Pinion angle - have a vibration

[Mopar to ya]

I know there has been posts of this before, but I never see the actual numbers. I have had a high speed vibration for years. I have had the driveshaft balanced many times. Checked all the usual suspects. I started to wonder about my pinion angle. On the hoist it looks good, but I never checked on the ground. That was a "duh" moment. My buddy Tom has an angle gauge and we checked. The pinion angle is 3 degrees and the transmission angle is 2 degrees, all while flat on the ground. I would have to believe these numbers are very good, but I don't know exactly what they should be. Anyone able to help out here and give me an idea of where I should be? Oh yeah - small block 408, 200R4 transmission and Dana 60. I also have Caltracs and Calvert Racing mono leafs.

 

[Treblig]

I fought this problem also and after some research I found this:

http://www.moparts.org/Tech/Archive/axle/8.html

At the end of the article it also gives you the angles using different rear end set-ups. I ended up happy with my pinion angle 1 1/2 degrees lower than my trans angle. I guess, depending on how stiff your springs are, the amount your pinion rises (under load) probably determines how much you should be "below" the trans angle. If I read this article correctly what you want is for your angles to be the same when the rear is under load (centerline of pinion parallel to centerline of trans). Unless your rear end is mounted completely solid it should rise (the pinion anyway) under load, the amount it rises will vary with each different set-up.

Hope this helps.
LOVE MY 2004R!!!!!
Treblig

 

[Mopar to ya]

But how can you possibly know how much it rises under load? Any way to measure that? I'll update my original post to add that I have Caltracs and Calvert Racing mono leafs.

 

[68gtxman]

It is so easy to add wedge shims under the spring perches to test an angle adjustment. Just buy a few shims of different angles (Jegs or Summit has them) and pop them in from smallest to next one larger. Take a test ride after each and see if the problem is better or worse.

BTW, the angles are trans rear = up and diff. nose. = down. If they are both up or both down, then you will have a very bad vibration. (was that a Beach Boys song?rotest

 

[Locomotion]

Cal-Tracs normally call for very little down pinion angle and using SS springs, which can provide a lot of rise, call for as much as 6*. As mentioned, shocks also have an influence on rise/seperation.

Here is an old thread on the subject.
http://www.forabodiesonly.com/mopar/showthread.php?t=160127

FWIW, a while back I had a vibration and it turned out to be a spread yoke. You could actually manually feel the driveshaft move up & down in the saddle, just a tiny bit, even though it was all installed correctly. But it was enough to spit the driveshaft out on the next run. Went to billet yokes ever since.

 

[Treblig]

But how can you possibly know how much it rises under load? Any way to measure that? I'll update my original post to add that I have Caltracs and Calvert Racing mono leafs.

Depending on how your rear end is set up and or how soft your springs are it will vary of course that's why the article I posted tells you how to determine whether to move the pinion up or down:
" If you accelerate and get a vibration OR your vibration increases then your pinion is too high. If you decelerate and you get a vibration OR an increase in vibration then your pinion is too low."
It took me a couple of tries (with different angle shims) to get the vibration to stop. But that's why the article gives these rules because it's really hard to see and measure how much your pinion rises when you're accelerating. There are many videos on u-tube where people have mounted a camera under their car to show how much the pinion rises and the videos show lots of variation depending on spring rates, spring lengths, ladder bars, 4-link, etc. Some pinions rise a whole bunch while some hardly any at all. I would recommend you start with making sure your pinion angle is maybe 1 degree less (down) than your trans angle (with the car sitting on the ground) because you know it's going to rise at least 1 degree if you have leaf springs. You know the pinion will rise but until you drive around and accelerate and decelerate with the new pinion setting you'll never know. You know for sure that if you make the angles equal it's still going to rise under acceleration just because of the load so you need to start below that point somewhere. GOOD LUCK and make sure lube those u-bolts.

PS - I used the solid metal shims that bolt to the springs this way they can't move or break like the cheap cast aluminum ones, in fact, I think I have a few sets left over (the ones that were the wrong angle):


Treblig

 

[Supershafts]

I take it the trans is 2 degrees down and the diff is 3 degrees down.

under load the diff is going to go 2 to 4 positive, which should be ok.

You'll need a vid cam to watch it, or a drive on lift and straps to ideally set it.

You want 0.0 angle on any performance app.

.

 

[Treblig]

What ever happened with the pinion angle/vibration problem???? Inquiring minds want to know!!!!!!!

treblig