pinion angle

[danadena1960]

I have a 1977 K-20 with a 6 inch lift. What pinion angles do I need on the front end and rear end?
Thanks,
Dana

[kwmech]

Nobody can specifically answer your question because of different variables involved. What you need to do is invest in an angle finder and measure the amount of degrees on the ouput yoke of the t-case. For example lets say 6 degrees. On the rear diff. that amount of degrees ideally needs to be the same so the yokes are parallel [sp], so when the driveline is spinning the angles cancel each other out thus eliminating a vibration. That is in the perfect world. More often than not, with a relatively large lift the rear pinion has to be moved upwards so the u-joint will not bind. So when the t-case is at 6 and you roll the rear axle yoke up you may be able to get away with? depending on the length of the driveline.
Forgot the front-- front shafts are not as critical due to the speed involved when locked up. Concern yourself more with the alignment of the front than your angle

[Scrub]

I am going through the same grief myself. So here is what I have learned:
Assume that the output of your t-case has a constant velocity of 2000 rpm. If it has no angle, a u-joint will spin the driveline at that same 2000 RPM. Once you introduce an angle, the driveline will no longer spin at a constant speed. It will accelerate and decelerate (A&D) to maybe 2050 RPM and 1950 RPM. The greater the angle, the greater the A&D and the number will increase exponentially. (More on that later)
I found a website that will calc your A&D, given an input speed and an angle.
http://www.bgsoflex.com/dshaft.html

How you get ride of this A&D is to have another U-joint at the other end of the driveline that has the same angle as the first u-joint. This is why you normally want to have your t-case shaft and your pinion shaft at the same angle, i.e. parallel. Both the u-joints must be welded to the driveline so the yokes line up with each other. This is why you have to get your splines lined up or the two u-joints can’t compensate for each other. Two u-joints with the same angle will compensate for each other and output a rotation with a constant velocity, 2000 in and 2000 out. That is the theory of a CV joint, or a constant velocity joint. It has two u-joints at the same angle and outputs a constant velocity.

So the second choice in setting up your drivelines is to put a CV joint on your t-case, which will have no A&D output to the driveshaft, and roll your rear axle on the springs so the rear u-joint has no angle and it effectively points right at the CV joint on the t-case.

Right away, the argument will be raised that a u-joint with no angle will wear out really fast, and that is true, but, your axle will move up and down, and you will get slight changes in angle. This turns out to be the most common way to set up a high angle driveline.
The only problem with that scenario is the fact that the biggest CV you can buy it a 1350. If you are happy with a 1350 joint size then this is your best bet.

On the front end, a CV is commonly used because the t-case is at an angle in respect to the frame. Your motor and tranny and t-case all slope downward as everything goes toward the rear. That causes the front output shaft to tilt upward. Remember the old Ford Highboy f-250 trucks with the terrible front drivelines? The front axle pinion had to be parallel to the t-case shaft, so the pinion was pointed down and the driveline was extremely low and they got hit a lot. The CV solved a lot of that problem as the front axle could be rotated up and pointed at the t-case output shaft.

So how much angle can you get away with? Remember that “exponentially” thing?
What it really means is “some number multiplied by itself, one or more times”. 10^2 = 10x10 = 100. 10^3 = 10x10x10 = 1000
As it turns out, low angles have very little speed distortion. The A&D increases by the number that represents the u-joint angle, to the power of some exponent. I don’t know what the exponent is, but let’s just say it is 2. An angle of 1 degree would cause 1x1 A&D, which is 1 and actually causes no A&D distortion. An angle of 2 degrees would be 2x2 = 4. 3 is 3x3 = 9 and so on. 10 degrees is 10x10 = 100. 15x15 =225. As you can see, a low angle has very little A&D distortion. I would say 2 degrees would not cause any vibration, but that means 2 degrees total angle in a u-joint that is pointing at a t-case output. If the 2 degrees is the difference between a t-case u-joint with 12 degrees and a rear pinion u-joint with 10 degrees, then you are in trouble as the 12x12 = 144 and the 10x10 = 100, which is 44 different. Compare that to the 2 degrees total ( 2x2 = 4 ) and you hopefully see that 2 degrees can be huge. Let do another example. 17 degrees and 15degrees. 17x17 = 289. 15x15 = 225. The difference here is 64. As angles get greater, the problem grows exponentially.

I hope this helps, as it is really hard to explain and few people really understand the subject.

http://www.drivetrain.com/driveline_angle_problem.html

[mutant-jimbo]

scrub, i read it and i still dont understand all of it, but did take in part of it. lol
you are hard core

[Scrub]

mutant-jimbo,
Thanks.

I spent over an hour trying to make it understandable but then when I go back and look at it I realize that it is still a really complicated subject and really hard to push across.

Bottom line,
Make your output and pinion parallel or if yu are really steep, point the pinion at the t-case and run a cv joint at the t-case.

[mutant-jimbo]

i understood it all until the last paragraph. the whole mathamatical equation part messed me up. i can tell it took a while to write, as its written very well.