Please help me solve the oscillating vibration crisis by providing some basic info on your Jeep

[macleanflood]

Unless someone fabricobbled a double doubler out of a single block of steel...a left and right end together with two yokes probably set at 180 degrees...so they didn't need coupled together with a welded shaft.

And I suppose said product doesn't exist for a reason.

-Mac

 

[Shawn at Tom Wood's]

@freedom_in_4low In theory both of your drawings would have the same results. If you have two joints at each end of those pairs of joints (each double cardan) are cancelling each other's oscillations. So joints 1 and 2 cancel each other out and joints 3 and 4 cancel each other. With the double cardan at each end of the shaft, the relationship between each end of the shaft doesn't matter. You could almost view it as two different drive shafts, each with a single joint at each end. Imagine your black line as the transfer case and your red lines the front and rear drive shafts in a vehicle. I've added a 3rd example to your drawing. This example C is more exaggerated and more similar to what we see in those front XJ situations because the transfer case points up away front the drive shaft, the drive shaft slopes down away from it, and the pinion points up towards the transfer case, just not enough for a regular double cardan to work well.

 

[Strizzo]

Resurrecting this thread as I just went to 5.13s and 33s and have the occilating/surging vibration from the front driveshaft. I did some math and at 75mph the driveshaft rpm is close to 4,000. This seems like it could be a challenge for the oem front ds with probably over 100k miles on it between actual driving and flat towing.

Has anyone replaced their oem driveshaft with an aftermarket one and had it fix the issue? I read a comment on one of the Facebook groups recently where someone claimed a new driveshaft was their solution.

I’m debating between having my oem shaft rebuilt and just ordering a new shaft if it has a better chance to knock out the issue.

 

[CMBD]

A new drive shaft might not fix the issue. Stock rebuilt or aftermarket.

The front axle being what it is in these things, you need good caster numbers and good pinion angle for the front drive shaft. But you cant really have both depending on your setup.

 

[freedom_in_4low]

Resurrecting this thread as I just went to 5.13s and 33s and have the occilating/surging vibration from the front driveshaft. I did some math and at 75mph the driveshaft rpm is close to 4,000. This seems like it could be a challenge for the oem front ds with probably over 100k miles on it between actual driving and flat towing.

Has anyone replaced their oem driveshaft with an aftermarket one and had it fix the issue? I read a comment on one of the Facebook groups recently where someone claimed a new driveshaft was their solution.

I’m debating between having my oem shaft rebuilt and just ordering a new shaft if it has a better chance to knock out the issue.

I got a new front shaft and it did not help. I suspect the source of the Facebook claim had a worn shaft to begin with and was experiencing a different issue than most of the folks in this thread.

The vibrations seem to be torsional, not radial. It had been proposed that DC shafts are less ideal due to the larger diameter chunk of mass in the H yoke and that maybe having two on the same vehicle and spinning them close to 4000rpm just isn't ideal. Maybe that's why Jeep never did it from the factory even though traditional logic would say the rear needed it as much or more than the front does due to the length.

 

[Rickyd]

Resurrecting this thread as I just went to 5.13s and 33s and have the occilating/surging vibration from the front driveshaft. I did some math and at 75mph the driveshaft rpm is close to 4,000. This seems like it could be a challenge for the oem front ds with probably over 100k miles on it between actual driving and flat towing.

Has anyone replaced their oem driveshaft with an aftermarket one and had it fix the issue? I read a comment on one of the Facebook groups recently where someone claimed a new driveshaft was their solution.

I’m debating between having my oem shaft rebuilt and just ordering a new shaft if it has a better chance to knock out the issue.

How much play is in the splined slip section? If you can wiggle it perpendicular to the shaft then yes,the driveshaft is worn out and you want a new one

 

[JMT]

Has anyone replaced their oem driveshaft with an aftermarket one and had it fix the issue?

My vibes with OEM shaft came on at 65mph. With aftermarket they moved to 73mph. Better!

 

[Strizzo]

A new drive shaft might not fix the issue. Stock rebuilt or aftermarket.

The front axle being what it is in these things, you need good caster numbers and good pinion angle for the front drive shaft. But you cant really have both depending on your setup.

Thanks, I understand the limitations of the stock axle setup, and I don’t think I’m so far from stock that I can’t get the pinion angle/driveshaft angle correct enough while keeping enough caster, my understanding of the issue is that even perfect pinion angle can’t fully eliminate the surging vibration as it has something to do with multiple vibrations that are going in and out of sync.

The stock DC front has enough miles on it that it would flop down when I was trying to reattach it to the transfer case when I did the sye, so I have a feeling there is some room for improvement there regardless. I also received my double adjustable front arms this weekend and will try to get them on so I can easily mess with the adjustment on the pinion angle and caster.

I got a new front shaft and it did not help. I suspect the source of the Facebook claim had a work shaft to begin with and was experiencing a different issue than most of the folks in this thread.

The vibrations seem to be torsional, not radial. It had been proposed that DC shafts are less ideal due to the larger diameter chunk of mass in the H yoke and that maybe having two on the same vehicle and spinning them close to 4000rpm just isn't ideal. Maybe that's why Jeep never did it from the factory even though traditional logic would say the rear needed it as much or more than the front does due to the length.

I would agree with you on spinning them 4000 rpms, but jeep did use two DC driveshafts on the rubicon models.

I can see where getting the front driveshaft/pinion angle can be a challenge on like a 4" lift, but I feel like i should be able to get mine right enough with only 2.5" of lift. eyeballing it it already looks pretty close, but I'm pretty sure i have more caster than I need at the moment.

Is it a correct assumption that this is not an issue for people running 35s with the 42RLE and 5.13 or higher gears due to the lower driveshaft speeds? that may be the ultimate solution if I can't manage to solve mine.

 

[mrblaine]

I read a comment on one of the Facebook groups recently where someone claimed a new driveshaft was their solution.

In cases where their answer flies in the face of tons of data to the contrary, I make them a simple offer. Fine, I'll buy a new shaft and install it as long as you agree to pay for it if that doesn't solve the problem. And that is exactly how that works.

 

[mrblaine]

The vibrations seem to be torsional, not radial. It had been proposed that DC shafts are less ideal due to the larger diameter chunk of mass in the H yoke and that maybe having two on the same vehicle and spinning them close to 4000rpm just isn't ideal. Maybe that's why Jeep never did it from the factory even though traditional logic would say the rear needed it as much or more than the front does due to the length.

I don't know what the answer is but I do know if it was simple and applicable across the board, we wouldn't have folks with hub kits and others that don't need them. The other point of data that should never be ignore is my 04 Unlimited had the cyclical vibe in bone stock condition once it got up to about 74 mph.

 

[Ashim]

Is it a correct assumption that this is not an issue for people running 35s with the 42RLE and 5.13 or higher gears due to the lower driveshaft speeds? that may be the ultimate solution if I can't manage to solve mine.

It is an incorrect assumption that the driveshaft speed is lower with the 42RLE. The drivehaft speed at a given road speed is the same regardless if the transmission is in drive or overdrive. The only difference is engine RPM.

 

[Rickyd]

It is an incorrect assumption that the driveshaft speed is lower with the 42RLE. The drivehaft speed at a given road speed is the same regardless if the transmission is in drive or overdrive. The only difference is engine RPM.

His not so clear assertion was that 35s vs his 33s would slow down the driveshafts for a given mph.

 

[Strizzo]

How much play is in the splined slip section? If you can wiggle it perpendicular to the shaft then yes,the driveshaft is worn out and you want a new one

I didn't notice any play in it when i was putting the transfer case back in, but i'll be under there again later this week or this weekend and i'll check it while I'm under there adjusting the pinion angle.

 

[Strizzo]

His not so clear assertion was that 35s vs his 33s would slow down the driveshafts for a given mph.

That is correct, it seems at least anecdotally that most of the topics chasing this issue are with 5.13 or higher ratios and 33s.

Doing a bit of math, a speedometer calculator spit out that with a 315/70-17 tire vs a 285/70-17 the 35 would be going 5.05% faster for a given rpm. If the engine is turning 2750 rpm at 75mph, then the driveshaft speed would be 3,985 rpm. going to the "35" would reduce engine speed to 2,617 rpm and driveshaft rpm to 3,793 rpm.

Maybe even more so if you ran a "true" 35x12.50-17. I say that because I just measured the "35" 315/70 on my bronco at 33" tall (after 30k miles) and the 285/70 on the jeep at 32" tall.

 

[Strizzo]

I don't know what the answer is but I do know if it was simple and applicable across the board, we wouldn't have folks with hub kits and others that don't need them. The other point of data that should never be ignore is my 04 Unlimited had the cyclical vibe in bone stock condition once it got up to about 74 mph.

fair enough that usually quiets down the wild claims, but this was just an "I replaced my driveshaft and it fixed my vibration" - guy wasn't claiming to have the solution to everyone's issues.

 

[mrblaine]

fair enough that usually quiets down the wild claims, but this was just an "I replaced my driveshaft and it fixed my vibration" - guy wasn't claiming to have the solution to everyone's issues.

By giving that answer in a thread about vibes, he actually was claiming to have a solution. Otherwise, you just be quiet and don't say anything.

 

[mrblaine]

That is correct, it seems at least anecdotally that most of the topics chasing this issue are with 5.13 or higher ratios and 33s.

Except for my bone stock 04.

 

[freedom_in_4low]

I would agree with you on spinning them 4000 rpms, but jeep did use two DC driveshafts on the rubicon models.

They did not. it was a bolt on instead of a slip yoke but it still only had 2 total u joints and no h yoke, therefore not a DC.

 

[freedom_in_4low]

I don't know what the answer is but I do know if it was simple and applicable across the board, we wouldn't have folks with hub kits and others that don't need them. The other point of data that should never be ignore is my 04 Unlimited had the cyclical vibe in bone stock condition once it got up to about 74 mph.

Yep, if this thread has accomplished anything it's making it clear that a simple fix hasn't been found.

I think we would agree that your 04 Unlimited is an outlier and for whatever reason has something special about it that makes it more sensitive to whatever is exciting these vibrations. And while there's not a hard-line threshold for driveshaft rpm where "x" is ok but "x+1" is bad, we do have enough to say that generally the exposure to this issue increases with increasing driveshaft rpm. It could very well be that EVERY TJ has this issue at some speed, but for many it's at a speed that is never explored.

I don't recall of a lot of examples outside your 04 that didn't have a DC shaft, either...but it's usually not practical to go back to a single cardan on most of these vehicles given their lift heights and tucks. An LJ might be able to get away with it but I'm not particularly motivated to buy another transfer case unless it's a significant upgrade. Guess I could try a single cardan with a slip shaft like the Rubi but set up for a SYEd 231 but has a decent chance of just trading oscillating vibes for real ones.

I still occasionally think about silly things like drilling a new mounting hole for the transfer case skid to make it match the early design (where the frame rails from rearmost skid bolt to the tank crossmember aren't the same length), since that's about the only common thing I haven't seen tried that would so heavily favor the later models. But since mine doesn't kick in until about 72 and I hate the wind and tire noise at that speed too much to spend much time at that speed anyway, I haven't had the drive to do anything more about it.

 

[Strizzo]

They did not. it was a bolt on instead of a slip yoke but it still only had 2 total u joints and no h yoke, therefore not a DC.

View attachment 603613

Ah, i hadn't looked very closely at them i guess i assumed it was a dc shaft stock. maybe that has something to do with it. the first time I read about the issue i wondered if the reason the vibration is cyclical is due to slightly different speeds front and rear (especially with Dana 30/Dana 44 having different size ring gears) combining and cancelling each other. I guess it could also have something to do with the fewer teeth on the pinion when you get down to that ratio.

it is probably a combination of a few different things stacking up, which is why there isn't a single, one size fits all solution.