Technical Notes about Repairs and Rebuilds in Lorton, Virginia

 

DriveLine 101

Introduction:

Have you noticed a vibration or rumbling noise when you are driving down the highway? If you have a lot of miles on your vehicle, have you modified the suspension or drive train in any way, you may be experiencing driveline vibration.

Ideally you want the two ends of a double-U-Joint drive shaft within a few degrees of each other for maximum u-joint life and minimum vibration. This is actually the operating angle (under load) and not the angle of the drive shaft to the u-joints themselves (that has its own limit).
Since the rear pinion moves up under acceleration (unless you have anti-wrap control on the axle) ideally you set up the static pinion angle to be 1-2° below the transfer case output flange angle. This way, as the pinion twists up, it comes into a good alignment with the transfer case.
In my case, I stuck on a 1.5" longer shackle and from some simple trig, came up with needing about a 3° shim to compensate for the extra tilt of the shackle. I never measured the angles at the time. Later, I did measure and found even with 3°, I was still 1° above the transfer case and I needed to add another 2-3° to get me passed zero and into the desired range. So I have to conclude that originally my pinion angle was off with the stock shackle as well. Driving experience also confirmed this, I had drive line vibration under load (pinion tips up), but it would go away under coasting conditions (pinion tips down).
 
Machine Gears — Transmission Builds in Lorton, VA
 
So my point is to measure what you have now and see if its OK and how much will it change with a longer shackle.
 
Shaft Vibration — Transmission Builds in Lorton, VA
 
Joint & Shaft Measurements — Transmission Builds in Lorton, VA
 
High Shaft Quality Equipment — Transmission Builds in Lorton, VA
 

Shaft Vibration

Vibration in driveline assemblies can be caused by many things. Worn parts, damaged assemblies, poor quality components and un-balanced assemblies are some of the leading causes of shaft vibrations. Great care must be provided in order to keep the rotating assembly operating smoothly and trouble free.

Balancing:

Any drive shaft operating and RPM levels above 500RPM should be balanced to that rpm level. Even the straightest shaft in the business will be out of balance if the distribution of mass is unequal. The rough castings that most components are made of rarely have an equal distribution of mass. More importantly, a basic law of physics spells trouble for unbalanced shafts. Imbalance forces increase at the square of the RPM. This means that when the RPM is doubled, there is a 4 fold increase in force. Triple the RPM and see a 9 fold increase in force. Quadruple the RPM-16 fold increase. That's why vibrations typically get worse with an increase in speed. Say for instance a drive shaft is balanced at 1000 RPM, but wasn't balanced very closely, or worse yet, wasn't held properly in the machine due to worn or mis-aligned machined tooling. If that shaft operates at 3000 RPM in the vehicle, the residual imbalance will produce forces 9 times greater than at the 1000 RPM balance speed. It is best to balance a shaft at actual RPM speeds.

Lubrication:

Worn parts are a common cause of vibration in rotating assemblies. Failure maintain proper lubrication of rotating joints will cause shaft vibration as well as shaft failure. Great care must be taken to ensure the rotating assembly is properly lubricated for years or trouble free use.

Damaged Assemblies:

Damaged assemblies can cause tremendous vibrations in rotating assemblies. Damaged rotating assemblies should be repair or replaced at once to ensure the assembly does not fail and possibly causing failure to surrounding components or machinery.

Component Quality:

Poor quality parts have been know to cause vibration in rotating assemblies due to specification variances in the different manufactured parts. Poor quality parts will have a greater tendency to cause vibration as well as assembly failure. Only quality parts should be used in any rotating assembly.

U-Joint & Shaft Measurements

Measuring Drive Shaft and U-Joints

  • If you decide to jack up your vehicle it will change the dimensions, and your vehicle needs to be measured as is in order to operate.
  • Between U-Joint centerlines, measure if you have a bolt-on transmission yoke for your vehicle.
  • If there is a flange mount on either or both ends, measure to the faces.
  • When you install U-bolts do not over-tighten them. "D" dimensions 1-1/16" and 1-1/8": 14 to 17 ft. lb.; "D" dimension 1-3/16": 10-25 ft. lb.; "D" dimension 1-3/8": 32-37 ft. lb.
  • If you have specified grease able U-joints, grease them after installation of drive shaft.

Measuring For Two-Piece System

  • Measure from the tip of the transmission output shaft to the centerline of U-joint at the third member. This will be the flat surface where the U-bolt hole is drilled. Take note of this measurement for use on the form as transmission output shaft to U-joint centerline.
  • Measure the output shaft protrusion and take note of this measurement.
  • In addition to these measurements, you will need to identify the transmission make and model and the differential make and model.
 

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