Doesn't the NV241OR result in a shorter driveshaft when compared to a SYE 231? For example, I bet my 231 with the JB conversion super short SYE is much shorter than the NV241OR with its fixed yoke. So the driveshaft is longer with the 231, resulting in better driveline angles? That is the only thing I can think of.
4.0, 42RLE, NP241OR High Speed Vibrations After Re-Gear to 4.88 or Deeper
- Thread starter Mr. Bills
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Doesn't the NV241OR result in a shorter driveshaft when compared to a SYE 231? For example, I bet my 231 with the JB conversion super short SYE is much shorter than the NV241OR with its fixed yoke. So the driveshaft is longer with the 231, resulting in better driveline angles? That is the only thing I can think of.
I'm not 100% sure, but I believe it does result in a slightly shorter rear driveshaft (not sure about the front though). But you're right, that's also the only thing I can think of as well.
I think the real relation here is as you said... the 42RLE requires much deeper gearing, thus resulting in the driveshafts spinning much faster than they would on a different transmission.
Nah I am not being scientific or anything. Just was thinking the opposite. You are probably right but I am trying to wrap my head around it.
It seems reading though though that there are at least two LJR's experiencing the issue, so I doubt it's due to a shorter rear driveshaft length.
Well if the front driveshaft is the cause of the problem, I guess the rear driveshaft angles/length don't matter...
Hmmm, I wonder if the NV241 is mounted differently due to its size. A different mounting position may result in a worse front driveshaft angle...? If the transfer case was tipped backwards a bit or something like that...? I'm actually not sure.
Yep, if that's the case, I doubt it's related to the driveshaft length.
I keep thinking is it's got to be an issue with the driveshaft being out of balanced. I mean whoever is balancing it would have to spin that thing up to 70 mph (or something very fast) in order to know for sure. Because I could see how if it was just slightly out of balance, you might not be able to notice that when it's spinning at a lower speed.
I'm not familiar with how they balance a driveshaft though, so I don't know the process.
You know what would be interesting... if we could get one of these Jeeps up on a rack and take it up to 70 mph while standing under it and watching the front driveshaft. I'm wondering if you could actually visually see anything. If you could, that would be very, very telling.
Xposure
TJ Enthusiast
Yes but that’s a insignificant amount and a rpm that you typically drive anyway. For instance let’s say you get a bigger tire without changing gears your engine rpm goes down or if you go from 3.07 to 4.56 your engine rpm goes up (if you don’t change tire size). But in either case if I’m now cruising as say 2500 or 2700 or 3200 engine rpm the driveshaft is still turning the same as it always has at that given engine rpm and those are all rpm’s your used to driving and that your Jeep was designed for.
The BIG differences is in the rotational speed of the differential itself and axles (when you go from say 3.07 to 4.88)
It isn't an insignificant amount of rpm. It is exactly the ratio between the new gear and the old gear.
For example: If you regear from 1 to 2, your engine speed will increase by a multiple of 2. Therefore the input to the transmission will increase by a factor of 2. Therefore the driveshaft speed will increase by a factor of 2. Play around with grimjeeper. You'll see that if you regear from 4.88 to 5.38, your engine speed will increase by roughly 10% for a given speed and tire size.
The fact of the matter is that the driveshaft speed does increase. If the tires are rotating at X rpm and they are mechanically linked to the driveshaft at a ratio that is the differential gear, the driveshaft rotates at dif-gear * X. Therefore the driveshaft must increase speed when you regear. If the driveshaft didn't increase in speed, then you would just be going slower. Forget about the engine and transmission entirely. They are irrelevant for this scenario.
How can the gears spin faster but not the drive shaft that is connected to them?
@Chris Since you are worried about driveshaft balance, I would ask Tom at what RPM he balances his driveshafts. From some quick math, it appears your driveshaft is spinning at 3616.81 RPM when you are going 70 MPH (with 35 inch tires and 5.38's). That should give some insight as to what 70 mph means in terms of driveshaft speed. My junky Adams driveshaft spins at 3200 RPM when I drive 70 MPH (33" and 4.56's). I'm not sure how much that helps...
(Also, only 90% sure my math was right so please check it...)
He has what differential gears do backwards. He thinks they multiply driveshaft rpm when they really divide driveshaft RPM.
In his mind, axle shafts rotate at, for example, 5.38 * driveshaft RPM. So if you go from 3.07 to 4.56, the axle shafts rotate faster for a given driveshaft RPM. Obviously this isn't the case because that isn't how differential gears work.
(Also, only 90% sure my math was right so please check it...)
He has what differential gears do backwards. He thinks they multiply driveshaft rpm when they really divide driveshaft RPM.
In his mind, axle shafts rotate at, for example, 5.38 * driveshaft RPM. So if you go from 3.07 to 4.56, the axle shafts rotate faster for a given driveshaft RPM. Obviously this isn't the case because that isn't how differential gears work.
I just noticed this and figured I’d mention I ran into the same issue when I rebuilt my np231. Had to do quite a bit of searching to find rpm ratings for the bearings that came in the rebuild kit. Even with a bearing rated for double the rpm range, it didn’t completely solve my driveline vibes but it did help considerably. I still have some minor vibes at highway speeds, but nowhere near as bad as what I started with after a regear to 4:56’s. I’m convinced the tolerances in my transfer case are just too big for the rpm’s it’s seeing after the gear swap. Here’s the post:
https://wranglertjforum.com/threads...bration-above-50-mph.4235/page-14#post-134972
Very interesting, thanks for sharing this. And here's the link to the bearing in question for anyone who is wondering:
https://www.amazon.com/dp/B007EDPEK2/?tag=wranglerorg-20
So this is the bearing that the shaft on the transfer case spins on, correct? I wonder if it's the same size bearing for the NP241OR.
It’s the front output shaft inner bearing if I recall correctly. The outer bearing (closest to the yoke) is a ball type bearing. The inner bearing is pressed into the back side of the t case housing and it’s a needle style. My output shaft had vertical play like it was see-sawing using the outer bearing as a pivot point. I rebuilt the t-case but the bearing that came in the kit just seemed cheap and didn’t fix the play I was having. Measured the output shaft bearing surfaces and they were good, so it didn’t seem to be a worn shaft. Upgraded to the 8600rpm bearing and it tightened things up, but there’s still a tiny bit of play. I haven’t thrown a dial indicator on there to quantify how much “tiny” is, but it’s enough that you can feel it clicking up and down.
I don’t think this is a solution for all of these vibe issues I keep reading about, but in my case it was certainly a factor.
I agree that this may not be a solution, but it's certainly something that should be looked at.
I wonder if the pinion yoke bearings could be a cause of these vibrations as well.
I like this discussion. I am excited to find out what @David Kishpaugh finds. By the way the subject is mostly auto's but I want to officially add me as a AX15
I am not positive i do, I do have a more of a vibration after the gears, but I did a lot of other work at the same time plus I could degree my axles a little better too. I may be jumping the gun, but if @David Kishpaugh rebuilds and balances your driveline and it fixes your issue, then I am surely going to have Tom Woods build me a new one for sure.
Here's an interesting thought: What do both driveshafts have in common? The transfer case.
This makes me wonder if maybe the bearings that the transfer case output shafts / yokes are spinning on simply can't handle the huge increase in RPMs. It seems like it could be a possibility, no?
This makes me wonder if maybe the bearings that the transfer case output shafts / yokes are spinning on simply can't handle the huge increase in RPMs. It seems like it could be a possibility, no?
Would this test work?
Disconnect both driveshafts at the transfer case. Then put the transfer case in 4 wheel drive high. Then put it in drive and go through the gears until you hit highway speeds. I'm not sure how an automatic would work in this scenario or if it would even shift... In a manual, you could simply put it in 5th and rev up to 3,000 RPM. That would spin the both yokes on the transfer case at highway speeds while the Jeep is stationary. If the vibration is still there, then the transfer case is the problem. If it isn't, then the driveshaft must be the problem.
Then again, I feel like the weight of the driveshaft and the resistance of the tires must have some sort of effect on the transfer case.
Correct. To calculate driveshaft rpm; engine rpm/final drive ratio.
NSG370 for example: 3000 rpm * 4.46 (1st gear) = 13380 rpm driveshaft speed. 3000 rpm * 1.00 (final drive) = 3000 rpm ds speed.
The gear ratio matters since the rpms are increasing at a greater rate the lower you get. Using my own TJ as the example; 4.88/31's is 3100 at 70 mph so 3100 rpm at the ds. Before the re-gear I was at 2400 at 70, so 2400 rpm ds speed. I have a 700 rpm increase at the ds with the gear change.
When you get into OD gears, the engine rpm decreases but the ds speed stays the same.
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