Chasing Driveline Vibes

[dz1087]

Well, I haven't checked the new angles, but I think the vibes are worse now with the 8* of shims under the spring. If they are not worse, and it is just in my head then there definitely wasn't any improvement whatsoever. I'm going to have it aligned tomorrow, so I'll talk with the guys there and see what they think.

 

[xxxjjj]

Had the same issue, at approximately 30 mph. Shims and a replacement of the rear driveshaft eliminated this problem.
My conclusion is that the driveshaft was out of balance.
Hope this helps

spec: 89, 2dr, 5.5'', no sye

 

[dz1087]

Well, damn. I hope that isn't it. I just had the driveshaft rebuilt/rebalanced less than a year ago.

Since I'm about 17* of depression from the tcase, could I just be reaching the upper limits of the CV joint?

 

[xjbubba]

Well, I've read 15* shaft inclination is about max, and that you should expect "some" vibration at the point. A chart showing max drive line angles (for theoretical optimal life) indicates ~6* operating angle for a shaft rotation of ~2750 RPM, and 5* operating angle for ~3500 RPM. Calculate your shaft RPM at 60 MPH by dividing 20168 by tire OD, then multiplying that by your differential ratio. For me it's 20168/33 x 4.56=2787 shaft RPM at 60 MPH; multiply that by 1.25=3484 RPM at 75 MPH. The table shows the obvious correlation between theoretical max u-joint operating angle and shaft RPM; the higher of either results in lower life (and implies potential for vibration).