Chasing Front D/S Vibration Demons

JK_Dave

JK_Dave

Caught the Bug
I'll start with my current specs and then describe the problem I have.

Current specs:

'13 JKU lifted ~3.5"
Front Reel 1350 Double Cardan drive shaft
Front upper and lower control arms
Upgraded from 3.73 to 4.88 R&P gears
+4.4 deg caster on stock Rubicon D44 axle
2.5 deg angle measured from pinion yoke U joint when perpendicular to the ground
8 deg angle of driveshaft measured from the middle of the D/S body
Stock 32" tires

Double_Cardan_driveshaft.jpg

The problem:

Prior to my gear upgrade, all the specs above were the same and I had no vibration, even at highway speeds. Now, after the gear upgrade, I've got a mild vibration starting around 50mph and gets more noticeable at highway speeds. I have not had the D/S balanced because it's only been on the Jeep for 6 months and was brand new.

I called up Reel to get their thoughts and he agreed it sounded like I needed to adjust the angle, but couldn't tell me with any certainty how much. In fact, his suggestion was to talk to Mel or Drew since they install these all the time and seem to have success with them. Before I do that, I wanted to get some thoughts from others who are familiar with this.

My thought is that I need to attempt to straighten the angle between the shaft and the pinion yoke as much as possible, but I don't think I can add that much negative caster without encountering steering problems. Short of getting under there and adjusting the arms, test driving it and making further adjustments, can anyone give me their experience of a happy window I can shoot for? Does it sound like I'm taking the right approach here?
 
After not paying attention to the details I have removed my post to not confuse the issue.
 
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Edited to remove my reply with quote on branman's post per his request. (to keep the topic more clean)
 
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Rebalance the shaft. Fronts not under load and shouldn't vibrate with stockish caster numbers.
You can try running 3/3 but handling with suffer.
 
The reason I asked about the type of vibration is I focus on "what changed".

The OP stated they the vibration wasn't an issue until after a gear change. To me, this points to a possible poor gear set up. It is possible that the mesh it too tight and causing vibration that resonates though the DS or perhaps something is loose.

Gear vibes are usually more constistant. while DS vibs usually resonate with variation. "whir-whir-whir". I know this isn't always the case but it's what I've seen. There are a buch of guys doing gear swaps out there that have no idea what they are doing!
 
Lower gearing = higher RPMS. If the shafts going to vibrate. It's going to happen with deeper gears. I see it a lot with folks running higher lifts, a double carden shaft and stock housing. Huge benefit with a Prorock is added caster/pinion angles.
 
2007blackJk said:
Lower gearing = higher RPMS. If the shafts going to vibrate. It's going to happen with deeper gears. I see it a lot with folks running higher lifts, a double carden shaft and stock housing. Huge benefit with a Prorock is added caster/pinion angles.
Click to expand...

Good point! :thumb:
 
jnabird333 said:
The reason I asked about the type of vibration is I focus on "what changed".

The OP stated they the vibration wasn't an issue until after a gear change. To me, this points to a possible poor gear set up. It is possible that the mesh it too tight and causing vibration that resonates though the DS or perhaps something is loose.

Gear vibes are usually more constistant. while DS vibs usually resonate with variation. "whir-whir-whir". I know this isn't always the case but it's what I've seen. There are a buch of guys doing gear swaps out there that have no idea what they are doing!
Click to expand...

I do agree. Of coarse it's possible.
 
I have the same problem, between 55-65mph get a vibration which feels like it could be the rear driveshaft. It was fine until I regeared. I'm running stock rear ds and tom woods front. I took it back and had them recheck the gears. They said everything is right. Took it back again and had rear ds rotated 180, still vibrates. I'm at a loss.

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JK_Dave said:
I'll start with my current specs and then describe the problem I have.

Current specs:

'13 JKU lifted ~3.5"
Front Reel 1350 Double Cardan drive shaft
Front upper and lower control arms
Upgraded from 3.73 to 4.88 R&P gears
+4.4 deg caster on stock Rubicon D44 axle
2.5 deg angle measured from pinion yoke U joint when perpendicular to the ground
8 deg angle of driveshaft measured from the middle of the D/S body
Stock 32" tires

View attachment 113022

The problem:

Prior to my gear upgrade, all the specs above were the same and I had no vibration, even at highway speeds. Now, after the gear upgrade, I've got a mild vibration starting around 50mph and gets more noticeable at highway speeds. I have not had the D/S balanced because it's only been on the Jeep for 6 months and was brand new.

I called up Reel to get their thoughts and he agreed it sounded like I needed to adjust the angle, but couldn't tell me with any certainty how much. In fact, his suggestion was to talk to Mel or Drew since they install these all the time and seem to have success with them. Before I do that, I wanted to get some thoughts from others who are familiar with this.

My thought is that I need to attempt to straighten the angle between the shaft and the pinion yoke as much as possible, but I don't think I can add that much negative caster without encountering steering problems. Short of getting under there and adjusting the arms, test driving it and making further adjustments, can anyone give me their experience of a happy window I can shoot for? Does it sound like I'm taking the right approach here?
Click to expand...

The diagram you have posted is intended for the rear shaft ONLY. When it comes to your front shaft, you have to account for caster and so you cannot set your pinion angle in line with your drive shaft. If you really are at +4.4°, you really need to try and get it closer to +4°. That should help.
 
jnabird333 said:
Is the vibration constant or more of a whir-whir-whir?
Click to expand...

I would say it's pretty constant. You can feel it through the floor and pedal pretty easily.

jnabird333 said:
The reason I asked about the type of vibration is I focus on "what changed".

The OP stated they the vibration wasn't an issue until after a gear change. To me, this points to a possible poor gear set up. It is possible that the mesh it too tight and causing vibration that resonates though the DS or perhaps something is loose.

Gear vibes are usually more constistant. while DS vibs usually resonate with variation. "whir-whir-whir". I know this isn't always the case but it's what I've seen. There are a buch of guys doing gear swaps out there that have no idea what they are doing!
Click to expand...

This is possible. I had 4WP do the gears for me because that's above my limit. I'm pretty limited in my area in terms of expertise, but I can always take it down to East Coast Gear Supply and have them recheck the tolerances for me just to get a second opinion.

2007blackJk said:
Lower gearing = higher RPMS. If the shafts going to vibrate. It's going to happen with deeper gears. I see it a lot with folks running higher lifts, a double carden shaft and stock housing. Huge benefit with a Prorock is added caster/pinion angles.
Click to expand...

You hit the nail on the head. I do expect some vibration from adjusting so many things away from stock settings. But I really don't feel comfortable driving over 65 on the highway for fear of causing damage to either my transfer case bearings or my differential bearings. Neither of those will be cheap to repair. A Prorock would be great, and may be in the cards someday, but not now. If I could get those extra 6 degrees without affecting my caster then I could call it a day.

wayoflife said:
The diagram you have posted is intended for the rear shaft ONLY. When it comes to your front shaft, you have to account for caster and so you cannot set your pinion angle in line with your drive shaft. If you really are at +4.4°, you really need to try and get it closer to +4°. That should help.
Click to expand...

Yes, I agree it's for the rear shaft. I really haven't found much in terms of the front. I just wanted to see if the same theory could apply to the front, but it sounds like I may be trying to go too far if I dial in 2-3 deg of negative caster. I'll try to target just .5-1 deg initially and then take a test drive. Right now the steering feels great, so hopefully I have some wiggle room there.
 
JEEP FAM said:
I have the same problem, between 55-65mph get a vibration which feels like it could be the rear driveshaft. It was fine until I regeared. I'm running stock rear ds and tom woods front. I took it back and had them recheck the gears. They said everything is right. Took it back again and had rear ds rotated 180, still vibrates. I'm at a loss.

Sent from my XT1030 using WAYALIFE mobile app
Click to expand...

Your profile says you have a four door, but doesn't say how much lift you have. If you think the problem is in your rear and you're running a stock shaft back there, you may just need to adjust the pinion angle of your rear axle to be more in line with the D/S angle. Maybe you're maxing out the angle the stock CV joints can flex to? If you have adjustable arms, you should be able to adjust this fairly easily. Also, confirm there's no visible signs of damage to the shaft as well.
 
Just to confirm, are you saying that the vibration you have is "constant" as in, a solid buzzing? Because, that's typically something you would feel with a rear shaft that's not aligned with your pinion but, I see you are still running a factory shaft and that shouldn't happen regardless of what angle it's in. Also, if the vibrations were coming from your front shaft, the vibrations should oscillate in a sine wave. In other words, it'll always be there but it would come and go and come and go in intensity. Of course, if you're not sure, you can always remove your front shaft and drive around without it. That will help you to know for sure.

As far as caster adjustment goes, a degree change can go a long way.
 
JEEP FAM said:
I have the same problem, between 55-65mph get a vibration which feels like it could be the rear driveshaft. It was fine until I regeared. I'm running stock rear ds and tom woods front. I took it back and had them recheck the gears. They said everything is right. Took it back again and had rear ds rotated 180, still vibrates. I'm at a loss.

Sent from my XT1030 using WAYALIFE mobile app
Click to expand...

I hate to break the news to you but your problem is most likely your Tom Woods shaft. It's probably just out of balance and the new gears are just making them noticeable being that it now spins so much faster. Of course, all you need to do is remove it to know for sure.
 
The front shaft on my 4-door vibrates with oscillation just a little bit between 50-60 MPH. It is not very noticeable but I know it is there. I don't want to remove any more caster so I'm just living with it and checking the joints often. (Hopefully this will not get too much worse with my upcoming gear change.)

The 2-door I recently purchased my wife had a constant vibration, which I originally thought was being caused by the rear shaft not being aligned properly. Once I corrected it there was only a moderate change. Then, while correcting some other suspension issues I found a BUNCH of play in the pinion of the front. Once the diff was rebuilt the constant vibration was gone. I still have a touch of oscillating vibration, but like my 4-door do not want to remove any more caster. Unfortunately, this Jeep has Tom Wood's shafts with the cheap joints. I think one of them may be going and the shafts need rebalancing.... I want to correct this before addressing any more caster.

I have read several struggle to remove all front vibrations with a 1350 jointed shaft in the front. I'm curious what everyone's experience with this has been...
 
I think I will start with the removal of the front drive shaft and see what happens.

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