[Alfons]

There have been a number of threads started in the last while discussing issues related to DS geometry, including the use of Degree Shims. I've provided a written description of the various configurations, how they work & how to line them up, but my written word isn't always understandable, so I thought I'd post some pictures that lay out the basics of using single and double cardan joints.

Cardan joints are generally used in pairs to end up with a constant velocity output for a constant velocity input, and this first picture shows the critical items that need to be addressed - angle at each end and the yoke ears.



This all relates to the "standard shaft" as shown in this picture:



This picture shows the use of a double cardan constant velocity (CV) joint at the t-case end of the shaft and a single cardan joint at the pinion end. This is a typical rear drive shaft application and keeping in mind my statement that it takes two single cardan joints, set up properly, to give you a CV output you can see that the double cardan joint is really nothing more than two single cardan joints with a centering mechanism to give you the configuration shown in the middle of the first picture. The single cardan joint sitting at the pinion end needs to point at the t-case because it's sitting there all alone and doesn't have a second joint to make sure you get a CV output - that's why you need a small angle there.



There's one more typical configuration & this applies to front axles that have large angles to contend with and because you can't just use degree shims to adjust the pinion end U-joint (changes the caster angle), you need to add another double cardan joint at the pinion end to do the trick & now you can set up the front any way you need to and get the proper steering geometry along with proper drive shaft geometry. I don't have a picture of this configuration currently but will post one here when I do.

[Jim93YJ]

Good info...Hope this is not hijacking your thread but...Another interesting driveshaft tidbit is when I worked with Dynatrac to get my new rear axle they asked me for the:

1)Spring plate angle
2)Vertical Distance of Center of transfer case output yoke to ground
3)Horizontal Distance of Center of transfer case output yoke to Center of Rear Axle
4) Vertical Distance from Center of Axle to the Ground

From that they theoretically calculated what the pinion angle should be....I am a little sceptical and have tried asking exactly what formulas they are using and what exactly is going on, but I have not gotten a response back...maybe someone here knows what they are doing??

[sentinal02]

Originally Posted by Jim93YJ

Good info...Hope this is not hijacking your thread but...Another interesting driveshaft tidbit is when I worked with Dynatrac to get my new rear axle they asked me for the:

1)Spring plate angle
2)Vertical Distance of Center of transfer case output yoke to ground
3)Horizontal Distance of Center of transfer case output yoke to Center of Rear Axle
4) Vertical Distance from Center of Axle to the Ground

From that they theoretically calculated what the pinion angle should be....I am a little sceptical and have tried asking exactly what formulas they are using and what exactly is going on, but I have not gotten a response back...maybe someone here knows what they are doing??

sounds like they know what they're doing to me. 2 minus 4 would give them the vertical difference in the drive shaft ends, 3 gives them the horizontal distance, and 1 will tell them any angle that might already be in play that they have to compensate for. it's fairly simple geometry once you draw it out. if X is your pinion angle, then using your numbering system above

tan x = (2-4)/3

tangent is opposite over adjacent

then solve for x and add or subtract 1 to compensate for the perch angle. simple

[foggybottombob]

There ya go. I always use trig to predict what my final angles will be when I have to rotate a pinion after changing from one axle type to another. It gets pretty close to the final result just doing it on paper.

[Alfons]

Here's a link to an easy angle calculator:

http://www.carbidedepot.com/formulas-trigright.asp

[Jim93YJ]

The problem is I thought they were using simple trig as well but they are coming out with a different answer than what I am getting and I took enough math between highschool and college to know I am doing it right.

But sentinal02 has a point that I did not take into consideration and it hit me once I am seeing it written, is if you subtract the perch angle then that will affect your pinion angle. The problem is I have a spring perch that is point downward toward the front by 2 degrees. Working out the trig my pinion angle minus correction for the perch is 12.65 Degrees. If the perch is downward toward the front then I believe I should either

1) Weld the perch at a 2 degree angle downward with the pinion angled at 12.65 Degrees and cancel any pinion angle change associated with the perch

OR

2) Weld the perch horizontal, with the pinion at 14.65 degress and it would subtract down to 12.65 once the axle was installed on the springs

BUT....Dynatrac told me to subtract 2 degrees not add from my 12.65 degrees to get the correct pinion angle...i.e. 10.65 degrees. That seems opposite from what you should do...am I missing something????

[Alfons]

If you look at the picture with the CV and you see where it states 0 degrees for the angle at the pinion joint? That's for the cruise condition - the 2 degrees down is for the static condition and the axle turns about 2 degrees up when driving to give you the straight line through the drive shaft into the pinion.

I would first see if the pinion shaft and each spring perch are on a parallel plane and if yes, I'd assume that to be the horizontal. If the aren't parallel, then you need to determine how much they're off and in which direction. Next, I'd take all my measurements and draw the drive shaft "angle of the dangle" diagram. In this diagram, the hypotenuse will be a close approximation of the drive shaft if you've included the protrusion of the yokes at the t-case and pinion into your calculations. To calculate the perch setup angle or degree shim size requirements, you would take the angle from the horizontal to the hypotenuse, subtract 2 degrees and then apply any variance that you got between the pinion shaft and the spring "perch plane". When everything is assembled, you would then have the pinion shaft at 2 degrees off with relation to the drive shaft.

Keep in mind that this 2 degrees is just a rule of thumb and not an absolute, measuring devices we use aren't overly precise in some of these applications, and that the suspension will sag etc., so measurements to the nearest degree will be more than adequate.

[Jim93YJ]

Thank you alfons...just to clarify in my previous post I was not taking into account the 2 degrees below pointing directly at the driveshaft the pinion should be when at static condition...I was just mentioning the spring perch for me is two degress downward toward the engine from horizontal.

My point in the previous post was that I believe that 2 degree variance for my spring perch should be added to the trig calculations not subtracted like Dynatrac wanted me to do since the perch is pointed downward toward the engine. Wanted confirmation on this or a rebuttle

[Alfons]

I believe you're right. Here's a simple picture with the pinion shaft and spring perch plane parallel to the horizontal, in this picture, if you moved the axle by the amount of angle A, the pinion would approximately point at the flex point center of the t-case output joint. To move it enough to be good in the static condition, you'd move it (A-2) degrees, however in your case, where the pinion is pointed about 2 degrees below the horizontal, you'd need to turn the axle approximately "A" degrees. If you only moved yours by (A-2), the pointing angle would end up being (A-4) degrees.

[Jim93YJ]

Thaks alfons for the great pic and confirmation!!

Jim

[sentinal02]

Originally Posted by Jim93YJ

Thaks alfons for the great pic and confirmation!!

Jim

yeah, would have to agree with alfons. though i find it strange you're pointing down at the pinion unless it was set to compensate for the spring wrap already which is what you're doing with the -2 degrees. in order for it to point down, your whole drive train would also slope down toward the front of the jeep in the stock setup

[Dmax5er]

Originally Posted by Alfons

If you look at the picture with the CV and you see where it states 0 degrees for the angle at the pinion joint? That's for the cruise condition - the 2 degrees down is for the static condition and the axle turns about 2 degrees up when driving to give you the straight line through the drive shaft into the pinion.

I would first see if the pinion shaft and each spring perch are on a parallel plane and if yes, I'd assume that to be the horizontal. If the aren't parallel, then you need to determine how much they're off and in which direction. Next, I'd take all my measurements and draw the drive shaft "angle of the dangle" diagram. In this diagram, the hypotenuse will be a close approximation of the drive shaft if you've included the protrusion of the yokes at the t-case and pinion into your calculations. To calculate the perch setup angle or degree shim size requirements, you would take the angle from the horizontal to the hypotenuse, subtract 2 degrees and then apply any variance that you got between the pinion shaft and the spring "perch plane". When everything is assembled, you would then have the pinion shaft at 2 degrees off with relation to the drive shaft.

Keep in mind that this 2 degrees is just a rule of thumb and not an absolute, measuring devices we use aren't overly precise in some of these applications, and that the suspension will sag etc., so measurements to the nearest degree will be more than adequate.

Alfons, I apologize for my stupidity, I'll be the first to say, WHAT??? I know other people are reading this and trying to understand, as i am ,,,so ill be the first to admit i don't quite understand all the terminology. I'm doing the 8.8 axle swap in my YJ and I'm down to trying to get the pinion angle. I don't have special tools like you have, but i do have an angle gauge from the chopper days.... Please correct me if I'm wrong in easy to read terms for uneducated shade tree mechanics.
With weight of the jeep sitting on the axles, Line pinion and drive shaft straight in line to the tail shaft center point and then drop pinion 2 deg? is that correct?
Now add a traction bar to stop axle wrap into the picture, do you still drop it 2 deg? Thanks for your patients.

[Jim93YJ]

Dmax5er,

That should toatlly be correct...my problem stemmed from the fact that I did not have a rear axle yet and it was being built. The builders needed to theoretically calculate the pinion angle because they did not have my jeep in front of them to do what you are doing. As a result other factors come in to play when theoretically calulating the pinion angel like spring perch angle.

[Alfons]

Originally Posted by Dmax5er

Alfons, I apologize for my stupidity, I'll be the first to say, WHAT??? I know other people are reading this and trying to understand, as i am ,,,so ill be the first to admit i don't quite understand all the terminology. I'm doing the 8.8 axle swap in my YJ and I'm down to trying to get the pinion angle. I don't have special tools like you have, but i do have an angle gauge from the chopper days.... Please correct me if I'm wrong in easy to read terms for uneducated shade tree mechanics.
With weight of the jeep sitting on the axles, Line pinion and drive shaft straight in line to the tail shaft center point and then drop pinion 2 deg? is that correct?
Now add a traction bar to stop axle wrap into the picture, do you still drop it 2 deg? Thanks for your patients.

Your assessment is correct, point the pinion at the output shaft and then drop it by approximately 2 degrees (this is only a rule of thumb) - this 2 degrees is intended to come to zero when you have torque applied to the axle (the cruise condition). You handle the output shaft angle with a CV joint such as a double cardan that's capable of operating at that angle.

The traction bar won't keep the axle locked in position, there's still some twist to it - what you're trying to do is to keep the pinion joint as close to straight through as possible when you're driving. The traction bar will help when you step on the accelerator hard, it'll limit the twist to the axle to whatever maximum you have the traction bar set to.