Understanding driveline angles...

[andrewb70]

When it comes to working out proper driveline angles, there seems to be a lot of confusion and varying opinions floating around the Internet. The goal of driveline alignment is very straightforward. Under load, the front and rear operating angles must be equal, opposite, and as small as possible (under 3 degrees), but not zero.


This is a basic diagram from Mark Williams that illustrates what I just wrote:





Since I have the transmission where I want it, and I had the front of the engine where I wanted, I could take some simple measurements to see where I was at with this car.


Unfortunately, one of the measurements that is needed is the angle of the driveshaft. Since I don't have one in place, I thought of a simple way that I could approximate the angle. I measured the CV mounting holes diameter on my slip yoke and I did the same for the rear pinion yoke. The measurements were nearly identical, which means that I could run a string from the bottom of the slip yoke to the bottom of the pinion yoke to approximate my driveshaft angle.


I attached the string like this in the front:





In the rear I attached it like this:





The car is on jack stands in the front, but there rear suspension is on the ground. Having the rear suspension loaded and at ride height is imperative to getting the right measurements.


With the string in place, I got my digital angle finder out, and got the following numbers:


Slip yoke: 8.6* down towards the rear (this makes sense since the car is jacked up high in the front)


Driveshaft (string): 8* down towards the rear.


Pinion: 7* up towards the front.


From the above numbers we get the following:


Front operating angle = 8.6 - 8 = .6 degrees
Rear operating angle = 7 - 8 = -1 degree


Going back to our stated goals, we see that this is a pretty good starting point in a static state. Under power, the pinion will want to climb up and so the rear operating angle will decrease as it travels through it's range of motion.




While I don't technically need the CV joints in this application, I still plan on using them to achieve the smoothest driveline that I can. With the 4.33 rear gear and the 27" tires the driveshaft will be spinning at a hair over 4000RPM @ 75 MPH, so it is critical that all the components are running true (as little runout as possible) and that all of the components are balanced as perfectly as possible.


Andrew