Do I have a pinion yoke runout problem?

[roger1]

I've been trying to chase down a drive line vibration issue on my '83 El Camino.

Feel it at high speed.
Comes in at 60 and is the worst at 80 and then smooths out faster than that.


New transmission yoke, new balanced driveshaft with new u-joints.
Rear is a GM 7.5 with factory 3.42 gears (out of a Camaro) and an Auburn posi.
The pinion yoke is the one that came with the El Camino from the factory. It was a 2.41 open the way it came.
U-joint angles are good. Rear of transmission is down 1.6 degrees and pinion yoke is up 1.6 degrees. Driveshaft angle 3.9 degrees which results in a 2.3 degree u-joint working angle.

Did this procedure this morning.

What do y'all think?

Dial indicator in center of u-joint cap and calibrated to zero:

Turned 90 degrees. .018 difference:

Turned another 90 degrees. Now opposite to the calibrated cap. .004 difference:

And another 90 degrees to the last spot. .009 difference to the calibrated cap and .009 less than the opposite cap:

 

[81cutlass]

Check the driveshaft itself and see what the runout is. Not that the U joint runout isnt a concern, but the actual shaft first.

 

[roger1]

Measuring about 3" back from the weld, I get a max .009 runout when turning 360 degrees. The and the points 0 point and +.009 line up directly to the driveshaft yoke where I read a .009 difference between those u-joint caps.

Btw, I just had this driveshaft made. It's a heavier wall and not a tapered shaft like the original. I had this made because I thought my old one was out of balance but the vibration was the same as it was after I installed this new one. The guy who made it assured me he would balance it perfectly.

 

[roger1]

Measured again about a foot from the front of the driveshaft. Appears to be a little less there at .006.

 

[airboatgreg]

Are you sure it is driveline?
What happens when you put in neutral at vibrating speeds?
Where do you feel it? Steering wheel. seat of pants, front end, rear end?
Have you revved up engine in neutral AND park at the RPM that it is vibrating at?
Let me know

 

[roger1]

Are you sure it is driveline?
What happens when you put in neutral at vibrating speeds?
Where do you feel it? Steering wheel. seat of pants, front end, rear end?
Have you revved up engine in neutral AND park at the RPM that it is vibrating at?
Let me know

No question it's driveline. Does not vibrate at all revving it up in park.

You feel it in the seat of pants. About 2000 RPM at 60, 2400 at 70 and 2700 at 80. Dropping 4L60e out of OD increases rpm but vibrations are at the same vehicle speeds.
Smooth up to 60. Starts out a little cyclical, kind of an in and out vibration. Then gets a little worse going up to 70 and 75 and turns into a solid vibration (not cyclical anymore) at 80. It feels the worst there. Going up from 80 it smooths out. 90 is as fast as I've taken it in my test drives.
It's the same under acceleration, deceleration and steady. If I bump it into neutral at 80, the vibration is still there until it slows down to 60 where its totally gone.
I've raised the car on jack stands, removed the rear tires and put the lug nuts back on to hold the rear drums on tightly. When I run the car while watching the speedometer, it vibrates at the same speeds.

 

[airboatgreg]

If I bump it into neutral at 80, the vibration is still there until it slows down to 60 where its totally gone.

That is interesting...
Mark, then pull driveshaft. Make sure both u-joints are nice and free. Move them to max ranges. If OK put drive shaft back in but 180 degrees from your mark and see if any change. Look at transmission mount to confirm that it has not collapsed

 

[roger1]

I tried that already with the old drive shaft before I bought the new one. No change.
Since the new drive shaft didn't solve the issue, I think the test was valid with it.

Transmission mount is a Energy Suspension urethane mount. I tried a brand new stock type mount in it too. No difference there either.

 

[pagrunt]

Is the poly mount altering the angle? The ES 3.1108G mount does seem taller with the required plate between the mount & trans. I picked up a 3.1158G (shorter mount) to see what it would do to the drive line angle & looks like a 5 deg less change with out the body on the frame.

 

[roger1]

Is the poly mount altering the angle? The ES 3.1108G mount does seem taller with the required plate between the mount & trans. I picked up a 3.1158G (shorter mount) to see what it would do to the drive line angle & looks like a 5 deg less change with out the body on the frame.

Yes, the polyurethane mount is a different height than the stock mount. But, I have an aftermarket crossmember and it's set up for a urethane mount and the mount mounting surface is lower than the stock crossmember. I went to the aftermarket crossmember in order to install my dual exhaust system. With this crossmember and urethane mount, I still had to shim it up some to achieve the 1.6 degree down angle to match the 1.6 degree up I have on the pinion. I don't have adjustable rear control arms so I can't adjust the pinion angle at the rear. I have to do that at the transmission mount. I have air bags in the rear and 10 lbs in them gives me the ride height I like. At that ride height and the body approximately level, the up angle at the pinion is 1.6 degrees.