline shop who did the gears, he spun front shaft to 3700rpm, balanced it and now very smooth - dramatic improvement.
For shits 'n giggles I subsequently pulled the front driveshaft, test drove, and felt/heard no difference.
The lottery ticket I ran and bought didn't work out as well, but it was a great day just the same.

Appreciate y'all not calling BS on my 3700rpm statement.
Just off the phone with SLY and he confirmed 3300 is max he can do w/o spending a ton of cash for a higher speed machine. Apparently, I mis-heard.

So, apologies for the mis/dis.

Now I feel double lucky to have had it resolved.

Rock on!

 

[Ericshere03]

I had vibes on a 5.13 geared automatic rubicon … I just sent it in to be balance and problem solved … this was a factory driveshaft with 20k miles on it.

Seeing that balance is the issue, you gotta remember that driveshafts have critical RPMs where their elasticity will cause a vibration after a certain RPM. Bigger the diameter the bigger the RPM the shaft can take (length also plays a part, as well as tube thickness and material) … our driveshafts are pretty thin and we spin them pretty high when geared.

I always thought that perhaps a little oil thrown in the tube before welding up would work as a damper and dynamic balance …

Bottom line, balance is critical! Especially on the longer front shaft

 

[freedom_in_4low]

Yeah I get that, I've played with the calculator some in the past. Just seems like surely there would be a way to make one that can handle vibes better, though I suppose maybe there are downsides like the spline issue freedom mention.

We know the rzeppa joints used in JKs don't work, but that doesn't necessarily condemn the concept altogether. Maybe we just need someone to manufacturer a beefier one that can take the angles we work with.

Mine isn't even that extreme...maybe 14deg total. TJs are a lot worse, yet there doesn't seem to be any increased propensity due to the extra angle.

 

[Shawn at Tom Wood's]

This topic has been discussed extensively but sure, lets beat the dead horse a little more. Here are some things to consider.

• Most of the time TJs work fine with 5.xx gears. Gearing extra low doesn't guarantee high speed vibrations but it does increase the probability of high speed vibrations.
• Nothing is perfectly balanced. The smallest weight we can get is 0.14 ounce. https://neapcoparts.com/dlw-1-driveshaft-weight/. Other factors contribute to the level of perfection that is achievable as well but for now lets just assume that we can only add weight in the increments of .14 ounces or more.
• The bigger the diameter a shaft is the faster the surface speed is and the greater the force of the balance weight will be. Critical speed is important to consider when ensuring that the shaft is not flexing at high speeds but generally speaking in a TJ critical speed is a non-issue. Which means that keeping the diameter small is actually advantageous as it minimizes the centrifugal force of any imbalances.
• The equation to calculate centrifugal force is F = m v² / r. I'm not smart enough to do it manually so I use the calculator linked above. However, I am smart enough to know that the little number 2 in that equation is important, it means squared. It tells us that as speed doubles the force quadruples. Just as 4² = 16 and 8² = 64, the base number doubles but the squared number quadruples. Same applies to the force of an imbalance. This is important to note because the effect of going from 3,500 rpm to 4,000 rpm, a 500 rpm increase is far greater of a change in force than going from 2,500 to 3,000 rpm even though it is also just a change of 500. The faster the shaft is spinning the more a couple hundred more rpm will affect the force of imbalances and thus vibrations.
• I've run the calculations for how much force this tiny weight creates, which is about the diameter of a nickel but not as thick, using the force calculator on this page https://www.omnicalculator.com/physics/centrifugal-force. Remember, it calls for radius so I'm halving the diameters.

Now that I've demonstrated how much force the smallest balance weight can produce at different RPMs I'll explain some of the other factors that cannot be controlled by means of adding balance weight.

• Looseness/slop between drive shaft parts. Moving parts have to move, which means there has to be a tiny amount of clearance between them. Maybe it's only a couple thousandths of an inch. But image the entirety of the mass of the drive shaft shifting to one side and being .005" off-centered. How much of that shaft's weight is off center? As much as one of these small .14 ounce balance weights maybe? So if the moving parts of the drive shaft cause the mass of that drive shaft to shift to one side by a couple thousandths of an inch it can/will impact how smoothly that shaft runs at high speeds. Maybe next time you start up the Jeep the shaft shifts in the opposite direction by the same amount, moving the high side of the imbalance. This creates a moving target that is impossible to counter by adding balance weights.
• How many thousandths of an inch side to side play is there in your transfer case output bearing and your pinion bearing? This movement also causes the centerline of the mass of the drive shaft to shift around in the vehicle.
• Same thing with the centering of the x and y axis on the yokes that the shaft attach to in your vehicle. A $60-$75 transfer case yoke is not machined perfectly to the nearest .0001". Things might be off by a few thousandths of an inch, there are tolerances. Any little bit of off-centeredness in the yoke, where the joint sits, is going to make the drive shaft run a little bit off centered.
• Also, those yokes are cast before they are machined but much of the profile of the yoke is still a casting. Casting is literally pouring molten metal into sand so it stands to reason that the casting might be a half ounce, or more, thicker or heavier on one side than the other, adding to the aggregate mass of imbalance of the drive shaft as it is spinning at the same speed at the shaft and attached directly to the shaft. The transfer case and pinion yokes are not dynamically balanced parts.

The point I'm trying to make here is that there are so many nuanced little things that by themselves might not cause a noticeable vibration but as a whole can and sometimes do. Many of these things cannot be remedied by simply balancing the shaft better or changing the design of the shaft. Laws of physics have limitations. What is possible in manufacturing has limitations. At least unless you have a NASA budget but even then there are still limits, just less limited than what you're going to find available for your Jeep currently. Vibrations are inherent, they are present in anything that is in motion, even in things that aren't in motion if you want to get real brainy. Gearing low (numerically high) increases the speed of the drive shaft, thus increasing the intensity of force of those rotating objects, and therefor the perceptibility of vibrations, in a quadratic (think exponential) manner and not in a linear manner. Every action has a reaction, every change you make to your Jeep affects something else.

 

[freedom_in_4low]

This topic has been discussed extensively but sure, lets beat the dead horse a little more. Here are some things to consider.

• Most of the time TJs work fine with 5.xx gears. Gearing extra low doesn't guarantee high speed vibrations but it does increase the probability of high speed vibrations.
• Nothing is perfectly balanced. The smallest weight we can get is 0.14 ounce. https://neapcoparts.com/dlw-1-driveshaft-weight/. Other factors contribute to the level of perfection that is achievable as well but for now lets just assume that we can only add weight in the increments of .14 ounces or more.
• The bigger the diameter a shaft is the faster the surface speed is and the greater the force of the balance weight will be. Critical speed is important to consider when ensuring that the shaft is not flexing at high speeds but generally speaking in a TJ critical speed is a non-issue. Which means that keeping the diameter small is actually advantageous as it minimizes the centrifugal force of any imbalances.
• The equation to calculate centrifugal force is F = m v² / r. I'm not smart enough to do it manually so I use the calculator linked above. However, I am smart enough to know that the little number 2 in that equation is important, it means squared. It tells us that as speed doubles the force quadruples. Just as 4² = 16 and 8² = 64, the base number doubles but the squared number quadruples. Same applies to the force of an imbalance. This is important to note because the effect of going from 3,500 rpm to 4,000 rpm, a 500 rpm increase is far greater of a change in force than going from 2,500 to 3,000 rpm even though it is also just a change of 500. The faster the shaft is spinning the more a couple hundred more rpm will affect the force of imbalances and thus vibrations.
• I've run the calculations for how much force this tiny weight creates, which is about the diameter of a nickel but not as thick, using the force calculator on this page https://www.omnicalculator.com/physics/centrifugal-force. Remember, it calls for radius so I'm halving the diameters.

View attachment 464723

Now that I've demonstrated how much force the smallest balance weight can produce at different RPMs I'll explain some of the other factors that cannot be controlled by means of adding balance weight.

• Looseness/slop between drive shaft parts. Moving parts have to move, which means there has to be a tiny amount of clearance between them. Maybe it's only a couple thousandths of an inch. But image the entirety of the mass of the drive shaft shifting to one side and being .005" off-centered. How much of that shaft's weight is off center? As much as one of these small .14 ounce balance weights maybe? So if the moving parts of the drive shaft cause the mass of that drive shaft to shift to one side by a couple thousandths of an inch it can/will impact how smoothly that shaft runs at high speeds. Maybe next time you start up the Jeep the shaft shifts in the opposite direction by the same amount, moving the high side of the imbalance. This creates a moving target that is impossible to counter by adding balance weights.
• How many thousandths of an inch side to side play is there in your transfer case output bearing and your pinion bearing? This movement also causes the centerline of the mass of the drive shaft to shift around in the vehicle.
• Same thing with the centering of the x and y axis on the yokes that the shaft attach to in your vehicle. A $60-$75 transfer case yoke is not machined perfectly to the nearest .0001". Things might be off by a few thousandths of an inch, there are tolerances. Any little bit of off-centeredness in the yoke, where the joint sits, is going to make the drive shaft run a little bit off centered.
• Also, those yokes are cast before they are machined but much of the profile of the yoke is still a casting. Casting is literally pouring molten metal into sand so it stands to reason that the casting might be a half ounce, or more, thicker or heavier on one side than the other, adding to the aggregate mass of imbalance of the drive shaft as it is spinning at the same speed at the shaft and attached directly to the shaft. The transfer case and pinion yokes are not dynamically balanced parts.

The point I'm trying to make here is that there are so many nuanced little things that by themselves might not cause a noticeable vibration but as a whole can and sometimes do. Many of these things cannot be remedied by simply balancing the shaft better or changing the design of the shaft. Laws of physics have limitations. What is possible in manufacturing has limitations. At least unless you have a NASA budget but even then there are still limits, just less limited than what you're going to find available for your Jeep currently. Vibrations are inherent, they are present in anything that is in motion, even in things that aren't in motion if you want to get real brainy. Gearing low (numerically high) increases the speed of the drive shaft, thus increasing the intensity of force of those rotating objects, and therefor the perceptibility of vibrations, in a quadratic (think exponential) manner and not in a linear manner. Every action has a reaction, every change you make to your Jeep affects something else.

Do you lurk here and wait for these posts or do you have a bot that alerts you when they pop up? Haha

I tried to regurgitate some of the things we've talked about without tagging you in hopes that it wouldn't drag you into a another dead-horse-beating. hope I didn't get any of it wrong though.

 

[NskLJ]

I only do single cardan conversion shafts for folks that are building buggies. The tcase output is typically at an angle that trying to make the pinion angle work without modifying the axle housing is not going to work.

I am but this is not my area so I feel like I know just enough to be dangerous. I have a pretty good grasp on balancing something that is more concentrated in a plane, like a fan or pump impeller or even a wheel/tire. But when it comes to a shaft with three sections that spin around 3 different axes (centering yoke, H-yoke, main tube) my head starts hurting and honestly I'm not sure I understand how it can be done without doing each section independently.

One thing I found rather I interesting is when I had a TJ length rear shaft from TW, took it to a local shop to have it lengthened, got it back and had vibes, then sent back to TW to check it out...they said it checked out fine but went ahead and rebalanced it anyway, and it came back with the weight in a different place. I'm not near my jeep to look but one of them put it on the main tube and the other put it on the h-yoke.

Drive shaft can be tricky, not to mention finding a shop that can do the work right and be around the next time you show up. Worked in automotive for years did a lot of NVH concerns not too many driveshafts though. The TJ must be a whole different animal though with the short shaft and steep angles. The only Jeep I have ever owned is my LJ where the wheelbase helps with the driveshaft angles.

 

[bigpapaparker]

well, in my case, I'm not convinced it's a true "vibration" as much as just harmonics created by the entirety. I say that because it comes on around 60, but nearly disappears above 70. 75 mph is quite smooth actually.

 

[Shawn at Tom Wood's]

Do you lurk here and wait for these posts or do you have a bot that alerts you when they pop up? Haha

I tried to regurgitate some of the things we've talked about without tagging you in hopes that it wouldn't drag you into a another dead-horse-beating. hope I didn't get any of it wrong though.

Someone tagged me and I got an email notification. I'm like Beetlejuice, say my name and I might just show up. I check the forum a couple times a month, search the term "driveshaft". I used to check in more but it seems that a lot of the questions people have about drive shafts have been answered and most of those babies have been put to bed. That and I've created more videos and tech pages on our website that come up in google searches so people don't have to ask the forums quite as much. I'm happy to be here and I like contributing to the conversation and sharing what knowledge I have. I don't think you got anything wrong in your posts, I hope I didn't either! When I refer to beating a dead horse I think what I mean by that is that there isn't some magic secret of engineering that we're going to uncover that will eliminate the possibility of high speed vibrations after re-gearing. So in my mind the conversation is more about explaining why those vibrations are a possibility instead of trying to figure how to prevent or cure them. That part is simple, don't lift your jeep, don't re-gear, don't drive above 65.

 

[Shawn at Tom Wood's]

well, in my case, I'm not convinced it's a true "vibration" as much as just harmonics created by the entirety. I say that because it comes on around 60, but nearly disappears above 70. 75 mph is quite smooth actually.

This. Everything that's moving is vibrating, those things are going to sync up and harmonize at certain points. That's the hard part for us, we can't make a drive shaft that makes everything else stop vibrating or making noise. There's so many different things that can and do contribute to vibrations and the drive shaft is often the scapegoat. But in reality it is just a member of a much larger orchestra. That being said, sometimes the drive shaft is the loudest player so to speak.

 

[Blackjack]

Our issues are from the front double cardan, not the rear. I believe your taco disconnects the front in 2wd, please correct me if not. And i live a handful of hours from Tom woods, my local guys claim Tom woods does 3300 rpm also. But that's from a competitor, so take it for what that's worth.

Assuming the shaft is in good working order it is not the issue. The issue is with the circumstances we have asked it to operate in.

 

[Blackjack]

TW confirmed to me that they do 3300, and I don't know Toyotas that well but I think there's a decent chance you're right that the front doesn't spin due to a disconnect of some sort.

However, I'll disagree (possibly just semantics) that our issues come specifically from the front and not the rear. I believe it probably comes from them both at the same time, because they likely are both independently within industry accepted tolerances but combine into something perceptible.

You are not wrong. It could be the front, rear or both it just depends on the circumstances.

 

[Blackjack]

Yeah I get that, I've played with the calculator some in the past. Just seems like surely there would be a way to make one that can handle vibes better, though I suppose maybe there are downsides like the spline issue freedom mention.

You are looking at it somewhat the wrong way. The shaft is only one part of the equation.

We know the rzeppa joints used in JKs don't work, but that doesn't necessarily condemn the concept altogether. Maybe we just need someone to manufacturer a beefier one that can take the angles we work with.

Mine isn't even that extreme...maybe 14deg total. TJs are a lot worse, yet there doesn't seem to be any increased propensity due to the extra angle.

Actually rzeppa joints do work but they have angle limitations without suffering boot failure.

I had vibes on a 5.13 geared automatic rubicon … I just sent it in to be balance and problem solved … this was a factory driveshaft with 20k miles on it.

Seeing that balance is the issue, you gotta remember that driveshafts have critical RPMs where their elasticity will cause a vibration after a certain RPM. Bigger the diameter the bigger the RPM the shaft can take (length also plays a part, as well as tube thickness and material) … our driveshafts are pretty thin and we spin them pretty high when geared.

I always thought that perhaps a little oil thrown in the tube before welding up would work as a damper and dynamic balance …

Bottom line, balance is critical! Especially on the longer front shaft

While a shaft that was out of balance was your issue it is not always the case for others.

Unless you are running 29 inch tires and 5.38 gears there is little chance of having a critical speed issues with TJ shafts.

Lots of different things are being used by the OEMs just like the harmonic damper on the back of the late model 231 and 241s. The problem with all this is they add complexity and cost. The correct answer is to try and address underlying issues that are leading to the vibrations as best as we can.