Shudder at 93 MPH...
Thread Starter
Joined: Jul 2014
Posts: 10,450
Likes: 1,873
From: My own internal universe
I still agree it doesn't seem to be the tires, but I arrived at the conclusion a different way --
I rotated the tires several times trying to even change the vibes to no avail. I even swapped out my wheels with someone else's who didn't have any issues, and it didn't help
I calculated that at 60 mph (1 mile per minute, 88 ft per second), the tire (305x30x19) is rotating exactly 18 rotations per second. This vibration feels faster than that. My gear ratio is 3.42, which means the DS is vibrating at 61.5 Hz. I can almost hear a low hum when it does it softly. When it gets violent, the other noises are louder, so I can't hear it anymore.
Now, if it's both, then all bets are off
I rotated the tires several times trying to even change the vibes to no avail. I even swapped out my wheels with someone else's who didn't have any issues, and it didn't help
I calculated that at 60 mph (1 mile per minute, 88 ft per second), the tire (305x30x19) is rotating exactly 18 rotations per second. This vibration feels faster than that. My gear ratio is 3.42, which means the DS is vibrating at 61.5 Hz. I can almost hear a low hum when it does it softly. When it gets violent, the other noises are louder, so I can't hear it anymore.
Now, if it's both, then all bets are off
Thread Starter
Joined: Jul 2014
Posts: 10,450
Likes: 1,873
From: My own internal universe
Thread Starter
Joined: Jul 2014
Posts: 10,450
Likes: 1,873
From: My own internal universe
Ok, progress!
Replaced front u joint. During the process, that round donut, damper looking thing - I almost took it off to see if it was part of it, but left it on at the last second. First, I put the slip yoke back in the trans and ran the engine and trans with the slip yoke in. No vibrations. When I pulled the slip yoke back out, the fluid on the yoke was all nasty, so now I'm nervous about the trans.
Reinstalled driveshaft and ran with wheels up all the way to 140 in 6th with no vibrations and wheels on the axle. I held cruising speeds at 70 - 100 for a bit and still smooth.
Wheels down and road tested. No vibrations until 80, and it feels like the front wheels - worst in the steering wheel. That gut shaking vibration from the center of the car is gone. At 90, the front settles back down, but the rear shakes. Definitely at the back.
So, now I'm thinking soft or hard spots in the tires is the next bogey to chase. That means match mounting and road force balancing I guess.
At least now I can drive a reasonable speed without the car shaking. Now aiming for driving at UNreasonable speeds
Replaced front u joint. During the process, that round donut, damper looking thing - I almost took it off to see if it was part of it, but left it on at the last second. First, I put the slip yoke back in the trans and ran the engine and trans with the slip yoke in. No vibrations. When I pulled the slip yoke back out, the fluid on the yoke was all nasty, so now I'm nervous about the trans.
Reinstalled driveshaft and ran with wheels up all the way to 140 in 6th with no vibrations and wheels on the axle. I held cruising speeds at 70 - 100 for a bit and still smooth.
Wheels down and road tested. No vibrations until 80, and it feels like the front wheels - worst in the steering wheel. That gut shaking vibration from the center of the car is gone. At 90, the front settles back down, but the rear shakes. Definitely at the back.
So, now I'm thinking soft or hard spots in the tires is the next bogey to chase. That means match mounting and road force balancing I guess.
At least now I can drive a reasonable speed without the car shaking. Now aiming for driving at UNreasonable speeds
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Joined: Nov 2014
Posts: 47
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Ok, progress!
Replaced front u joint. During the process, that round donut, damper looking thing - I almost took it off to see if it was part of it, but left it on at the last second. First, I put the slip yoke back in the trans and ran the engine and trans with the slip yoke in. No vibrations. When I pulled the slip yoke back out, the fluid on the yoke was all nasty, so now I'm nervous about the trans.
Reinstalled driveshaft and ran with wheels up all the way to 140 in 6th with no vibrations and wheels on the axle. I held cruising speeds at 70 - 100 for a bit and still smooth. Good work!, Now I need to solve my vibration issue.
Wheels down and road tested. No vibrations until 80, and it feels like the front wheels - worst in the steering wheel. That gut shaking vibration from the center of the car is gone. At 90, the front settles back down, but the rear shakes. Definitely at the back.
So, now I'm thinking soft or hard spots in the tires is the next bogey to chase. That means match mounting and road force balancing I guess.
At least now I can drive a reasonable speed without the car shaking. Now aiming for driving at UNreasonable speeds
Replaced front u joint. During the process, that round donut, damper looking thing - I almost took it off to see if it was part of it, but left it on at the last second. First, I put the slip yoke back in the trans and ran the engine and trans with the slip yoke in. No vibrations. When I pulled the slip yoke back out, the fluid on the yoke was all nasty, so now I'm nervous about the trans.
Reinstalled driveshaft and ran with wheels up all the way to 140 in 6th with no vibrations and wheels on the axle. I held cruising speeds at 70 - 100 for a bit and still smooth. Good work!, Now I need to solve my vibration issue.
Wheels down and road tested. No vibrations until 80, and it feels like the front wheels - worst in the steering wheel. That gut shaking vibration from the center of the car is gone. At 90, the front settles back down, but the rear shakes. Definitely at the back.
So, now I'm thinking soft or hard spots in the tires is the next bogey to chase. That means match mounting and road force balancing I guess.
At least now I can drive a reasonable speed without the car shaking. Now aiming for driving at UNreasonable speeds
Thread Starter
Joined: Jul 2014
Posts: 10,450
Likes: 1,873
From: My own internal universe
I meant to post this as well last night, but I re-verified my pinion angles. The angle finder I was using before only rounded to the nearest degree, so I got an iphone app that will read to decimal degrees.
Transmission down angle 4.3 degrees toward the rear. Pinion angle 3.8 degrees up toward the front. Driveshaft 0.8 degrees down from trans to pinon.
Going back to older posts by others who have fixed theirs, I see this is similar in terms of relative angles:
And finally, what I found to be the best advice on pinon angles at all...
I had my relative angles at zero, and after chasing them all over again, ended up back within a half degree of zero. Bottom line, if your pinion angles are zero and you have a driveline vibration while coasting - in or out of gear - start looking for worn or binding parts.
Transmission down angle 4.3 degrees toward the rear. Pinion angle 3.8 degrees up toward the front. Driveshaft 0.8 degrees down from trans to pinon.
Going back to older posts by others who have fixed theirs, I see this is similar in terms of relative angles:
Originally Posted by ThoR294
I assume that is why when I cranked the rear down (it was pointing down almost 3degrees), the vibration wasn't too bad, but it wasn't perfect. Now that I did the 3degree down for trans and 2.65-2.75 up for rear... its perfect
Originally Posted by Hiltsy855
I ended up adding a 1/4" shim under the trans mount and raising pinion until the trans and pinion are parallel. Now I have no vibrations at highway speeds and the car is much more enjoyable to drive.
Originally Posted by 01Reda4SS
Pinion angle at zero gives the least vibration. Period. The thought of setting it at -2 is so under load when the rear squats and the pinion pushes up one or two degrees you are at exactly zero under the highest driveline load which is the least painful to ujoints for one. As the rear squats, the pinion angle goes positive by a degree or two. I'm thinking you may be slightly confused in your terminology and methods to checking pinion angle and think you should do more research on the matter. I too had vibrations after doing a relo bracket. Turned out I was at positive 3 or so. I took it to zero and it went away. I took it to -1 or so for the long haul and the vibe is still basically gone.
Originally Posted by 01Reda4SS
All the confusion aside, make your joint angles even, like dead nuts the same. I had the same vibe with a BMR torque arm cross member. Turns out my pinion angle was ****** as soon as I put it on. My trans was down 3 degrees, so I matched my rear by aiming it up 3 degrees and everything is smooth. My vibes came in at about 80-90 just like yours. Simplest way to explain it is whatever your trans tail angle (measure from the front u joint) is, make the rear end match by adjusting the torque arm. Make them the exact same, if the angle gauge says 6 on one, make the other read identical.
