driveshaft angles

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str12-340

str12-340

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I have a cyclic vibration in a totally new drivetrain that I would usually associate with a problem in driveshaft angles. If I put the car on a lift and adjust things so that the transmission pan rail is flat, the angle of the 8 3/4 rear chunk as measured at the mounting pads for the pinion snubber is 3 degrees down. This is NOT a RACE CAR. The priority is to have a smooth ride on the highway. Is 3 degrees enough to cause this? Should I be striving for them both to be 0 degrees (parallel).

If so, can anybody suggest a source for angle shims for the spring pads?
 
The rear U-joint should be 5-7 degs nose down with you in the drivers seat
 
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str12-340 said:
I have a cyclic vibration in a totally new drivetrain that I would usually associate with a problem in driveshaft angles. If I put the car on a lift and adjust things so that the transmission pan rail is flat, the angle of the 8 3/4 rear chunk as measured at the mounting pads for the pinion snubber is 3 degrees down. This is NOT a RACE CAR. The priority is to have a smooth ride on the highway. Is 3 degrees enough to cause this? Should I be striving for them both to be 0 degrees (parallel).

If so, can anybody suggest a source for angle shims for the spring pads?
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What kind of lift? It needs to be on a 4 post where the wheels are.at ride height (2 post will have the suspension drooping)

Remember what I said in my PM. The trans angle and the pinion angle need to be the SAME but opposite angles. IE: if pinion is infact down 3 degrees, that would be -3* trans needs to be up 3*

What is the trans angle? "Flat" isn't a measurement.
 
Flat equals 0 DEGREES. The car is on a 2 post lift with tall jack stands under both rear axle tubes screwed up until the frame is off the lift so all the weight is on the springs. So the trans is at O degrees and because of the A500 trans cross member and close clearances in the trans tunnel it would be hard to change. That leaves shimming the axle up 3 degrees to make them parallel.
 
You measure the transmission angle from the flat area at the output shaft seal, not the pan. Do you have a Mopar Performance suspension manual?
 
I'm not measuring from the pan, but rather the cast rail that the pan attaches to which (oddly enough) is perpendicular to the bell housing.
 
str12-340 said:
Flat equals 0 DEGREES. The car is on a 2 post lift with tall jack stands under both rear axle tubes screwed up until the frame is off the lift so all the weight is on the springs. So the trans is at O degrees and because of the A500 trans cross member and close clearances in the trans tunnel it would be hard to change. That leaves shimming the axle up 3 degrees to make them parallel.
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I'm not sure if having them both at 0 is ideal. I've always understood both the same.but opposite. Can you bring the tailshaft DOWN degree or two? Then bring the pinion UP?

What trans mount did you end up using? I know the poly mount is quite a bit taller than the GM factory two bolt.
 
I found a rubber insert bushing. Moving the trans down would make the mismatch worse and I can't move it up for reasons that I am very sure you understand.
 
Moparts has a good tech article on setting the pinion angle properly.
 
plumkrazee70 said:
What kind of lift? It needs to be on a 4 post where the wheels are.at ride height (2 post will have the suspension drooping)

Remember what I said in my PM. The trans angle and the pinion angle need to be the SAME but opposite angles. IE: if pinion is infact down 3 degrees, that would be -3* trans needs to be up 3*

What is the trans angle? "Flat" isn't a measurement.
Click to expand...
^^^^this right here!!!
 
drive-line-angle-jpg.jpg


This is what it should look like. The angle isn't hugely important, but they need to be equal and parallel as shown.

The rear might twist up 1-2 degrees at cruise too, so slightly nose down at rest is OK, but it can't "break across zero" (meaning the angle between the shaft and the pinion cannot go across 0 degrees, or -1 to +2 for example), and you never want the pinion and driveshaft in a straight line either.
 
str12-340 said:
I found a rubber insert bushing. Moving the trans down would make the mismatch worse and I can't move it up for reasons that I am very sure you understand.
Click to expand...

I don't think you're understanding.

If you're able to move the trans down 2* let's say. And move the pinion up 3-4* (with a shim) you're there.

Trans down (-2*) Pinion up (2*) those two angles are the same but opposite making them parallel.
 
Phreakish said:
View attachment 1716046775

This is what it should look like. The angle isn't hugely important, but they need to be equal and parallel as shown.

The rear might twist up 1-2 degrees at cruise too, so slightly nose down at rest is OK, but it can't "break across zero" (meaning the angle between the shaft and the pinion cannot go across 0 degrees, or -1 to +2 for example), and you never want the pinion and driveshaft in a straight line either.
Click to expand...
While I agree in theory with that graphic, it's wrong, wrong, WRONG for any type of performance application. The Mopar Performance manual has the dead best explanations and graphics for both street and race.
 
Here is a good article from QA1 about it. As with everything, it's totally dependent on WHAT you're doing with the car. The object is to shoot for the optimum drive line angle while under acceleration for performance cars. Pay attention to the last paragraph regarding racing. No, of course street cars don't need that strong an angle, but they also need more than what setting the angle "equally" at rest gives. As I said, the MP manual explains it perfectly. I wish like hell they'd not stopped printing those.

QA1
 
The angle should be measured on the damper at the crank centerline
 
fishmens67 said:
The angle should be measured on the damper at the crank centerline
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I don't know of anyone that does it like that, but that's actually probably the best place.
 
RustyRatRod said:
I don't know of anyone that does it like that, but that's actually probably the best place.
Click to expand...
It's a good place to measure up/down and side angle. I do it every time I install an engine.
 
RustyRatRod said:
While I agree in theory with that graphic, it's wrong, wrong, WRONG for any type of performance application. The Mopar Performance manual has the dead best explanations and graphics for both street and race.
Click to expand...

Agreed, but OP said 'not a race car' he wants smooth cruising only.
 
Phreakish said:
Agreed, but OP said 'not a race car' he wants smooth cruising only.
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I get it. My point was that he "probably" needs something somewhere in between granny's church goer and a prostock. I've never in my life set drive line angles at rest......well......you have to, but you understand what I'm saying. You have to guesstimate based on acceleration. Setting it at rest will result in a negative drive line angle under acceleration and that's a sure fire way to get a vibration.
 
RustyRatRod said:
I get it. My point was that he "probably" needs something somewhere in between granny's church goer and a prostock. I've never in my life set drive line angles at rest......well......you have to, but you understand what I'm saying. You have to guesstimate based on acceleration. Setting it at rest will result in a negative drive line angle under acceleration and that's a sure fire way to get a vibration.
Click to expand...

Yup, it's trial and error at best once parts start getting swapped. I run non-stock leaf springs and have a 3.91 rear end, so it takes an extra 3 degrees down from theoretical 'right' to run smooth uphill. Then I added assassin bars, and had to reset once again LOL.
I think it's more important for people to understand why the angle across the joint needs to be equal in the first place, helps visualize what's going on. In this day and age, I think folks would benefit from trying to stick a camera or phone under the car to take a video of the axle wrap during a quick drive. With some creativity, it could be used to really dial-in what's required.
 
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