[goatwgn]

I know it may sound ridiculous, but a lot of people travel 80 mph on the Interstate around here. I have a weird vibration in my '66 Tempest Custom wagon. It has a GV overdrive behind the TH 400. I have a custom driveshaft from "The Driveshaft Shop" that has the CV up front, and the U joint in the back. No matter where I set the pinion angle, I have the same vibration. Engine was balanced when rebuilt back in 2011, by Mr. P Body. (455). Is definitely speed related because I can take it out of overdrive and put it back in it, and I get the same thing. It has a 1970 Oldsmobile Type O rear with 3.42 gears in an open axle. Brand new BFG radials all around on 15 inch Rally 2 wheels. I pulled the wheels and tires off another car, and installed them, same thing. Any experiences or ideas? I have a suspicion it may be the outer axle bearings, or runout on the rear axles. One of them has a tiny bit of play, but there are no leaks.

[Formulabruce]

This felt in steering, seat of pants, or its audible? How are your motor and trans mounts?

[goatwgn]

Originally Posted by Formulabruce

This felt in steering, seat of pants, or its audible? How are your motor and trans mounts?

Not really "audible". Feel it seat of pants, and mirror vibrates. The motor and trans mounts are all good.

[JLMounce]

You can try clocking the driveshaft 180 degrees from its current position. If it’s a tolerance stack between the engine, trans, driveshaft and rear gear, sometimes making that change will reduce or eliminate the issue.

As formulabruce mentioned, how is it being felt or heard?

It’s also very possible that the vibration or noise may be related to airflow around the car. Does rolling the windows up or down have an effect? Does the vibration increase, stay the same or reduce if speed is increased?

[goatwgn]

Originally Posted by JLMounce

You can try clocking the driveshaft 180 degrees from its current position. If it’s a tolerance stack between the engine, trans, driveshaft and rear gear, sometimes making that change will reduce or eliminate the issue.

As formulabruce mentioned, how is it being felt or heard?

It’s also very possible that the vibration or noise may be related to airflow around the car. Does rolling the windows up or down have an effect? Does the vibration increase, stay the same or reduce if speed is increased?

It doesn't make any difference if the windows are up or down. stays about the same if speed is increased. It may or may not go away at an even higher speed, but cant do that with the traffic around here. May need to find a track, lol

[steve25]

The rear U joint needs to be centered in the yoke very very well !
This is something I would check , in fact with a magnetic dial indicator if you have such .

[adynes]

Originally Posted by goatwgn

I have a custom driveshaft from "The Driveshaft Shop" that has the CV up front, and the U joint in the back. No matter where I set the pinion angle, I have the same vibration.

What pinion angles have you tried exactly? Have you tried running it directly inline with the driveshaft (as a diagnostic)? I don't know if it is appropriate to run 1 u-joint and 1 cv together. Two u-joints at equal but opposite angles will cancel the inherent rotational oscillation.

https://youtu.be/gmV4qwLfOMY

[goatwgn]

Originally Posted by steve25

The rear U joint needs to be centered in the yoke very very well !
This is something I would check , in fact with a magnetic dial indicator if you have such .

You may be on to something. I had a bent yoke on my Olds one time, and it caused a vibration. I had quite a bit of trouble installing this driveshaft onto the yoke. Very tight.

[Formulabruce]

I think your noise is the front pinion bearing. It already has a preload to the rear pinion bearing and is NOT supposed to have ANY front to back "thrust" on it during operation. With the GV, did all the play in a normal drive shaft input just vanish?

[Formulajones]

Nearly every one of these instances are related to driveline. Especially after overdrive swaps, gear vendors, modified or custom driveshafts and joints where the length and angles of things have been changed.

You didn't mention what you've tried for pinion angle or where you put the angle of the gear vendor install.

With the addition of the gear vendor, and extending the length of the output shaft, it's pretty critical to make sure you maintain a downward angle of the output shaft in the 2-4 degree area. More or less is probably getting on the excessive side. You may need to either shim or shave the mount or mounts to achieve this.

Then I'd concentrate on the rear pinion, shooting for the opposite of what you have up front. All this must be done at ride height.

Once you're there, if vibrations are still present, I'd be looking at the driveshaft assembly as a whole. Might have to try a new driveline shop, have it rebalanced or possibly completely start over with something custom made.

I'm willing to bet, something in that driveline is causing your issue.

[adynes]

Originally Posted by Formulajones

...it's pretty critical to make sure you maintain a downward angle of the output shaft in the 2-4 degree area. More or less is probably getting on the excessive side. You may need to either shim or shave the mount or mounts to achieve this.

Then I'd concentrate on the rear pinion, shooting for the opposite of what you have up front. All this must be done at ride height.

He has a CV/U-joint combo, so the equal+opposite operating angle does not work. I went to the Driveshaft Shop website and, as I suspected, they say the pinion angle needs to be inline (or very close) with the driveshaft to avoid inherent vibration with a CV/U-joint combo.

https://www.driveshaftshop.com/domes...-or-muscle-car

[lfdsteve]

Fwiw i had a similar issue and it turned out to be a bolt on my TKO making contact with the underside of the transmission tunnel when the shifter was in the overdrive position.
80mph? Meh, slow here in Michigan ��

[Formulajones]

I'd be ditching that setup for a real shaft setup properly. I see no need to run CV's in something adding more parts to what should be a simple deal. Especially when they have a clause right on their site that says "putting a cv joint where it's not needed will cause vibrations"

[Keith Seymore]

Originally Posted by adynes

What pinion angles have you tried exactly? Have you tried running it directly inline with the driveshaft (as a diagnostic)? I don't know if it is appropriate to run 1 u-joint and 1 cv together. Two u-joints at equal but opposite angles will cancel the inherent rotational oscillation.

https://youtu.be/gmV4qwLfOMY

This.

Originally Posted by adynes

He has a CV/U-joint combo, so the equal+opposite operating angle does not work. I went to the Driveshaft Shop website and, as I suspected, they say the pinion angle needs to be inline (or very close) with the driveshaft to avoid inherent vibration with a CV/U-joint combo.

https://www.driveshaftshop.com/domes...-or-muscle-car

This

Originally Posted by Formulajones

I'd be ditching that setup for a real shaft setup properly. I see no need to run CV's in something adding more parts to what should be a simple deal. Especially when they have a clause right on their site that says "putting a cv joint where it's not needed will cause vibrations"

This.

You need an even number of single cardon U joints in order for the accelerations to cancel out.

It will never work with one single cardon U joint unless that working angle is held perfectly straight.

K

[goatwgn]

Originally Posted by adynes

What pinion angles have you tried exactly? Have you tried running it directly inline with the driveshaft (as a diagnostic)? I don't know if it is appropriate to run 1 u-joint and 1 cv together. Two u-joints at equal but opposite angles will cancel the inherent rotational oscillation.

https://youtu.be/gmV4qwLfOMY

It doesn't seem to be an angle problem. I set it at 0, 1 and 2 degrees, no difference. I ran it on jackstands with no tires and brake drums on it, same thing. I ran it up to 120, gradually. then easily let off so it would gradually slow back down. the vibration disappeared over 90. when I rotated the driveshaft 180 degrees, it moved from 80-90, down to 70-80. So I believe it may be a balance issue with the shaft. 50-50 hindsight, I should have went with a 4l80e to get overdrive, but I am already in it for this now, so I am working with what I got. The GV unit output shaft is down slightly, almost level with the rear end. Been running it that way for 9 years with an aluminum shaft from Denny's, that was ok, but still had a little driveline vibration.

[steve25]

If you want to easily play with confirming / playing with the balance then get two or 3 radiator hose clamps that are big enough to fit on the driveshaft and you can slip them on 8 to 12” from the rear and then do your jack the car up deal again and see if you can get the vibration out and the balance better.

[johnta1]

What is the angle of the transmission?
What is the angle of the driveshaft?
What is the angle of the rear end?

Without knowing these there is no way to know what the 'pinion angle' should be?

You could be way off and 1,2,3 degrees is nothing?

With the CV joint, it would have to be straight as an arrow from tranny output shaft to the pinion gear center of the shaft.

[goatwgn]

The driveshaft is at .7 facing upward from the Gear Vendor unit. The rear end is at the same. Contacted The Driveshaft Sop. They are taking back the shaft to recheck the balance.

[Formulabruce]

Angle? If one has to pry the Driveshaft into place, there is Wayyyyyy too much pressure on the GV unit output, AND the Pinion.. Lets start there....

[goatwgn]

I found it. Thanks for all the input guys. The place I had install my GV unit back in 2012, evidently did not have my pinion angle set right. I had got the angle pretty close, and then threw in my old driveshaft. Evidently, the new one got damaged in shipping, as it appears it may have a little dent near the back. Ran smoother than it has in years, up to any speed I dare go.