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This thread is really putting things together for me ... things that I sort of knew are starting to make sense.

About the parallel thing: If you don't have parallel ins and outs, the phasing might be correct at 12 oclock and 3 oclock positions, but with other positions showing early and late phase positions. So there would be a hurry up and slow down effect on the output compared to the input speeds. I think that would cause vibration.
o_O
 
Discussion starter · #22 ·
Here's a little experiment I cooked up and tried myself that you can use to understand exactly why having the two centerlines parallel with each other in 3D space matters.
I used a cordless screwdriver, a couple of socket u-joints, and a couple extensions.

Start with just one extension. Like this:
View attachment 165289

Hold the end in your hand, turn on the screwdriver. You'll feel a vibration. More more the angle, the more you'll feel it. This is because the end extension is not turning at a constant speed. It's actually speeding up and slowing down slightly with each revolution due to the action of the ujoint. There's a mathematical geometrical explanation as to why this happens, but it's a lot more powerful to experience it actually happening with your own senses.

Now add another extension and another ujoint.

View attachment 165283

Hold the end extension in your hand and turn on the screwdriver. If you try changing the angle on the end extension, you'll be able to find an orientation where, even though the middle extension is still "at an angle" to the other two and is still "speeding up/slowing down" with every revolution, the rotation feels smooth and constant in your hand because the reverse angle "cancels out" that "speeding up/slowing down" that the ujoint imparts to the middle extension. This parallel alignment is what you must achieve between your trans/crank centerline and your pinion centerline in order to get rid of the vibration. It doesn't matter which "direction" the two lines aren't parallel (vertical, horizontal, etc) - they have to be parallel in all directions. That means that if you "square" your rear axle to the frame, but the engine/trans is NOT "square" to the frame, you're still going to get a vibration even if the "up/down" angles are perfect.

Try it. It actually works.

This is why you feel a vibration if the trans/crank centerline is out of alignment with the pinion centerline.

Bear
Good stuff and I think they used that same tool for my colonoscopy 😉 I don’t have anymore vibration than I have in the past, I've always had some through the shifter handle but I thought it was from the steel bushings.
 
Discussion starter · #23 ·
Thinking about this some more my questions are if someone like me has only adjustable upper arms when I try and square the pinion with the engine/trans horizontally won't I be changing the vertical angle also? And then what about most of the cars that have no adjustable arms, they just have to hope for the best? I've heard of getting the rear end centered side to side and straight with the frame front to back but never parallel with the trans output shaft. So if I want to check if the rear end is square with the frame and I have a laser ruler where are the best places to measure? Last question, which is the lesser of to evils to have off the vertical pinion angle or horizontal? I'll hang up and listen for my answers, thanks.
 
Yes, it will change both --- so it's not difficult to get into a situation where you have to measure and make adjustments to both multiple times to get things lined up in both planes.

Yeah, if you don't have adjustable rear arms, you just have to "get lucky" which usually means all the control arms, transmission mounts, motor mounts, crossmember(s), etc. have to be dead stock, and hope you don't have "frame spread" in the front.

As far as making the measurements, you just have understand the relationships you're trying to achieve and then figure out a way that works for you with the tools you have, or the ones you're willing to procure, and be as meticulous about it as you can.
Neither plane is more important than the other. Think about it - using the screwdriver "experiment" I described. Say for example the horizontal is perfect but the vertical is off. Turn the whole contraption, without changing any of the angles, exactly 90 degrees. Now the vertical is perfect, but the horizontal is off --- and it's still going to vibrate just as much.

Bear
 
Discussion starter · #25 ·
Yes, it will change both --- so it's not difficult to get into a situation where you have to measure and make adjustments to both multiple times to get things lined up in both planes.

Yeah, if you don't have adjustable rear arms, you just have to "get lucky" which usually means all the control arms, transmission mounts, motor mounts, crossmember(s), etc. have to be dead stock, and hope you don't have "frame spread" in the front.

As far as making the measurements, you just have understand the relationships you're trying to achieve and then figure out a way that works for you with the tools you have, or the ones you're willing to procure, and be as meticulous about it as you can.
Neither plane is more important than the other. Think about it - using the screwdriver "experiment" I described. Say for example the horizontal is perfect but the vertical is off. Turn the whole contraption, without changing any of the angles, exactly 90 degrees. Now the vertical is perfect, but the horizontal is off --- and it's still going to vibrate just as much.

Bear
Gotha, it's just funny because you hear about vertical pinion angle all the time but I wonder how many people especially here have heard of horizontal angle, I bet not many so that made me think it isn't as important and after reading about how many cars came stock with offsets of 2 inches or more I guess I wasn't to concerned but I probably should look into it, thanks.
 
Discussion starter · #26 ·
Well the best I can come up with is the crank is 3.15° down the diff or pinion is 2.35° down and the shaft is 1.65° down.
 
Discussion starter · #27 ·
Forgot to average the crank pulley, after 180° it's 3.05° so 3.10°, I didn't remove the driveshaft so I took reading on the face of the diff where the seal goes into like they showed on the video, the seal does not cover the face and I took a reading on top of the case where the pinion comes out. My angle finder has a groove and magnet, at 2.35° it's more than I was measuring on the flat of the yoke, that was 1.40° so idk maybe I'll have to pull the shaft. But if the 1.40° is right I'm way off, the 2.35° is closer. I do have a shim for the trans mount that the guy doing the alignment took out when he saw the drag link rubbing the pan but it didn't help so I installed 1/4" mount spacers, maybe I should put the shim back in or should I adjust the diff down to 3.10° ? The trans spacer is an 1/8".
 
Discussion starter · #28 ·
Also I did some measuring with my laser tool at four different points, lower control arm front mounting bolts to the same spots on the rear end, a couple places on the frame and on the cross member. Three measurements came within an 1/8" and one a 1/16" so if that's a good method them I'm pretty darn square in the frame.
 
Also I did some measuring with my laser tool at four different points, lower control arm front mounting bolts to the same spots on the rear end, a couple places on the frame and on the cross member. Three measurements came within an 1/8" and one a 1/16" so if that's a good method them I'm pretty darn square in the frame.
I used to do four wheel alignments on cars all the time, even with solid axle rear end cars and trucks to verify that there was no 'thrust angle', which would indicate a cocked rear end or bent rear axle tube. Which would result in a pull to one side or the other no matter how dead-nuts the front wheels were aligned. Built in 'rear steer'! The only vehicles that had significant issues with a thrust angle were those that had been really wrecked hard and not repaired properly, or those with a bent rear axle housing tube.
The factory control arms and mounts on these old A body cars were usually dead nuts on even when they were decades old. Unless the bushings were shot or one of the arms was bent from being jacked up with a floor jack. So what I'm saying is that MOST of these rear ends on a non-damaged car were square and straight.
 
Discussion starter · #30 ·
Ok BearGFR or whoever I reinstalled the trans shim and I'm coming up with an average of 2.95° down slope on the crank, trans yoke average of both sides 2.90° down of course and the diff cover bolts .090 pinion down (which is an acceptable point to measure according to Strange) also jives with the casting on the cover, drivshaft is showing 1.90° down from the trans. So from what you said to get the pinion and trans output shaft parallel I have to nose down the pinion 2.00° so it comes out to 2.90° correct ? Then if the shaft is at 1.90° I would have 1.00° negative which should be good on the street correct?
 
Discussion starter · #31 ·
....according to your diagrams I might have said it backwards, the pinion needs to point up 2.90° to be parallel to the motor pointing down 2.90° is that correct? And I put the shim back in because the video you posted said no more than 3.00° down angle of the motor so before I was 3.10°.
 
....according to your diagrams I might have said it backwards, the pinion needs to point up 2.90° to be parallel to the motor pointing down 2.90° is that correct? And I put the shim back in because the video you posted said no more than 3.00° down angle of the motor so before I was 3.10°.
Below is the 1965 AMA engine angle spec for 1965 Tempest and Lemans as I already pointed out. Not sure where the "no more than 3 degrees down" comes from (believe that is for Chevelle, but seems the factory did not have an issue with more than 4 degrees down and no vibrations.

I don't think the engine down angle should have a lot of bearing per say, rather it should be the balancing out of the two angles, engine & pinion. How do those up in the sky 4-wheelers do it with their radical driveshaft angles?

If your crank centerline and pinion angles are equal but opposite each other you shouldn't have driveline vibration - in theory. However, the minute you accelerate, the pinion will raise up and the angle up will increase and you may experience vibration.

So get the angles to cancel each other (neutral), then drop the pinion angle down 2 degrees and take it for a drive. If you have any vibration, then try 1 degree down from neutral. Does it improve or get worse. Make these changes from your base line of the angles cancelling each other out and simply test drive it. Measurements must be done at ride height/suspension loaded.

I found this explanation of the engine/pinion angles and you also want to include the driveshaft angle itself. So it can be more than just engine/pinion angles cancelling each other out. Maybe this will help.

The yokes at the trans come in different lengths. I read that one Chevelle guy switched the long yoke length for the shorter yoke length and that improved the vibration if you experience anything- but this would change your driveshaft length.

So just set the angles to cancel each other out, drop the pinion angle down 2 degrees, and test drive. Then adjust as necessary and road test. Each car will be different and pinion angles can be different for different driveline combinations, so 1 size may not fit all.

(y)


Font Rectangle Symmetry Monochrome photography Pattern


Font Parallel Auto part Engineering Motor vehicle
 
Discussion starter · #33 ·
Below is the 1965 AMA engine angle spec for 1965 Tempest and Lemans as I already pointed out. Not sure where the "no more than 3 degrees down" comes from (believe that is for Chevelle, but seems the factory did not have an issue with more than 4 degrees down and no vibrations.

I don't think the engine down angle should have a lot of bearing per say, rather it should be the balancing out of the two angles, engine & pinion. How do those up in the sky 4-wheelers do it with their radical driveshaft angles?

If your crank centerline and pinion angles are equal but opposite each other you shouldn't have driveline vibration - in theory. However, the minute you accelerate, the pinion will raise up and the angle up will increase and you may experience vibration.

So get the angles to cancel each other (neutral), then drop the pinion angle down 2 degrees and take it for a drive. If you have any vibration, then try 1 degree down from neutral. Does it improve or get worse. Make these changes from your base line of the angles cancelling each other out and simply test drive it. Measurements must be done at ride height/suspension loaded.

I found this explanation of the engine/pinion angles and you also want to include the driveshaft angle itself. So it can be more than just engine/pinion angles cancelling each other out. Maybe this will help.

The yokes at the trans come in different lengths. I read that one Chevelle guy switched the long yoke length for the shorter yoke length and that improved the vibration if you experience anything- but this would change your driveshaft length.

So just set the angles to cancel each other out, drop the pinion angle down 2 degrees, and test drive. Then adjust as necessary and road test. Each car will be different and pinion angles can be different for different driveline combinations, so 1 size may not fit all.

(y)


View attachment 165437

View attachment 165447
So when you say cancel out each other are you meaning the trans tail shaft and the pinion being parallel so equal degrees just opposite, motor down pinion up? Then if I'm preloading the pinion down 1 or 2 degrees they're not going to be parallel right? That's how it's set now with the pinion pointing down .090° down. Am understanding that correctly? The only vibration I have which I've had for years is in the shifter but idk if it's from the steel bushings.
 
If your engine/trans is down 2.90 degrees and you want the 1.5 degree preload (halfway between 1 and 2), then your rear pinion should point up 1.4 degrees. 2.90 up pinion angle would be parallel to 2.90 down engine/trans angle. 2.90-1.5=1.4
Assuming your floor is basically flat the angle of the floor will have no effect because you are checking the angles relative to each other - this procedure has been done on ships and boats that aren’t level.
 
Discussion starter · #35 ·
If your engine/trans is down 2.90 degrees and you want the 1.5 degree preload (halfway between 1 and 2), then your rear pinion should point up 1.4 degrees. 2.90 up pinion angle would be parallel to 2.90 down engine/trans angle. 2.90-1.5=1.4
Assuming your floor is basically flat the angle of the floor will have no effect because you are checking the angles relative to each other - this procedure has been done on ships and boats that aren’t level.
That's what I was thinking I have adjust the pinion up, it's down .90 now and a little pre load I hope is ok but it won't be parallel like it's supposed to be or I make it parallel now and if I race it I'll put some preload into it.
 
My understanding is that preload is only needed for leaf spring cars, because under power springs flex and allow the axle housing to "wrap up" a little, and that mostly happens only under hard acceleration. That doesn't happen on cars with "4-link" upper/lower control arms that prevent axle wrap up. I suppose the factory rubber bushings in the rear might get "squished" a little under hard acceleration - maybe.
I'm willing to be further educated about that though...

Bear
 
Discussion starter · #38 ·
My understanding is that preload is only needed for leaf spring cars, because under power springs flex and allow the axle housing to "wrap up" a little, and that mostly happens only under hard acceleration. That doesn't happen on cars with "4-link" upper/lower control arms that prevent axle wrap up. I suppose the factory rubber bushings in the rear might get "squished" a little under hard acceleration - maybe.
I'm willing to be further educated about that though...

Bear
I think it is much less with a four link but still might have a little and even less on mine with poly bushings and roto joints, I think I complicated the situation by adjusting the angle with the car facing down hill in the garage and now I'm checking things with it facing up hill. I'm going to pull the pinion up parallel to the motor at 2.90* I think and see how it feels, that should give me 1.00* difference from the shaft to keep the needle bearings working....sound good ?
 
I think it is much less with a four link but still might have a little and even less on mine with poly bushings and roto joints, I think I complicated the situation by adjusting the angle with the car facing down hill in the garage and now I'm checking things with it facing up hill. I'm going to pull the pinion up parallel to the motor at 2.90* I think and see how it feels, that should give me 1.00* difference from the shaft to keep the needle bearings working....sound good ?
Start there, and then you can paly/road test by changing the pinion angle up/down .5 degrees at a time. The vibration may be normal from the shifter.

The pinion angle may be more important when you go back to the drag strip and really stand on it when you dimp the clutch. Pinion angle can affect traction.
 
Discussion starter · #40 ·
Ok an update....just adjusted the pinion up to 2.90° to match the motor, shaft is at 1.05° took it for a drive and didn't even get to 40mph and I get a bad vibration. Never felt anything when it was pointing down
.90° I get the same reading on both sides of the cover bolts with a straight edge and the casting in the cover. Either Strange is wrong or the car just doesn't like positive pinion angle, I'm dropping it down again 🤦‍♂️
 
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