BroncoII4x4.com

I own an 89 2WD BII that will one day become a 4WD BII, but for the moment I have to fix what I got. The reason I mention the fact that it is a 2WD is because all BII's of this type had the dummy Xfer case and I am trying to find the cause of an annoying driveline vibration and no longer sure what the cause could be.

I eliminated the stock driveshaft (the cause of the 65 to 75 MPH vibration) and bought a u-joint style telescoping one similar to what is available at Duff Enterprises with the only difference being that it does not have the double u-joint at the transmission end (see link: http://www.jamesduff.com/broncoII/drivetrain.html Now the vibration is constant and it shows up at about 45 MPH and does not go away.
Could the driveshaft be binding up? or not balanced (unlikly)?

If anyone has an idea what the issue is or how to troubleshoot this I would greatly appreciate the info.

First, make sure the yolks are in phase. Meaning, the slip yolk should be lined up with the yolk at the other end.

Second, the purpose of the double u-joint (double cardan) is to elimate vibration, allow more extreme operating angles, and allow different angles at the transfer and axle.

Without a double cardan joint, the angles at the transfer case and rear axle need to be the same. This is a problem, becuase the pinion on a BII is offset, hence the factory double cardan or CV.

If I was handed the driveshaft new in box there is the assumption that the slip yolk would be lined up with the yolk at the other end. I'll check this.

ok nooby comment to follow. The new driveshaft has u-joints at both ends so I am not sure how much different it could be from the factory design. Does the CV style driveshaft perform differently?

Well, you said you only have ONE joint at the tranfer case. So yes the Dual joint(double cardan) constant velocity joint will elimate vibrations mentioned above.

Awesome! thanks for the info.

if that checks out, have the balance of your rear tires chacked. they will cause a vibration at certain speeds and not others also.

Check the rims for mud and other gook stuck to them

a broken belt inside of a radial will also cause vibrations at certain speeds.

a broken belt is very bad! if you put the rear up off the ground you should be able to spin the wheels one at a time and feel a "lump" in the tire when you spin it or run your hand around the tire. it is what we call "out of round". I have seen many bad tires but broken belts are scarry!

DBrown wrote:a broken belt is very bad! if you put the rear up off the ground you should be able to spin the wheels one at a time and feel a "lump" in the tire when you spin it or run your hand around the tire. it is what we call "out of round". I have seen many bad tires but broken belts are scarry!

yes they are, especially at those speeds. I had a similar problem on a ranger and the tire place did a computer balance and did not find this. After not being able to figure out the vibration problem, I took it to a mechanic. He did the simple thing that DBrown mentioned and it turned out to be one tire with a broken belt.

yeah, the balancer will just tell you what weight you need to put where to make it happy. I had a friend drive an hour to my house to look at his suspension because of vibration......he had a bused belt that by the time he got here you didn't even have to put it off the goundto see it. the tire was showing the steel belts from where the rubber was split on the sholder of the tire. needless I got him a hook up on some tires from work.

The final word.

First, I checked the slip yolks and they were in phase.
I then took the drive shaft back to the shop to check it out. It was off by .4000 of an inch. Not really enough to complain about. Anyway, when I got it home, I reinstalled the shaft but this time I put the telescoping end at the transmission side and the single joint on the differential side. I torqued it and went for a drive. It drives like butter. No vibration, nada. Go figure!