Pinion Angle

[‘Ol Flossie]

I have a C10 LWB and have flipped the axle with a Western Chassis kit. With the drive shaft out, I’ve measured -4 degrees (86) at the transmission tail shaft. At the pinion, I’ve measured 0 degrees (90). I have the axle on jack stands. Does that affect the angle reading? If not, would I want to shim -4 degrees from the rear of the axle to have the pinion pointing downward or +4 degrees having the pinion pointing upwards?

Thanks in advance

[‘Ol Flossie]

I think I incorrectly stated my angle at the trans tail shaft. I believe it is 94 degrees rather than 86.

[frotosride]

I was going to type a lot of stuff out but this is so much easier on my fingers... oh, put on your sandels, there's math involved!! 

[‘Ol Flossie]

Today I took the axle off the jack stands and found that the measurements do change with the wheels on the ground. I have +3.5 degree angle at the pinion and had -5 degrees at the transmission tail shaft. I shimmed the transmission up 1.5 degrees. I measured the driveshaft angle and come up with -2 degrees. Adding the angles of the driveshaft and pinion together for a total of 1.5 degree pinion angle, which I think falls into tolerance. Does it sound as though my thought process is correct? So many differing opinions or explanations that I’ve read, I’m not confident that I’m viewing this correctly. I failed to mention earlier, though not sure that it matters, this is an ‘84 model long bed.

[‘Ol Flossie]

I was going to type a lot of stuff out but this is so much easier on my fingers... oh, put on your sandels, there's math involved!! 

I can do math. Do you have any info that can help me?

[JohnnyPopper]

I spoke to the pro at Gearvendors and he said the max you want is 6 degrees at your transmission.

[frotosride]

I was going to type a lot of stuff out but this is so much easier on my fingers... oh, put on your sandels, there's math involved!! 

I can do math. Do you have any info that can help me?

Sorry i forgot to put in the link.....

https://www.drivelinesnw.com/part-trouble-shooting/vibration-analysis/angle-analysis/measuring-and-correcting-angle-problems/

[VileZambonie]

Only measure with the tires on the ground, jounce the suspension and make sure you have wheel chocks in place because you are going to need to nudge it forward or backward to get the flat spot on your yokes parallel. I use a pinion angle gauge that attaches to the u-joint cup magnetically. You can use a protractor too but the pinion angle gauge is nice to have. I hear so many people saying on Fakebook and all over the web, not to reposition crossmembers or space the trans mount but that's all BS. Just remember, garbage in, garbage out. If you aren't getting good measurements you'll be chasing your tail.

[‘Ol Flossie]

Only measure with the tires on the ground, jounce the suspension and make sure you have wheel chocks in place because you are going to need to nudge it forward or backward to get the flat spot on your yokes parallel. I use a pinion angle gauge that attaches to the u-joint cup magnetically. You can use a protractor too but the pinion angle gauge is nice to have. I hear so many people saying on Fakebook and all over the web, not to reposition crossmembers or space the trans mount but that's all BS. Just remember, garbage in, garbage out. If you aren't getting good measurements you'll be chasing your tail.

Thanks for all the helpful intel everyone. I think I finally get it. @ frotosride, I had read the write up in the link you provided a couple of times prior to you sharing, but it never made sense until I watched the video. My minds eye was playing tricks on me with the angle relationship and the way I was studying the angles. I was looking at the angles in two different perspectives. I looked at the angle from the differential housing from rear to front and the angle at the transmission from front to rear. The video taught me to either look at the angle from transmission to rear end and think of both angles as being down, or think of the angle as being up when looking at it from rear end to transmission. That’s why I felt as though I was getting conflicting information. When looking at the rear end and which way I should angle pinion, I thought it should be in the upward position, but got really confused when I would read the the angle should be down. It’s all about perspective.