Droning and vibration

[TurboTJ]

I have a 2006 TJR with a 2 inch Currie/OME lift, a Tom Woods DC drive shaft and a Barnes skid plate that raises the TC about 1 inch. For a long time I have had droning from about 50 to 60 MPH. It was not particularly bad but noticeable. My pinion angle was a little too low (one to two degrees) so I decided to adjust the control arms to bring it up a bit. At first glance, it was a good thing to do because it eliminated the shudder I could get when engaging the clutch in first or reverse. But then I took it for a drive and the drone was much worse, bad enough that I can feel it now. It comes and goes on about a 3 second basis. So this is a dilemma. Bringing up the pinion eliminated the shudder when engaging the clutch, but made the drone much worse. Huhhh? The driveshaft was recently re-balanced so I don't think that is the problem. It seems like I am going to have to lower the pinion again and just live with some droning and some clutch engagement shudder. Got any other ideas?

 

[DrDmoney]

You could pull the rear DS to isolate the problem and confirm it’s the pinion angle/DS.

 

[TurboTJ]

You could pull the rear DS to isolate the problem and confirm it’s the pinion angle/DS.

Yeah, I will do that but don't you think that when changing the pinion angle made the drone worse that it has to be the rear drive shaft? BTW, I measured the frequencies of the droning with a vibration analyzer and it matched the shaft rotation speed and also half the rotation speed.

 

[DrDmoney]

Some TJ’s for whatever reason are sensitive to pinion angle changes taking the DS out eliminates the DS and the pinion angle. If the vibes go away then you can start playing with the DS/pinion relationship.

 

[DrDmoney]

Yeah, I will do that but don't you think that when changing the pinion angle made the drone worse that it has to be the rear drive shaft? BTW, I measured the frequencies of the droning with a vibration analyzer and it matched the shaft rotation speed and also half the rotation speed.

The frequency thing is interesting, does acceleration, deceleration, or coasting change the vibe? What gear ratio are you running? Lockers, LSD, or open diff?

 

[AndyG]

Some TJ’s for whatever reason are sensitive to pinion angle changes taking the DS out eliminates the DS and the pinion angle. If the vibes go away then you can start playing with the DS/pinion relationship.

Agreed and you want the pinion a skosh low to compensate for torque lift.

Why it solves the shudder and makes the drone worse I don’t know, and a CV drive shaft and less angle may be the ticket with your TJ ...it was with mine and I went a long time with no issues til I made a slight adjustment.

I know in theory you shouldn’t have to go that route, but my 4 year old should not have taken a sweater fuzz shaver to his weiner either. Things you can’t explain happen.

Talk about hearing a noise. Boy Howdy.

 

[TurboTJ]

The frequency thing is interesting, does acceleration, deceleration, or coasting change the vibe? What gear ratio are you running? Lockers, LSD, or open diff?

Answers to your questions:

1) Acceleration, deceleration, coasting, in-gear, out-of-gear, clutch in, clutch out make no difference.
2) Standard Rubicon 4.10 gears.
3) Standard Rubicon gear-type LSD with pneumatic locker in the rear, pneumatic locker in the front.
4) The rear drive shaft is a Tom Woods with a double-cardan joint.

The drone comes on right around 50 MPH and goes away slightly above 60 MPH. It is perfectly quiet and smooth at 45 and 65 MPH. The rear pinion is currently about 1 degree below the drive shaft. It was about 2 degrees before. I love how smooth the clutch engages now but the drone is really pretty bad now.

 

[TurboTJ]

Latest datapoint... I removed the rear drive shaft and the drone is almost totally gone, but there is still a hint of it. I will remove the front drive shaft next.

 

[DrDmoney]

Latest datapoint... I removed the rear drive shaft and the drone is almost totally gone, but there is still a hint of it. I will remove the front drive shaft next.

My first guess is pinion bearing. Did it still happen at the same speed?

 

[TurboTJ]

My first guess is pinion bearing. Did it still happen at the same speed?

Yes, between 50 and 60 mph. I can detect no play in the pinion bearing

 

[TurboTJ]

Latest data: I disconnected the front drive shaft and the droning disappeared. Ok, so it almost disappears with the rear disconnected and totally disappears with the front disconnected. That and the fact that bringing the rear pinion up to within one degree of the drive shaft made the droning much worse is sort of confusing, but I am most suspicious of the front drive shaft. I put a hose clamp on that shaft as close to the DC as possible and tried four different positions 90 degrees to each other. I found one position that I think reduces the droning somewhat. So my next move is to get that shaft re-balanced. Standby for more.

 

[Rubicon88]

U-joints are far too often over looked.
A lot of folk think no way it can be my u-joints. Why? Well they yank and poke and prod and think yep.. all good. We change many u-joints that customers swear are fine only to show them (to their surprise) the issue is now gone.

I'm not saying yours is u-joint issues but when was the last time you changed them and what type did you use.

 

[DrDmoney]

Latest data: I disconnected the front drive shaft and the droning disappeared. Ok, so it almost disappears with the rear disconnected and totally disappears with the front disconnected. That and the fact that bringing the rear pinion up to within one degree of the drive shaft made the droning much worse is sort of confusing, but I am most suspicious of the front drive shaft. I put a hose clamp on that shaft as close to the DC as possible and tried four different positions 90 degrees to each other. I found one position that I think reduces the droning somewhat. So my next move is to get that shaft re-balanced. Standby for more.

It’s odd that a pinion angle adjustment made it worse, especially one that made the PA better, could be harmonic both shafts rotate at the same rpm.

 

[williambmac]

so you raised the transfer case 1" and have a 2" suspension lift.

your drone basically disappears when you remover the front drive shaft?

Have you checked the front d/s angle and adjusted the pinion angle at all?

I realise that the skid only bumps the tranfer case up an inch but have you considered a motor mount lift to level things out?

One thing you can try and do, go get yourself some 1/2 flat washers and use them to systematically drop the skid plate down in increments of a 1/4 inch (1/4, 1/2, 3/4) and see if the drone goes away.

 

[TurboTJ]

U-joints are far too often over looked.
A lot of folk think no way it can be my u-joints. Why? Well they yank and poke and prod and think yep.. all good. We change many u-joints that customers swear are fine only to show them (to their surprise) the issue is now gone.

I'm not saying yours is u-joint issues but when was the last time you changed them and what type did you use.

I replaced all of the front shaft spiders and the DC centering ball about two years ago using Spicer parts. I did not have the front shaft re-balanced at that time. The rear shaft was just re-built and re-balanced by Tom Woods about six months ago.

 

[TurboTJ]

so you raised the transfer case 1" and have a 2" suspension lift.

your drone basically disappears when you remover the front drive shaft?

Have you checked the front d/s angle and adjusted the pinion angle at all?

The front drive shaft angle looks right to me. The pinion is just slightly higher than the drive shaft. It is displaced to the left about half an inch because I do not have an adjustable track bar. I really couldn’t move it right any more because the U-joint knuckles have already hit and dented the exhaust runners. I didn’t have that problem until a new exhaust system was put on a few years back.

 

[Rubicon88]

I replaced all of the front shaft spiders and the DC centering ball about two years ago using Spicer parts. I did not have the front shaft re-balanced at that time. The rear shaft was just re-built and re-balanced by Tom Woods about six months ago.

Ok...you are or are not using new u-joints in the rear and front?

 

[TurboTJ]

The front driveshaft U-joints were new two years ago. The rear driveshaft u-joints were new about three years ago although the centering ball was replaced by Tom Woods about six months ago (the seal had torn). The axle u-joints have never been replaced. The droning frequency corresponds to the drive shaft rpm.

 

[freedom_in_4low]

I wouldn't read too much into what the pinion angle actually is, I'm dealing with a similar issue and from talking to some very experienced folks around here, it seems pinion angle is a lot like control arm length - in that the actual measurement is whatever it needs to be to achieve the desired results, which for control arm angle is a properly located axle, and for pinion angle is vibration-free operation. @mrblaine specifically cited examples he's had where the final pinion angle defied all conventional wisdom about what should be considered driveable, like 5° off.

Generally though, the guidance is to pull the front shaft, set the rear to eliminate vibrations as best as possible, then put the front back in and start tuning it until the vibes are gone. Since you pulled the front already and the droning was gone, then the rear is likely ok and the issue is with the front. That is assuming the vibration is gone entirely - if it's still vibrating, but has become constant instead of the in-and-out pulsation, that just means that the front isn't there to stack on top of the rear but the rear still needs some work.

In my experience, a driveline angle has to be WAY out of whack to cause shudder at takeoff. I can't explain why that changed with a small change to an angle that wasn't far off to begin with.