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Discussion Starter · #1 ·
I've got a pretty bad vibration on decel in my 63 Nova. It has a 12 bolt, anti roll bar, and caltracs. So I now have several questions after doing some "research".

1. What is the proper way to measure for pinion angle?!

2. How is the pinion angle adjusted with a leaf spring car?

I measured my junk and came up with -7.5* by measuring the driveshaft and the yoke on the yoke. If that's not right, then I don't know what the fuck I have. I do know on acceleration there is no vibration and it leaves straight. However on decel on anything over 50mph, it vibrates badly.
 

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its measured at the yoke on the trans and the yoke on the pinion . Take the driveshaft out of the equation .

Its adjusted with welding the perches on the axle or with shims if you dont want to start over with the perches .

Im at -2 on my caltrac setup .
 

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Best way to measure pinion angle is with the wheels on the ground measure the harmonic balancer angle and then the pinion yoke angle. If they are at the same angle you have 0* pinion angle. Using the trans tail or measuring the driveshaft just makes it confusing.
 

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Discussion Starter · #7 ·
Alright, I remeasured with the car on the ground. The balancer/driveshaft angle are opposing angles to the yoke.

-balancer angle 2.5*
-driveshaft angle 1.75*
-Yoke angle 7*

So I should try a 2* shim?
 

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Gigity
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Alright, I remeasured with the car on the ground. The balancer/driveshaft angle are opposing angles to the yoke.

-balancer angle 2.5*
-driveshaft angle 1.75*
-Yoke angle 7*

So I should try a 2* shim?
I assume the engine is tilted down toward the rear, the driveshaft runs downhill toward the rear, and the pinion is pointed down towards the front? Is this accurate?
If that is true, it looks like you have 4.5* of pinion angle, which is OK, but the pinion to driveshaft working angle is 8.75* which is the reason for your vibration on decell.
If I were you, I would try lower the rear ride height a little. Then I would shim the trans mount up a tiny bit to try get the driveshaft closer or larger than the engine angle.
If lowering the ride height is not something you want to do, you will need to move the engine/trans
 

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Alright, I remeasured with the car on the ground. The balancer/driveshaft angle are opposing angles to the yoke.

-balancer angle 2.5*
-driveshaft angle 1.75*
-Yoke angle 7*

So I should try a 2* shim?
Balancer is 2.5* up? Yoke is7* up or down??? If your balancer is up as it should be and your yoke is down 7* you have 9.5* negative pinion angle, not good.
 

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Chief Curmudgeon
1969 Pontiac Firebird
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Proper alignment diagrams


Add a more down angle on pinion for higher HP drag racing installations




Add a more down angle on pinion for higher HP drag racing installations

:rolleyes:
 

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Discussion Starter · #11 · (Edited)
I assume the engine is tilted down toward the rear, the driveshaft runs downhill toward the rear, and the pinion is pointed down towards the front? Is this accurate?
If that is true, it looks like you have 4.5* of pinion angle, which is OK, but the pinion to driveshaft working angle is 8.75* which is the reason for your vibration on decell.
If I were you, I would try lower the rear ride height a little. Then I would shim the trans mount up a tiny bit to try get the driveshaft closer or larger than the engine angle.
If lowering the ride height is not something you want to do, you will need to move the engine/trans
Yes, this is correct. I ordered a 2* shim and was going to give that a go. There is already a lowering block on the rear, not really sure how much I can safely lower and still get the wheels out of the wheel well. It did cross my mind to raise the trans, but I wasn't sure how that would affect the angle without adjusting it with the shim as well.
 

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Alright, I remeasured with the car on the ground. The balancer/driveshaft angle are opposing angles to the yoke.

-balancer angle 2.5*
-driveshaft angle 1.75*
-Yoke angle 7*

So I should try a 2* shim?
correct me if Im wrong , but it would take putting the pinion at 0 degrees to get a -2.5 pinion angle .

If this is correct , I would be getting a new set of perches and start over .
 

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Gigity
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If you already have lowering blocks, I do not recomend the tapered shims at all. You can never get the u bolts tight enough for the rearend to stay put. I would cut the perches off the diff and start fresh.
Or consider de-arching the springs, this will reduce pinion angle AND let you remove the blocks.
 

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Discussion Starter · #14 ·
If you already have lowering blocks, I do not recomend the tapered shims at all. You can never get the u bolts tight enough for the rearend to stay put. I would cut the perches off the diff and start fresh.
Or consider de-arching the springs, this will reduce pinion angle AND let you remove the blocks.
The lowering blocks aren't a deal breaker. I'd like to get out of this without removing the perches. I ordered a 2* and a 4*. Sounds like the 4* is what I should try, no? I'm fairly certain that the blocks are billet and the shims are billet, just throwing this out there, welding them together a no-no? The shims have cutouts throughout them so it wouldn't just be on the edge.

My reasoning for not wanting to cut the perches off is because it leaves straight and the only problem is the vibration. If this sounds like I'm out to lunch, please let me know.
 

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I assume the engine is tilted down toward the rear, the driveshaft runs downhill toward the rear, and the pinion is pointed down towards the front? Is this accurate?
If that is true, it looks like you have 4.5* of pinion angle, which is OK, but the pinion to driveshaft working angle is 8.75* which is the reason for your vibration on decell.
If I were you, I would try lower the rear ride height a little. Then I would shim the trans mount up a tiny bit to try get the driveshaft closer or larger than the engine angle.
If lowering the ride height is not something you want to do, you will need to move the engine/trans
If the engine is tilted down toward the rear and the pinion is pointed down at the frt this setup has waaaay too much downward pinion. 2* isn't going to do anything. If the engine tilts down at the rear 2.5* the rear has to point up 2.5* to have zero pinion angle.
 

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Gigity
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If the engine is tilted down toward the rear and the pinion is pointed down at the frt this setup has waaaay too much downward pinion. 2* isn't going to do anything. If the engine tilts down at the rear 2.5* the rear has to point up 2.5* to have zero pinion angle.
Why did you quote me?
Nowhere have I Suggested 2* anything
 

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Pinion angle is simply the difference between the angle of the drive shaft and the pinion shaft. Ideally you want 0 degrees at full power. Most suspensions use about 2 degrees down angle at rest.
^^^^ X2, forget the driveshaft, take it out of the car if it makes it easier for you.

I run 3 degrees in my split mono caltrac setup, driveshaft rpm is 9000 through the lights, no vibration
 
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