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Discussion Starter · #1 ·
I have run into a snag getting my driveline aligned. I know that the angle of the transmission and the angle of the end yoke have to be about the same. The end yoke is about as parallel to the ground as it can get (I didn't set it up, that's just what I have to deal with). The trans however, is at 4 degrees looking down. The obvious thing to do is to raise the trans to 0 degrees and call it a day. But I can't do that because it is almost hitting the tunnel. Raising it any further would mean cutting up the tunnel and making the trans protrude through into the car.

Here is my situation:
Azure Font Circle Rectangle Logo


I don't want to get into another project of tilting the rear diff up 4 degrees. What can I do to address this issue?
 

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If you want to change it and can't move the tail up, you've only got two other choices....drop the front of the motor, or tip the pinion nose up.

What kind of rear suspension are you dealing with?

Leaf spring is easiest to fix, just use a wedge shim between spring and perch.
Factory 4-link, just get either upper or lower adjustable arms.

Moving front of motor down seems like the most drastic choice and a lot more work.

If it is leaf spring, and depending on how much power you have, it may be fine right where it is....you have to allow for the fact the pinion will rise in reaction to power applied and bends the leaf spring("Axle wrap")
 

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Discussion Starter · #3 ·
If you want to change it and can't move the tail up, you've only got two other choices....drop the front of the motor, or tip the pinion nose up.

What kind of rear suspension are you dealing with?

Leaf spring is easiest to fix, just use a wedge shim between spring and perch.
Factory 4-link, just get either upper or lower adjustable arms.

Moving front of motor down seems like the most drastic choice and a lot more work.

If it is leaf spring, and depending on how much power you have, it may be fine right where it is....you have to allow for the fact the pinion will rise in reaction to power applied and bends the leaf spring("Axle wrap")
I've got leaf spring suspension.
"you have to allow for the fact the pinion will rise in reaction to power applied and bends the leaf spring" - That's a good point. Perhaps not 4 degrees, but in theory, yes, it should rise.

The engine is about 400 hp, but I never race it or anything like that. In fact the very reason I don't is because of how weak the rear suspension is. I will look into that wedge shim suggestion and, depending on how involved that is, may leave this sucker as is.

Thank you.
 

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Old(s) Fart
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I don't want to get into another project of tilting the rear diff up 4 degrees. What can I do to address this issue?
Tilt the rear end up. That's the only practical solution. There are wedges for leaf spring suspension and adjustable upper control arms for coil spring, It's not exactly a "project".
 

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Discussion Starter · #5 ·
"...Perhaps not 4 degrees, but in theory, yes, it should rise ". I might have to take that back. According to this article, in some applications up to 7 degrees of negative angle for the pinion is required. So 4 degrees, as is the case here, isn't even that drastic.
 

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I think the thinnest available shim is 2° if you decide you need to get it a little closer.
With leaf springs I wouldn't try to get tighter than that.
If your not using any traction device I'd leave it.

As far as weak, I know of guys running 8 second 1/4 mile cars with leaf springs, and there are pro racers faster than that.
 

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Race it, Don't rice it!
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4 degrees isn't much considering how much the axle is moving under the car while driving so to be realistic, I'd leave it and check the U-joints more often unless it's a vibrating now.
 

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The idea is that you want the u joints to operate at a slightly different angle because it makes them work the bearings inside. You do NOT want the transmission and the rear end "in alignment" angularly........BUT........you want them operating in the same plane angularly. Not directly in line, just on a common angle. That common angle is during operation, not sitting still.


As torque is applied, the rear end will rotate upward and the angle of the rear changes. You most likely will get a couple of degrees of rotation under normal driving conditions. So if you are 4 degrees lower than the trans and you rotate up 2 degrees , you are pretty close. If you accelerate harder the rear may rotate even more. That makes the extra 2 degrees maybe OK for you. What you don't want is rotating past "zero" and going overcenter on the joints as this can cause them to break. Every car has a similar need but not always the exact same need for best results.

I would try driving the car with the 4 degrees down and see how it drives. If there is any vibration I would try a 2 degree shim.

If you install some type of traction bar that limits the rotation of the rear end, then you need to take that into consideration. If the rear cannot rotate, then you would not want 4 degrees initially.
 

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I'll echo that. You want to match the angle of the planes, but you want at least 1 degree in the driveshaft/ujoints. If you make it all one plane, you are [metaphorically] making a big E-string on a guitar. Easy to make it vibrate. If you put 1-4 degrees of angle in the u-joints, you are effectively separating the one big E-string into three sections making (for example) and A, G, and C-string and the three work to prevent harmonics.

Slope Rectangle Font Parallel Symmetry


Slope Rectangle Font Parallel Plot
 

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The idea is that you want the u joints to operate at a slightly different angle because it makes them work the bearings inside. You do NOT want the transmission and the rear end "in alignment" angularly........BUT........you want them operating in the same plane angularly. Not directly in line, just on a common angle. That common angle is during operation, not sitting still.


As torque is applied, the rear end will rotate upward and the angle of the rear changes. You most likely will get a couple of degrees of rotation under normal driving conditions. So if you are 4 degrees lower than the trans and you rotate up 2 degrees , you are pretty close. If you accelerate harder the rear may rotate even more. That makes the extra 2 degrees maybe OK for you. What you don't want is rotating past "zero" and going overcenter on the joints as this can cause them to break. Every car has a similar need but not always the exact same need for best results.

I would try driving the car with the 4 degrees down and see how it drives. If there is any vibration I would try a 2 degree shim.

If you install some type of traction bar that limits the rotation of the rear end, then you need to take that into consideration. If the rear cannot rotate, then you would not want 4 degrees initially.
Most street cars are engineered with equal/opposite angles at rest. During any high performance acceleration when the axle might wrap, you probably don't care about vibes, and the mismatch doesn't account for enough of its duty cycle to be a concern for reliability. Max effort drag cars usually try to keep the pinion angle low so it "wraps up" to the proper angle during acceleration since 99% of their lives are spent at full throttle.
 

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Help me out here. Are your 4 and 0 degree measurements relative to the driveshaft? A drawing including the driveshaft would help. Hopefully you're not using the garage floor as zero degrees, right?
 

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Google
Tremec toolbox

Install the android app(its free)

The thing has a angle finder that lets you use your phone.

You use the balancer as the engine angle, the driveshaft(if you have it), then the pinion or axle with the diff cover removed.

It gives you good information for free using your phone.

Here is a snapshot of one of my results.
Font Watch Electronic signage Gas Display device
 

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Josh posted a diagram of what he has right in the first post.
Only thing missing some of you guys are asking for is driveshaft angle, so that you can figure working angle out.

I'm betting it's good but should still be checked.
 
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