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Driveline vib, driveline angle measurements inside, help!

Old 02-02-2019, 03:18 PM
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Driveline vib, driveline angle measurements inside, help!

I'm trying to track down a driveline vibration that occurs at highway speed, usually 65mph+ and gets worse as you go faster. I just checked all driveline angles with a magnetic angle finder and have the following info:

Transmission angle: 3.5 deg downward
Pinion angle: 1 deg upwards
Driveshaft angle: 1 deg sloping downward from trans to rear pinion.

I am running a 4l80e trans with holley crossmember and a poly mount. 4th gen rear with a brand new custom steel balanced driveshaft.

Do these angles look ok? The holley crossmember has adjustment in the torque arm that will change pinion angle if needed. Any help would be great!
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Old 02-02-2019, 04:13 PM
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Re: Driveline vib, driveline angle measurements inside, help!

No, not really OK...

Ideally you want the trans and the pinion at the same angle. I.e. if you drew a straight line through each, the lines would be parallel. Yours are not.

If you can raise the front end of the torque arm, that's the direction the pinion needs to go. About 2 or so. Maybe just a bit less, maybe, so that when engine torque does what it does, which is to raise the pinion slightly, they're parallel when powered.
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Old 02-02-2019, 11:04 PM
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Re: Driveline vib, driveline angle measurements inside, help!

Thanks! Will try to get it adjusted tomorrow. Could I also shim the trans bracket to reduce the downward angle to match the 1 deg upward angle of the pinion?? Just looking for a few options.
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Old 02-03-2019, 09:00 AM
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Re: Driveline vib, driveline angle measurements inside, help!

You could try that; I guess it would depend on how much tunnel clearance you have. I doubt it would be as effective as adjusting the rear's angle though. Try the correct, designed-in approach first.
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Old 02-03-2019, 09:17 AM
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Re: Driveline vib, driveline angle measurements inside, help!

Originally Posted by sofakingdom View Post
You could try that; I guess it would depend on how much tunnel clearance you have. I doubt it would be as effective as adjusting the rear's angle though. Try the correct, designed-in approach first.
will do! Will post results after I get it adjusted today
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Old 02-03-2019, 03:14 PM
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Re: Driveline vib, driveline angle measurements inside, help!

adjusted the mount to its max setting and ended up with the following angles:

Transmission angle: 3.5 deg downward
Pinion angle: 2 deg upwards

So i gained one degree by adjusting my torque arm mounting position on the crossmember. Took the car for a quick spin and it felt better, but will have to get some highway miles logged to really tell.

Getting an alignment tomorrow, may try to put some miles on after I get it back.
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Old 02-03-2019, 04:23 PM
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Re: Driveline vib, driveline angle measurements inside, help!

Originally Posted by sofakingdom View Post
No, not really OK...

Ideally you want the trans and the pinion at the same angle. I.e. if you drew a straight line through each, the lines would be parallel. Yours are not.

If you can raise the front end of the torque arm, that's the direction the pinion needs to go. About 2 or so. Maybe just a bit less, maybe, so that when engine torque does what it does, which is to raise the pinion slightly, they're parallel when powered.
Agreed. Make sure you are measuring against a true 0* off of 90*. I used the front engine pulley to get a measurement for the trans and the yoke on the rear. My torque arm mount is parallel to the pinion CL so that made it easy to measure with the drive shaft installed. My trans is angled at 6*, if I remember correctly. Regardless, on the trans and rear you have to get a good flat surface to make sure the measurements are accurate. Trans and rear should be the same or as sofa mentioned you can let the rear 1* or so lower than the trans so it rotates even under power. Also, keep the u-joint angles under 5* if possible. My trans is angled toward the ground, the driveshaft is almost level and the rear points up. If you have an adjustable torque arm it helps a lot.
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Old 02-03-2019, 05:41 PM
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Re: Driveline vib, driveline angle measurements inside, help!

[color=left=#000000]trans is angled toward the ground, the driveshaft is almost level and the rear points up[/color]
This is generally pretty close to the way it works out when everything is right.

All of that of course, with the car sitting on a level surface, with the suspension at normal ride height... doing this on ramps with somebody about your size sitting in the driver's seat, somebody else about your SO's size in the pass seat, and a full tank of gas, is a great way to get that part right.
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