New thoughts about the drive shaft vibration issue...please read

[1990Coupe]

Found this thread via search. I thought i was the only one who had a vibration issue!! I finished my project, and i have a vibration at highway speeds. You can "hear" it at about 65mph and it gets worse and louder anything over that. My U joints looked good, and The car is lowered. I have new uppers and lowers but they are non adjustable.

The DS is from the junkyard, i have no idea what year it was from. I kinda just found it on the ground at the salvage yard and took it There are another set of holes on the pinion gear i wonder if i switch to those holes that will make a difference? I kinda don't know what to do haha. i build this car to be my cruiser so it will be on the highway alot.

 

[93 LX]

you may want to clock (rotate) the pinion end 90 degrees at a time until the vibration is gone.

 

[1990Coupe]

I honestly have no idea how do to that!

 

[phutch11]

I had the same problem in my 66 - which clearly has leafs and thus some different issues, but the basics of the solution are the same.

The key is not just the pinon angle, but also the angle of the driveshaft at the pinon u-joint, the driveshaft angle at the tranny and the angle of the tranny.

What you want is for these corresponding angles to be as close to the same as possible. So if your tranny slopes down at 2 degrees (front to rear), you want your pinon to be angled up 2 degrees (back to front). This will put the drive shaft angles (at tranny and pinion) at equal and you will have zero vibrations. That assumes you've got no other issues.

You will want this equal state to occur while the drivetrain is under load, thus you'll probably want to factor in a few degrees rise into the pinon angle. That means if you tranny slopes at two degrees down you'd set your pinon angle to zero to allow it to rise under load. You'll have to play with this to get it exactly right.

If you have swapped in a different third member you need to consider the side to side angluarity in the pinon is now in a different location than the original.

Good luck...




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[1990Coupe]

1) I have non adjustable upper and lower control arms. Therefore playing with pinion angles is not possible

2) here is where I don't understand the pinion angle thing. Lets say you have the tranny down 2 degrees and pinion angle up 2 degrees thus creating almost a straight shot with the driveshaft, whats the purpose of the U joint then? i have seen plenty of trucks and cars where they did not have the same angles and the driveshaft was allowing the u joints to do their job, and allowing suspension movement, and they do not vibrate??


I know that probably doesnt make any sense but i don't know how to word it

 

[phutch11]

The angles don't have to be a straight shot altought that would be ideal. What you want is the same angle.

So say that the tranny angle is zero and so is the pinion but that the pinion is six inches lower - clearly the u-joints are doing their job but you'll have no vibrations as the angles are the same.

What you don't want is a two degree slope on the tranny and a two degree down slope (rear to front) on the pinion. Visualize that and it should help to make sense.

Additionally there is an upper limit of the angle that a u-joint can take and still live a long life...I think like 6 degrees.

Posted via Mobile Device

 

[1990Coupe]

The angles don't have to be a straight shot altought that would be ideal. What you want is the same angle.

So say that the tranny angle is zero and so is the pinion but that the pinion is six inches lower - clearly the u-joints are doing their job but you'll have no vibrations as the angles are the same.

What you don't want is a two degree slope on the tranny and a two degree down slope (rear to front) on the pinion. Visualize that and it should help to make sense.

Additionally there is an upper limit of the angle that a u-joint can take and still live a long life...I think like 6 degrees.

Posted via Mobile Device

Ok that makes more sense i understand... Thanks!!



I'm going to probably unbolt the driveshaft and turn it to the other set of bolt holes and see if that makes a difference. Otherwise i'm at a loss?