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Most everything I put my hands tells you pinion angle off the face of the 3rd member yoke should not exceed 3 degrees down or 87 off of 90 for street machines. And as long as the trans output angle is the same and both are in phase or parallel, that is what your trying to achieve.
I have more than that and the my driveline is smooth through all the gears and at cruising speed.
Feedback....
 

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The theory is that if the angles at the front and rear of the propshaft are more than 3 degrees out from each other you'll experience premature wear in the UJs. If the facts follow the theory or not I can't say.

Just keep an eye on them, maybe think about a prop loop in the chassis if you don't have one.. ideally placed so that if the rear UJ breaks the prop wont thrash about too much and if the front one breaks it can't dig in the ground and pole vault the car...
 

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Actually the pinion has to point UP to make it parallel to the transmission shaft/engine crankshaft. That is where you want it for vibration free reliable performance.

If the shafts aren't parallel, you will have vibration. That is far worse than premature wear, though I guess that will happen too.

There is a secondary situation here too. Having the shafts parallel is the most important thing. (Actually what you want is equal angles on both u-joints, and there are other geometries that satisfy that. But not usually on a 55-57). When the shafts are parallel, they may still not be in line. If they are not in line, then there is an angle in the u-joint all the time. The bigger this angle is, the more likely you may get a high speed vibration. 3 degrees gets you vibration free to a driveshaft speed of close to 5000 rpm if I rememeber correctly. There's a chart from Spicer somewhere on the internet which gives you a speed vs. u-joint angle vs. driveshaft speed recommendation. Unless you have the rear end jacked up a bunch, you'll usually be 3 degrees or less. This is why 4wd, especially the jacked up ones, have so many driveline problems.

Back to the pinion angle itself. The only thing that is variable here is whether the pinion angle changes with load, and if so, what load should you design for when setting the pinion angle. That change with load is going to be due to spring wrap up. Traction bars will limit that, as will 4 bar and other types of suspensions that don't use leaf springs. If you are building a car to drive on the street, set the pinion angle for the spring wrap you'd expect when cruising (almost none). That will minimize cruising vibrations. If you have a race car, well the real answer is not to have spring wrap up. So either way (if you subscribe to all this) you set the pinion up 3 or 4 degrees to match the trans.
 

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Equal and opposing angles front to back,,with the slight extra "up" on the rear pinion as posted. no more that 1/2° to 3/4° off side to side, as per spicer when I talked to them.

That being posted, I read recently on another board where a guy had 6° up on the transmission, and almost zero degress on the pinion,,without vibration.

I set up the 56 with 2.5° up on the rear pinion and 2° down on the trans tailshaft. you dont want to straight line the pinion and tailshaft alignment, or you will beat the needle bearings out of the ujoint bearing cups. the few degrees you "dail in" allows the needle bearing to rotate, cool and lube, and not get pounded flat. not less than 1° on each end as a general rule.

fwiw
 

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I think this "zero angle" stuff is a non-deal.

First, you couldn't put everything together THAT straight if you wanted to.

Second, there is enough suspension movement that the angle would never stay zero except when the car is parked.

"Equal and opposing" angles are not required. They can be "equal and non-opposing" too. Equal is enough. The angle can be down or up.
 

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I think this "zero angle" stuff is a non-deal.

First, you couldn't put everything together THAT straight if you wanted to.

we did, but fixed it

Second, there is enough suspension movement that the angle would never stay zero except when the car is parked.

"Equal and opposing" angles are not required. They can be "equal and non-opposing" too. Equal is enough. The angle can be down or up.
equal and opposing,,meaning as an example,,6° up on the pinion, should have 6° down (opposing) on the trans side.
 

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Understand. And that was the basis of what I stated.

The trouble with opposing angles when you have stock or near stock ride height is that you have to account for the driveshaft angle too, and it's going to be much greater if you point the pinion down.
 

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drive shaft angle

it is my understanding that the 3 degrees in discussion is the DIFFERENCE between the pinion angle and the eng/trans angle. the pinion is pointed down so when axle torque wraps up the rear springs the pinion and the eng/trans are parallel. this said, I mean parallel, not a straight line. as previously stated this is to keep the u-joints moving. any angle reference to the ground is immaterial, only the pinion and eng/trans.
regards grady
 

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Unfortunately the article is not all that in depth, but the illustrations are excellent.

Case #3 is the one that usually applies to our cars.
 
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