Tek Tips Driveshaft Angles

My First Article is going to be on Driveshaft Angles.

Driveshaft Angles

        The following information applies to street rods that are driven on the street by drivers                  who travel for fun and appreciate comfortable rides.

            I found this bit of info floating about and hijacked it from Street Rodder dot com   everybody can have their credit for the article. I am putting it up here and  if anyone has a  snit fit about the article drop me a note  Ok let’s learn driveline 101

 By Greg Frick

  Drive train setup continues to be a baffling and controversial subject. It's baffling because it's three-dimensional, and it's controversial because differing applications require differing solutions. Quarter- and eighth-mile drag or oval track race cars have different setup requirements than cars used on the highway. The following information applies to street rods that are driven on the street by drivers who travel for fun and appreciate comfortable rides.

Why do we have to think about these angles at all? We wouldn't if the engine, transmission, driveshaft, and pinion all shared the same centerline. As it is, these components are never on the same centerline, so universal joints are used to get power around corners. Unfortunately, as the front U-joint gets the power delivered to the driveshaft, it transforms smooth engine power into pulsating power. This happens because the U-joint travels an elliptical path caused by the angle through which it operates. You can visualize this by looking at a dinner plate straight on. If you tilt it the round plate appears to become an ellipse. In traveling this ellipse, the U-joint speeds up and slows down twice per shaft revolution. A second U-joint having an equal but opposite angle is used to convert this pulsating power back into smooth power feeding the pinion. The bigger the working angles are, the more violent these speed changes become

The Dana Corporation's Spicer Driveshaft Inc., publishes charts showing joint bearing life versus joint working angle at various rpm. It has been our experience that street rodders will be aware of a general busyness in the car caused by joint angles greater than about 3 degrees. The busyness is felt because engine power in the driveshaft is always pulsating power. Here are three examples of working angles of 3 degrees or less.

Figure 1

                                                     Engine 3 degrees down                         Working angle A=3-0=3

                                                     Rear End 3 Degrees up                         Working Angle B=3-0=3 

                                  Drive shaft = 0 Degrees                        Un-Cancelled Angle =0

Figure 2

                                    Engine 1 degree down                          Working Angle A=1+2=3

                                                       Rear End 1 degree up                           Working Angle B=2+1=3

                                                       Drive Shaft 2 Degrees up                     Un-Cancelled Angle = 0

Figure 3

                                                      Engine 3 Degrees Down                       Working Angle A=3-2=1

                                                      Rear End 3 Degrees Up                       Working Angle B=2-3=-1 

                                                      Drive Shaft 2 Degrees Down                Uncanceled Angle =0

As everyone knows, a pinion moves, especially in leaf-spring cars. On a street driven vehicle, the goal is for the pinion to move equally on either side of ideal to produce an acceptable compromise for driver comfort. Deliberately placing the pinion at a lesser angle than ideal is common on the drag strip where power is always full on. Using such a setup on the street will result in an annoying vibration every time you back off the throttle. During long downhill runs with the engine braking this will be particularly aggravating.

 Street rods are nothing if not stylish. Sometimes a car's design will clash with the functions required for drivability. What are the consequences of bending or ignoring the functions described above?

 Uncanceled U-joint working angles deliver pulsating power to the pinion, ring gear, axles, and wheels. Resistance from the ground causes these pulsations to feed back up the power train, contributing to vibrations in seats, mirrors, gearshift levers, and other miscellaneous parts. The pulsations can also destroy parts like transmission clutch packs, tail shaft housings, rear-end bearings, gear sets, and axles. Figure 4 shows a real world example.

Figure 4

                Engine 6.5 Degrees Down                 Working Angle A=6.5-0=6.5

                Rear End 0 Degrees                      Working Angle B=0-0=0

                Drive Shaft 0 Degrees                   Uncorrected Angle=6.5

*** Some Notes on Thrust angle and driveline Alignment.

Ok I know somebody is going to question my use of the word thrust angle. To me it is simply a straight line through the crankshaft center and center of the transmission shaft Pinion thrust angle is used in the same way.

This came up during a recent Bovine Scatology session out in the shop. We were discussing a certain vibration a friend was having. The guy had checked everything and was looking for a new angle to solve the problem. (Bad Pun).

Out of that discussion a possible source of the vibration has been noted and I made some quick paint drawings to illustrate my explanation.

We feel the problem could possibly be a misalignment of the pinion centerline and the power plant centerline. This vehicle has recently had a engine, trans, and rear end transplant. Due to this fact we feel it is possible but not definite that the thrust centerlines of both the engine/Trans and pinion centerline may not be parallel or aligned with other. They don't have to be in alignment they just have to be parallel to each other to keep that uncorrected angle as close to zero as you can.

Keep in mind that this is the rating's' of a bunch of over educated Non politically correct, self described high tech motor heads.

Figure 1 shows a harmonious alignment of the power plant and pinion thrust centerline. This is a perfect world scenario.

Figure #2 Shows an offset pinion and as long as the parallel relationship of the thrust lines remains, everything will be just fine.

Figure #4 is a crude representation of a misaligned pinion to engine thrust line. In this case I was trying to illustrate what happens when the pinion thrust line is not parallel.  I have shown just the rear end misaligned. The engine transmission package could just as well be at fault. If the engine is mounted at an left or right angle you will have the same misalignment.

The whole idea of this thrust misalignment comes about by a discussion of higher speed vibration a person was experiencing in their car. All of the standard angles were good and this is where we would start the next round.