Calling all TJs with 5.13 gearing (or deeper) that had or currently have vibrations at highway speeds
- Thread starter justjake843
- Start date
I regeared significantly lower than stock, seems like quite a few others do too. But yes, otherwise I do agree. If regear keeps you in the stock rpm ballpark, then all things being equal, you’d have vibes all stock. I think it’s the other factors, lift, brand and build quality of shaft, harmonics, etc combined with such and such driveshaft speed that all add up to make the difference.
The 42rle guys who supposedly have most of these issues aren't spinning much more than a couple hundred rpms more than stock right? I think you're right though.its a combination of factors
A lot of 3.73s (stock 30”) go to 5.13 on 33’s and sometimes 31’s. Those both would net higher rpm than stock. On 33’s & 5.13, at 70 mph that would be 3656 driveshaft rpm vs 2924. 25% increase in that case. Obviously slightly less or more for 35’s or 31’s.
4.10 folks have rubis and 30.5’s stock, then many of them go to 5.38 and 35’s. In this case, they’d go from 3162 driveshaft rpm to 3615. 14% in that case, so not as drastic. But still not negligible either.
It generally is faster than stock speeds because most people don't just target stock engine rpm when they regear; they almost always shoot higher to get more power to turn the bigger tires.
A stock non-rubi with 3.73 gears and 29" tires spins the driveshaft at about 2980rpm at 65mph. The common recommendation of 5.13s for 35s does 3345. With 4.88 (what I have) it's 3180.
I drove mine around with 32s for a few weeks waiting for tires. When I changed tires, the onset of the vibration moved down in speed such that it stayed at exactly the same 3600rpm driveshaft speed. The fact that I don't hit it until 74mph has kept me from buying a hub kit, so far.
Driveshaft balancing equipment usually stops at 3300rpm. While in general, balancing isn't rpm dependent, a force that isn't detectable at a lower speed may reveal itself at a faster one. Since the force due to imbalance increases with the square of speed, a given imbalance will exert 20% more force at 3600rpm than it does at 3300. The oscillating pattern of the vibration suggests that what we're picking up is the additive force from both driveshafts...take that to its conclusion and what it implies is that an imbalance force normally considered acceptable at 3300rpm is being amplified to 240% at 3600.
What I don't have an answer for is why we don't seem to hear in large quantities of stock jeeps with 29/3.73 or stock rubicons starting it at 77-78mph, where they would be hitting 3600rpm. Maybe they just don't get driven that fast, or when they do the owner just assumes that's what a Jeep pushing 80 is supposed to sound/feel like. Maybe the aftermarket driveshaft and the CV angle increase the likelihood that it happens.
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Has anyone tried ditching the front double cardan, doing single on both ends of the front shaft, then just adjust the pinion angle to match the t case output angle? My stock rear shaft is smooth as glass at all speeds. Vibes only come on when i install the front.
Since the force due to imbalance increases with the square of speed, a given imbalance will exert 20% more force at 3600rpm than it does at 3300. The oscillating pattern of the vibration suggests that what we're picking up is the additive force from both driveshafts.
How to say your an engineer without saying your an engineer.
How to say your an engineer without saying your an engineer.
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.
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.
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.
Maybe I need to call around and see if anyone in my area has a machine that will balance up to 3700. From my understanding, the driveshaft balancing equipment industry is heavily dominated by a particular company whose machines top out at 3300, but there could be some smaller players out there that go beyond.
Definitely a small player here. His word was 3700rpm. Regardless, it worked. Good luck.
My 2 local shops maximum was either 3000, or 3300. And a little over a c note to check balance, plus 3 days out.
How to say your an engineer without saying your an engineer.
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.
And he wanted to take it in again to tweek pinion for more improvement but it was so good I passed on it. Maybe another time.
He charged me zero. Maybe cuz he did the R&P regear and BM BBK for me.
SLY Driveline, Elko, NV
That's annoying. The place that lengthened mine only charged me $90 for that, which included a balance.
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.