Driveline vibration

[OnorOffroad]

I recently installed a 9" in the rear, no shims. I have an SYE and a double cardan DS. At about 45mph under load there is a slight but noticeable vibration and increased humming noise. The vibration only occurs under load, and seems to stop at about 55 or 60.

My guess is that I need to shim the axle to correct the pinion angle, but when I took the measurements it was only 1-2deg different between the DS and the pinion. Would that be enough to make it vibrate like that or should I be looking at something else?

Thanks.

 

[Devilfrog]

what's the condition of the 3 u-joints?
what's the condition of the slip shaft?
what's the condition of the centering yoke?
Can you post a side picture of your pinion angle?
Is there any noticeable damage to the shaft?
how's the balance on your tires?
Generally a driveshaft vibration issue would occur fromt the point it started spinning. Tire issues tend to be more of a speed dependant nature.

 

[OnorOffroad]

Everything up to the axle is in good condition, I wasn't having any vibes/noise with the 8.25".The U-joint at the pinion is new, the other two look good to me. The shaft should be good too, as nothing has changed since the install. The centering yoke has one of the U-joint retaining pieces tore off. The tires didn't vibrate and were not out of balance before the install.





http://imageshack.us/photo/my-images/812/img20120703095140.jpg/

 

[OnorOffroad]

 

[X E Ryder]

The pinion looks too high to me in that last pic, and it would only go higher under load. It looks +1 or 2 and should ideally be -1 or zero at highest, yea?

Still, its such a small amount of error I'm surprised you have vibration unless you drive very fast.

 

[OnorOffroad]

The pinion is inline with the DS though. Vibration occurs somewhere in the 40's to 50's, seems to drop off after that, and when I let off the gas there are no vibes.

 

[blubullett]

Your pinion looks too high. You said that it is only 1-2 degrees off in your fisrt post. Was that 1-2 degrees too high? Your pinion should be pointing slightly under the driveshaft.

 

[OnorOffroad]

I only measured the DS angle and then the pinion angle and noted the difference. I didn't write down the angles for each. I'll measure again tomorrow. SO if it's 1-2 deg too high, then I need to get something like a 3deg shim to get it slightly below?

 

[X E Ryder]

Your pinion looks too high. You said that it is only 1-2 degrees off in your fisrt post. Was that 1-2 degrees too high? Your pinion should be pointing slightly under the driveshaft.

Yea that is exactly what I'm seeing too. When you torque the axle, especially in 4L that thing is going to go too far Positive.

Shoot for 0 or -1 at least on a CV rear shaft is the rule of thumb.

 

[OnorOffroad]

The DS was 14, and the pinion was 16-17 (harder to measure). So I'm thinking a 3deg shim should do the trick. Thanks for the help.