Driveline vibrations are like a pack of woodchucks living under your barn. They're in your garden eating up the prize string bean patch, and excavating a terrorist cave network under your shop floor. The problem is obvious, yet all efforts to wipe them out only make it worse.
Does your driveline vibration problem feel like a pack of unwelcome woodchucks? Use this following guide to educate yourself and eliminate the vibration source.
The first step to solving the vibration issue is to identify the source. Spicer has a flowchart for troubleshooting vibrations, and it starts with gathering information and separating engine vibration from driveline vibration.
Performing simple tests and taking notes is helpful when troubleshooting the source of a vibration.
Gathering information is important when working with a project vehicle that has had major work before hitting the road.
The vibration follows engine RPM:
If the vibration follows engine rpm, then the problem is most likely related to an engine component out of balance. The source can include:
- Flywheel. There are neutral balance flywheels and external balance flywheels. Using the wrong one will shake the fillings out of your teeth.
- Rotating assembly (crankshaft, rods, pistons, damper). Some rotating assemblies are sold as "Balanced Rotating Assembly". We have witnessed countless customers assemble engines with "Balanced Rotating Assemblies", disassemble the engines, and then bring us the parts for a balance job.
- Coolant Pump. When the bushings let go in a coolant pump, that shaft and fan are thrashing around off the front of the engine, and it can be felt through the whole car.
The vibration is Speed dependent:
When the vibration is speed dependent, it is most likely related to the driveline. Note the frequency of the vibration. A low frequency that follows wheel speed inicates a problem with tires or axles. A balanced wheel and tire can still have broken cords and cause a vibration.
If the frequency of the vibration follows the speed of the driveline, the source may be:
Refer to the balance page for more information on how we high speed balance all driveshafts.
Driveline angles and vibration
The following video expains how U-Joint phasing causes vibrations:
For vibration free driveshaft operation, make sure your set-up follows these rules:
Driveshafts with 2 U-Joints:
UNIVERSAL JOINT OPERATING ANGLES ON EACH END OF A DRIVESHAFT SHOULD ALWAYS BE EQUAL WITHIN 1 DEGREE
OF EACH OTHER (ONE HALF DEGREE FOR MOTOR HOMES AND SHAFTS IN FRONT OF TRANSFER CASE OR AUXILIARY
The connecting driveshaft operates with an angle at each universal joint. It is that angle that creates a vibration.
A key point to remember about universal joint operating angles: To reduce the amount of vibration, the angles on each end of a driveshaft should always be SMALL.
To cancel an angle vibration, the universal joint operating angles need to be EQUAL within 1 degree at each end of a driveshaft. On motor home applications and auxiliary transmission installations, the tolerance is 1/2 degree.
Compound universal joint operating angles occur when the transmission and axle are not in line when viewed from BOTH the top and side. Their centerlines, however, are parallel in both views.
When a compound angle is present, the "True Universal Joint Operating Angle" of each universal joint must be calculated. It is the True Universal Joint Operating Angle that must meet the above rules.
The True Universal Joint Operating Angle, which must be calculated for each end of the shaft with compound angles, is a combination of the universal joint operating angle in the top view, as determined from the chart, and the measured universal joint operating angle in the side view.
Fix That Compound Angle
Compound universal joint operating angles are one of the most common causes of driveline vibration. To avoid theses problems, remember these important points:
• When setting up an application that requires compound universal joint operating angles, always keep the centerlines of the transmission and axle parallel in both views.
• Always keep the offset between their horizontal and vertical centerlines small.
What is an excessive operating angle?
The magnitude of a vibration created by a universal joint operating angle is proportional to the size of the universal joint operating angle. Spicer Engineers recommend true universal joint operating angles of 3 degrees or less.
Obtain the true universal joint operating angle, as explained above, and if it is greater than 3 degrees, compare it to this chart.
The angles shown on this chart are the maximum universal joint operating angles recommended by Spicer Engineers and are directly related to the speed of the driveshaft. Any universal joint operating angle greater than 3 degrees will lower universal joint life and may cause a vibration. Remember to check maximum safe driveshaft RPM by using the Spicer Safe Operating Speed Calculator.
What if the operating angle is too steep?
A double cardan constant velocity joint is exactly what it sounds like. The second U-Joint in the assembly cancels the vibration from the first so that the input and output shafts spin at the exact same velocity, independent of operating angle. Typical maximum operating angle for a CV joint is around 25 degrees. In some specialty applications, CV's are machined to operate at 34 degrees at highway speeds. This is only done in special cases.
Driveline set-up for the CV shaft is different than the standard 2 Joint shafts. In this case, the operating angle at the pinion must be less than 1.5 degrees. Most rigs will set the operating angle 1 degree low so that when the pinion tips up during acceleration, the operating angle does not become excessive.
Proper CV shaft set-up.
The most difficult part of installing a CV driveshaft, is getting the pinion angle right. This is a tedious process of shimming the leaf spring perches until the right angle is found. Once the proper pinion angle has been determined, the perches are cut from the axle tubes, and then welded back on in the right location. Click Here to see an example
Two Piece Shaft
In general, multiple shaft installations follow the same guidelines, except there are different recommendations for setting up the driveline:
• For a 2-shaft application, set up the first coupling shaft (sometimes called a jackshaft) so that the universal joint operating angle that occurs at the transmission end is 1 to 1-1/2 degrees.
• Try to avoid building a compound universal joint operating angle into the first coupling shaft by installing it in line with the transmission.
• If it ends up being compound, make sure the true universal joint operating angle, determined by using the information mentioned earlier, is 1 to 1-1/2 degrees. Install or tilt the axle so it is mounted on the same angle as the first coupling shaft (the centerlines of the axle and the first coupling shaft will be parallel).
Note: BY FOLLOWING THIS PROCEDURE, THE UNIVERSAL JOINT OPERATING ANGLE AT EACH END OF THE LAST SHAFT WILL AUTOMATICALLY BE EQUAL.
If there is an offset in the installation of the axle, make sure it does not create too large of a compound universal joint operating angle. Whenever possible, mount the axle directly in line with the first coupling shaft (when viewed from the top).