Harmonic vibration above 70MPH

[big66440]

My Comanche has a vibration that begins at 70 MPH, it's not an " wheel out of balance"  shake but more of a pronounced humming you can feel on the floor board and hear through the cab. I have replaced the extension housing bushing in the transmission,u-joints, spider gears and rear wheel bearings which where worn out anyway. I know these problems are difficult to diagnose without audio/visual but have any of you had a similar problem? I'm leaning towards the drive shaft having to do something with it since It's got that stupid rubber insert, any of you guys have a clue to what may be causing it? thanks

[Marine1Texas]

how are your front wheel hub assembles? are the bearings good with good lube.

I can think of all kind of places that could make noise. Even a slight warped rotor that is just grazing the brake pad can make weird noise.

[big66440]

Front bearings are well packed with Mobil 1 bearing grease and adjusted to factory shop manual specs ( 2WD ), Brake pedal is very solid and shows no signs of warped parts.

[big66440]

Bump?

[64 Cheyenne]

Suggest having the DS balanced, or poor man balance with two hose clamps on the DS.

Put them both at 12 oclock, drive, if bad or worse move clamps till better at both 180*, then split at 270* etc.

Without being there myself I wouldn't totally rule out a tire issue either, could have thrown a wheel weight and or something causing an out of balance like mud or debris in wheels or brake drums?

[big66440]

SOLVED- It was the driveshaft, I guess the rubber inside was failing and the fact that these shafts weight a ton was not helping. I got a brand new driveshaft made and its smooth as glass now.

[TheDude]

Do you mean the front driveshaft?

 

 

1989 Jeep Comanche 4.0L 5 Speed 4x4 Long Bed 4.10s LSD

1991 Jeep Comanche 2.5L 5 speed Red Short Bed

[HOrnbrod]

The OP has 2WD.

[TheDude]

Oh, OK. I didn't realize there was any rubber components in the rear driveshaft.

 

 

1989 Jeep Comanche 4.0L 5 Speed 4x4 Long Bed 4.10s LSD

1991 Jeep Comanche 2.5L 5 speed Red Short Bed

[64 Cheyenne]

Oh, OK. I didn't realize there was any rubber components in the rear driveshaft.

 

 

1989 Jeep Comanche 4.0L 5 Speed 4x4 Long Bed 4.10s LSD

1991 Jeep Comanche 2.5L 5 speed Red Short Bed

 

FYI, some people assume that because the (stock) MJ DS is internally dampened with a huge chunk of rubber it cannot be shortened,

it can be shortened, and will work, mine was shortened, and works well.

[HOrnbrod]

FYI, some people assume that because the (stock) MJ DS is internally dampened with a huge chunk of rubber it cannot be shortened,

it can be shortened, and will work, mine was shortened, and works well.

Of course the 2WD shafts can all be shortened. The problem is that sometimes they can't be balanced afterwards because of the deteriorated rubber sheath inside.

[big66440]

 

FYI, some people assume that because the (stock) MJ DS is internally dampened with a huge chunk of rubber it cannot be shortened,

it can be shortened, and will work, mine was shortened, and works well.

Of course the 2WD shafts can all be shortened. The problem is that sometimes they can't be balanced afterwards because of the deteriorated rubber sheath inside.

 

Thanks Hornbrod, that was the case with mine.

[HOrnbrod]

Mine too.   :thumbsup: