In recent years, the driveshaft and its applications have undergone some significant changes. Until that time, the basic driveshaft had remained largely unchanged in design and function for decades. Although still the "fusible link" between transmission and differential as its predecessors were, the vehicle around the shaft has evolved exponentially. This includes everything from passenger cars right up to Big Rigs on and off the highway.

Probably the biggest factor in the rash of driveline vibration complaints is due to the fact that nearly all vehicles have been reduced in weight. Shear mass used to absorb many drivetrain vibrations. That mass is simply no longer there. It was removed to provide for a more fuel efficient vehicle. Couple that with the strides in general automotive technology along with better tires, suspensions, quieter gearing, higher RPM engines, overdrive transmissions and you have a formula for drivetrain vibrations.

Remember, during this technological redo of the vehicle from the ground up, the poor little driveshaft remained basically the same. In addition to that, efforts to curb manufacturing costs on aftermarket driveline components led to an increase in many clearances in these parts.

Is it any wonder why shops in the driveline repair business are seeing an increase in customer vibration complaints on old and brand NEW vehicles alike? For those armed with the right tools and knowledge, this can be met as welcome challenge. First, the driveline shop must understand that, as Bob Dylan once said,"the times,they are changin". When it comes to driveline repair, you simply cannot get away with the things you used to. When fabricating a shaft, all the components used in the vehicle must be used during the building a balance process. Things like universal joints, flanges and assembled CV's need to be installed. EVERYTHING from the transmission to the differential needs to operate on a common centerline. The centerline dictated by the u-joint or flange pilot, not the center hole in the spline! That center becomes irrelevant once the rest of the components are installed. Removing vital components like joints, joint caps, and flanges to speed up the process of making a shaft can only lead to errors that will cause vibration.
 
 

A word about Balancing

Balancing a driveshaft was considered by many in the aftermarket to be a waste of time. "We don't get comebacks", or "We build 'em so straight they don't need balancing" are common replies, Fact is, a driveshaft should always be balanced if it operates at speeds over 500 RPM. Even the hard-liners are discovering that there impeccably built shafts are not working as well in today's vehicles. The straightest shaft in the business will be out of balance if the distribution of mass is unequal. 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 shaft. Even a poorly balanced shaft for that matter. Without getting into the long haired formulas, simply remember that IMBALANCE FORCES INCREASE AT THE SQUARE OF THE RPM. (Those forces are what your customer is complaining about!) Simply put, that means that when the RPM is doubled, the is a 4 fold increase in force. Triple the RPM and se 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 driveshaft 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 have a machine that can balance a shaft at actual road speeds. You will then see the increase in vibration due to increase in RPM.

Balancing is a value added service that virtually all of your customers are willing to pay for. Find a way to balance every driveshaft that comes to your shop. If you do not, you are not only doing your customer a disservice, you are leaving money on the table.

Look around your shop. Are you advancing your procedures and methods at the pace that the transportation industry is moving? As technology evolves, tolerances will only get tighter demanding more from your equipment and people. There may be a reason why some shops never get comebacks. That customer may be taking is work somewhere else!

IF THE ONLY TOOL YOU OWN IS A HAMMER,

ALL OF YOUR PROBLEMS BEGIN TO LOOK LIKE NAILS!

A special thanks to Inland Empire Driveline for the above info.