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I want to put something to rest concerning pinion angle, drive line angle, etc...
You will need a digital angle finder, or dial type.
To start this should be done on a drive on lift or with the front tires on blocks or ramps and the axle housing on jack stands trying to keep the car relatively level. There should also be someone in the front seat or weights equivalent to the driver. You should also unhook the rear of the driveshaft. The driveshaft is not needed to set the drive line angle.
To start, if you have and adjustable panhard bar get the rear centered side to side. This is normally done with a plumb bob hanging off the rear quarter panel down past the wheel. Measure from the plumb bob string to the wheel lip. Measure in the same spot on both sides.
Once the rear is centered side to side adjust the axle housing front to back if you have adjustable control arms. If you have adjustable control arms set the both equal off the car first. Then once installed always adjust each one the same amount backwards or forward. Once you are happy with the location front to back it's time to move on to drive line angle. You will probably have to come back to this step of adjusting front to back as adjusting pinion angle will alter front to back location of the axle as well as ride height slightly.
This is where the confusion normally comes in. Setting pinion angle. Everyone seems to measure on the rear angle of the drive shaft and the bottom of the torque arm. For one, that only accomplishes setting the angle of the rear u joint. Secondly the bottom of the torque arm mount is 0.8 degrees off from the actual yoke/pinion angle. What we are trying to set is drive line angle. Setting drive line angle will get rid of vibrations. This is very simple to set. I will explain how to get drive line angle to zero(cancels vibrations) then set the rear for for axle wrap or negative pinion angle.
For all of this lets assume we are looking at the car from the driver side. If you have the car relatively level in the air the motor and trans generally slopes down toward the rear about 2.0 degrees. This can change depending on motor mounts as well as transmission mounts, so don't assume, measure. This measurement is taken on the face of the harmonic balancer. Lets assume the measurement shows up on the angle finder as 88.0 degrees. That is 2.0 degrees(90.0-88.0=2.0) with the motor and trans sloping down toward the rear of the car. Now at the rear end put the angle finder on the face of the yoke and use the adjuster on the torque arm until the face of the yoke is pointing up towards the front of the car at 88.0 degrees. That again is pointing up at the front of the car 2.0 degrees(90.0-88.0=2.0). This is opposite but equal angles and will cancel vibrations. Now if we want -2.0 pinion angle to account for axle wrap up you simply turn the front of the yoke down 2.0 degrees. This would show as 90.0 which is 0.0(90.0-90.0=0.0) in this case. Now when the axle housing wraps up 2.0 degrees the drive line angles will be opposing parallels and vibration free.
Now you will have to go back and adjust front to rear of axle housing until everything is where you want. Always go back and double check the angle on the balancer and yoke after a change.
Now, here are my numbers: The top is race ready with a 1/4 tank of gas and 225 lbs in the front seat and nitrous bottle on the driveshaft tunnel.
You will also notice that my driveshaft runs uphill to rear end. So, if I turned it down as per BMR, the ujoint at the trans and ujoint at the yoke would be fighting each other. But, according to the BMR method I have a +3.3 degree pinion angle. This is not true, the pinion angle is -0.8, as you can see the rear ujoint angle is 3.3 degrees. This will make more sense in the video at the bottom.
Now hear is my same car with a full tank of fuel, single 12 subwoofer, other crap in the back, still 225 lbs in the front seat. Basically daily driver mode. Notice the numbers change with weight in the car. The more weight in the car, the motor and trans start pointing down more towards the rear of the car and the yoke also points down more towards the front of the car. I check all this to make sure I had opposing angles in both race and daily mode. And both are right around -1.0 degrees. If I had set it at -2.0 pinion angle you can see the rear yoke would have gone into a none opposing angle causing a vibe at cruise and braking but probably smooth under acceleration.
I'm glad you posted this! a lot of people need to know! I never knew the torque arm mount was .8 degrees off, good to know! I'll be resetting my driveline angle asap. THIS NEEDS TO BE A STICKY!!!
Though I would not recommend using an analog angle finder unless you have a very good one. if you are not looking at them exactly perpendicular it can skew your findings.
Trying to understand your drawing- I totally understand the video.
How much difference in angle from the front u-joint do you allow at the rear joint? IE, how much axle deflection do you get while driving? Do you want a -0.8 degree difference front to rear to allow for axle wrap? And is axle wrap based on LCAs, springs, shocks etc, or is it pretty standard for any setup?
Stock LCA with stock rubber bushings. Stock tq arm. Car is for autocross and sunny day driving/corner carving. I have strano springs (lower about 3/4 inch I think) and koni yellow sport shocks.
Thanks. :-)
I might have to get an adjustable torque arm.
So my trans is out right now and I've never had a problem before, but since I'm doing a lot of upgrades this winter I may as well double check it, and know how to fix it before I put many miles on.
What would you set it with a t56, UMI long torque arm, Lcas, phb, lowered on stranos and bilsteins? I have it at what I believe is -1.5. Measuring it the wrong way I guess so who knows what it is.
So basically you measure the front hub and the yoke and get them at the same angle (so that they make a parallel line vertically?) then just back the yoke down to a negative degree?
This is the first explanation I've ever read on setting pinion angles that actually makes sense to me. So thank you my good sir! Now that I've said that, I looked at your drawings and that part completely lost me, too many numbers and arrows for me. I decided to make my own drawing and hopefully I can try to explain what you meant to get across in your drawings.
For my drawing I used the the angle 87.4 degrees measured at the harmonic balancer. If we draw a line perpendicular to that angle, we get 2.6 degrees sloping slightly downwards (hence why I wrote 87.4 degrees or 2.6 degrees.) Now since the 1st u-joint angle mimics the harmonic balancer's angle, we just use the harmonic balancer's angle for the 1st u-joint angle measurement. The 2nd u-joint angle, measured by the face of the yoke at the rear end (credit to jblankenship) is 89.4 degrees or again if we draw a line perpendicular to that angle, we get 0.6 degrees sloping slightly downwards to the rear of the car, or to the right. These two angles have a difference of -2 degrees (2nd u-joint angle - 1st u-joint angle, or 0.6-2.6 = -2) The -2 degrees accounts for the axle wrap-up/hard acceleration, which would then theoretically make your pinion angle 0 degrees. - This is better explained in my second picture if you can make sense out of my drawings.
This picture is basically an exploded view of the harmonic balancer and rear end yoke of the first drawing with some extra visuals. On acceleration the rear end twists upwards giving you the 2.6 degrees that would make the pinion angle perfectly aligned in this case (notice how the two dotted lines are parallel which means that they're not counteracting each other.) Hopefully this drawing is decipherable
Thanks to jblankenship for the explanation and hopefully this can aid someone in the future
Last edited by Corvett z07; 01-31-2016 at 06:11 PM.
To figure out ujoint working angles you will have to measure the drive shaft angle. That measurement is then compared to the yoke or balancer measurement.
These drawings are great. Finally a simplified version of how to set correct pinion angles. One question though, is everyone just assuming that axle wrap can be accounted for by setting to -2*? Is this like a known thing? I just want the vibes to stop lol. Im going to throw my car up on four rhino ramps and have at it with this method and see what happens.
01-24-2016, 07:08 PM
How to properly set rear end angles inside 
.... 
Now that I've said that, I looked at your drawings and that part completely lost me, too many numbers and arrows for me. I decided to make my own drawing and hopefully I can try to explain what you meant to get across in your drawings.
