Bad vibrations (Part 2!)

[5.7 hemi]

Right on! We are here to help.

 

[Dave145]

I certainly appreciate it! I never knew pinion angle was such a critical adjustment. I guess for shits and giggles I can try a 3 or 4 degree spacer block and see what happens next, because I wont have to remove the center pin from the spring pack. Plus if that amount doesn't work, it'll give me room to go up a few degrees.

I run the car with the rear end raised ~2-3" higher than stock by using the air shocks. Kinda got tired of the "it's a grandpa car" comments and I kinda like the way it looks.

 

[Paul_G]

OP, I dont know how you got under the car to check things out, but I had to get my cars suspension sitting on 4 jack stands to get myself under there. You want accurate measurements. Use a hardware store angle finder or there are phone apps for measuring angles too. You can use a large socket on the universal joint cup to place the angle finder against, or right on the yoke if there is room. You might need to raise or lower the trans, to get the angles right.

 

[Dave145]

Guys, slow down here a little. There is incorrect information being passed out. The link above is very important. The angle of the transmission yoke and the angle of the pinion yoke only have relation to each other, not the ground. The pinion yoke does not point down in relation to the ground. The picture of the differential above means nothing in relation to the ground. The pinion will never point down in relation to the ground.

With relation to the ground the transmission yoke will point down in most cases, about 4 degrees, the pinion yoke will point up in most cases usually about the same amount, 4 degrees. The two yokes must be at an equal but opposite angle to each other. Trans pointing down, pinion pointing up, both by the same amount but opposite. Because the trans is generally higher in the chassis than the rear axle, the drive shaft then will have a natural pitch down toward the rear axle. The angle between the drive shaft and both of the yokes must also be considered. Keep it under 2 degrees.

Because leaf springs will wrap, drag racers like to have the pinion a few additional degrees down in relation to the trans yoke. When the springs wrap up under power the pinion will naturally rise and correct to the desired angle, which will make the two angles equal but opposite, and only under full load, a drag car. A street car is different than a drag car. Because the springs will naturally wrap somewhat, it can be wise to give the pinion an extra couple of degrees down in relation to the trans yoke, but no more than that.

So does my setup sound correct to you? If not, what would you do different?

 

[Dave145]

I was able to wriggle under there and use an angle finer app on my phone to get the measurements.

 

[Paul_G]

Your pretty close if your numbers are right. 1 degree is very close, and the picture of the pinion and drive shaft looks like there is very little angle. If you wanted to try a shim I would not go more than 2 degrees down with the axle.

If the springs are very soft the axle could wrap throwing off the angles. But unlikely really. Can you get back under there and double check those angles? And get a picture of the trans mount? Is it centered in the housing, or pulled left or right?

 

[Dave145]

The trans mount is pulled more to the side. Which side exactly I don't recall at the moment. I rechecked all the angles tonight and they are still identical to the ones I posted earlier.

Driveshaft 2.4 degrees UP
Trans 4.2 degrees DOWN
Pinion Flange 3.5 degrees UP

 

[Paul_G]

The - and + angles are very difficult to get straight. To keep it simple, the trans should point down to the axle, and the axle should point up toward the trans. Unless you have a slammed hoopty or something. If the car is sitting on a sloped floor, the angles only have relation to each other, you must keep that in mind.

 

[Dave145]

That is what it looks like down there. They point at each other and are fairly close in values.

 

[Paul_G]

Two things

The left right angle is off a little if the trans mount is not centered. The trans mount can float left to right. The engine mounts determine where the trans mount will lay.

Trans 4.2 down with pinion 3.5 up. As the pinion climbs it will align itself closer to the 4.2 of the trans. Shimming wont fix this.

 

[Dave145]

Then what will? I guess I'm lost as to what the actual problem is here. Some folks say my measurements are bad and need shims to bring it down, you and others say that my measurements are fine and that there's another issue I'm not seeing.

 

[Paul_G]

Then what will? I guess I'm lost as to what the actual problem is here. Some folks say my measurements are bad and need shims to bring it down, you and others say that my measurements are fine and that there's another issue I'm not seeing.

Welcome to the internet! Take everything with a grain of salt.

I went back and did a reread of this 5 page thread looking for your engine and trans mounts answer. They are original? I would not stop now doing as much as you have already. Spend a few more bucks and change them out.

Also do a close inspection of the exhaust and drive line making sure there is nothing contacting the body that can cause the intermittent vibration you describe. You did say that sometimes it doesn't vibrate at all correct?

 

[Paul_G]

I am saying to change the mounts for this reason. I had a horrible vibration in my 72. It has a completely non original drive line. The trans mount was pulled way to the passenger side. All the axle shimming in the world didnt help. When I shimmed the engine mounts to get the trans mount to stay centered, the problem got noticeably better. There were many other issues as well, but getting the trans in the right place helped a ton.

 

[Dave145]

Sometimes it waits to vibrate till 75-80. But that is exceedingly rare.

The trans and motor mounts are original. I would have already replaced them, but the trans mount the last time I checked was $100 for a single mount. Hence where I decided to quit throwing away money and invest time into actually solving the issue.

The exhaust is mounted with rubber isolators on the hangars to keep its vibration from getting to the body. It ends just before the rear axle.

The driveline shows no signs of bodily impact, except for the fact that the pinion snubber is smushed and the axle bumpers (the rubber triangular pieces that mount to the body above the axle housing) are also smushed.

 

[miller]

Here is the pinion and driveshaft

That's your problem. At least part of it. U-joint straight in line, for what it's worth.

 

[747mopar]

I am saying to change the mounts for this reason. I had a horrible vibration in my 72. It has a completely non original drive line. The trans mount was pulled way to the passenger side. All the axle shimming in the world didnt help. When I shimmed the engine mounts to get the trans mount to stay centered, the problem got noticeably better. There were many other issues as well, but getting the trans in the right place helped a ton.

Welcome to the internet! Take everything with a grain of salt.

I went back and did a reread of this 5 page thread looking for your engine and trans mounts answer. They are original? I would not stop now doing as much as you have already. Spend a few more bucks and change them out.

Also do a close inspection of the exhaust and drive line making sure there is nothing contacting the body that can cause the intermittent vibration you describe. You did say that sometimes it doesn't vibrate at all correct?

I agree with everything your saying except he clearly says it driveshaft speed related (70 mph). Driveshaft rpm related vibrations are typically caused by the driveshaft, rear end or tires. Things touching the body or broken mounts (with the exception of the tranny mount) would be more noticeable when the driveline is moving the most not at 70 mph when everything should be smooth as silk.

Have you done any testing on the freeway yet? This is a simple tattle tail way to get your head wrapped around what's
going on. Run it up to 70 when it begins to vibrate then try hard acceration for a burst followed by letting off and letting it coast and take note of what it does. Mine being a standard makes it more noticeable in coast since I can just push the clutch in but you should still notice it. All your trying to do is make the pinion climb and drop so you can see where it gets worse.

 

[747mopar]

I agree with everything your saying except he clearly says it driveshaft speed related (70 mph). Driveshaft rpm related vibrations are typically caused by the driveshaft, rear end or tires. Things touching the body or broken mounts (with the exception of the tranny mount) would be more noticeable when the driveline is moving the most not at 70 mph when everything should be smooth as silk.

Have you done any testing on the freeway yet? This is a simple tattle tail way to get your head wrapped around what's
going on. Run it up to 70 when it begins to vibrate then try hard acceration for a burst followed by letting off and letting it coast and take note of what it does. Mine being a standard makes it more noticeable in coast since I can just push the clutch in but you should still notice it. All your trying to do is make the pinion climb and drop so you can see where it gets worse.

As for the grain of salt I can also agree but keep in mind my car did the exact same thing as the P.O. is describing and right at 70mph. I was playing with different gearing at the time as well and every gear swap resulted in the speed at which it vibrated changing accordingly so in my case it was a dead giveaway.

 

[Glenwood]

OP, I dont know how you got under the car to check things out, but I had to get my cars suspension sitting on 4 jack stands to get myself under there. You want accurate measurements. Use a hardware store angle finder or there are phone apps for measuring angles too. You can use a large socket on the universal joint cup to place the angle finder against, or right on the yoke if there is room. You might need to raise or lower the trans, to get the angles right.

I just went through this on the weekend when I moved the perches on my 64. I had the car sitting on dollies which was just enough room to squeeze my gut under and measure with an angle finder.

 

[Dave145]

I've driven it like this for over a year now. It sucks! It starts to shimmy at 65-70 and gets worse the faster you go. Accelerating/decelerating/coasting has zero effect on it.

After a lot more math last night, I believe I am in need of a 4° shim for the rear end.

 

[Sixpactogo]

I've driven it like this for over a year now. It sucks! It starts to shimmy at 65-70 and gets worse the faster you go. Accelerating/decelerating/coasting has zero effect on it.

After a lot more math last night, I believe I am in need of a 4° shim for the rear end.

I think you are about right with this scenario since your measurements seem to be real close to what you want in the end. I think if you had a ladder suspension with almost zero axle windup you would be within 1 degree. Since you have leaf springs, you end up with 4 or 5 degrees axle windup giving you a plus 3 or 4 degree angle if that makes any sense. My 68 Charger was doing the same thing as yours. High speed vibration. Here is a link to what fixed mine.
.http://www.quickperformance.com/Pinion-Angle-Measurement_ep_45.html