Drivetrain Vibration Questions

[Twisted_Metal]

When it’s up on stands and you checking u-joints….
Check for rotational “play” AND end to end “play” in the pinion yoke.

It only takes a few thousandths of an inch of slop to set up a harmonic vibration at just the right RPM range.

The yoke on my car got slightly “splayed” during a u-joint change (DOH!) and I have that same type of vibration at around 65 MPH.

 

[Glava]

When it’s up on stands and you checking u-joints….
Check for rotational “play” AND end to end “play” in the pinion yoke.
It only takes a few thousandths of an inch of slop to set up a harmonic vibration at just the right RPM range.
The yoke on my car got slightly “splayed” during a u-joint change (DOH!) and I have that same type of vibration at around 65 MPH.

Thanks, I'll check these.
I have not done everything yet, but here is what I did on the weekend:
I put the Z on floor jacks -under the rear axle and under the lower "A" arms.
Brought the speed up to 70mph and 80mph -very little if any vibration.
I switched the front tires to the back - very little if any vibration.
Checked and retightened the front wheel bearings -since I had repacked them a couple of times, I agreed that maybe I didn't get them right.
I left the tires in the rotated positions and road tested and at 70 and 80, the vibration was the same as it had been.
I was thinking that this lack of vibration on the jack stands, with the tires before I did the rotation and after being rotated, may mean that it may not be tire balance?
I also wondered if the lack of vibration while on jack stands may have ruled out the driveshaft and the U joints, which feel tight?
If any of the above makes sense, would that point me towards my Kelsey replacement retro Goodyear Polysteel radials being out of round or having a belt problem?
That I'm not so sure of, because with the original Uniroyal tires that I took off I had this vibration -seems add that both sets of tires would create the same vibration.
So, to me, the last common denominator would be the rims? One was replaced, but I'm going to look it over good again and verify if it is bent or out of round.
The other odd thing is that one of the wheels on it now, which was road force balanced, seems to have quite a few weights on it, inside and outside lip, plus a stick on weight in the middle between the lips -seems odd?

 

[MChamp]

coulda been the dude balancing it ran out of a certain weight. I'd take it to someone else before dropping the dime on new tires. and check your pinion angles.

 

[biker]

Thanks, I'll check these.
I have not done everything yet, but here is what I did on the weekend:
I put the Z on floor jacks -under the rear axle and under the lower "A" arms.
Brought the speed up to 70mph and 80mph -very little if any vibration.
I switched the front tires to the back - very little if any vibration.
Checked and retightened the front wheel bearings -since I had repacked them a couple of times, I agreed that maybe I didn't get them right.
I left the tires in the rotated positions and road tested and at 70 and 80, the vibration was the same as it had been.
I was thinking that this lack of vibration on the jack stands, with the tires before I did the rotation and after being rotated, may mean that it may not be tire balance?
I also wondered if the lack of vibration while on jack stands may have ruled out the driveshaft and the U joints, which feel tight?
If any of the above makes sense, would that point me towards my Kelsey replacement retro Goodyear Polysteel radials being out of round or having a belt problem?
That I'm not so sure of, because with the original Uniroyal tires that I took off I had this vibration -seems add that both sets of tires would create the same vibration.
So, to me, the last common denominator would be the rims? One was replaced, but I'm going to look it over good again and verify if it is bent or out of round.
The other odd thing is that one of the wheels on it now, which was road force balanced, seems to have quite a few weights on it, inside and outside lip, plus a stick on weight in the middle between the lips -seems odd?

Lots of weight on a wheel is a red flag. Weight in two different places on one side means it was a poor balancing job.

 

[COPO]

I have minimal balance weights on my 70 Z28 rims with no vibrations at any speeds. I still remember in ‘75 while driving in my 71 Z28 with M22 the speed I started to get vibrations at 150 mph. And that is no sh!t.

 

[Glava]

Lots of weight on a wheel is a red flag. Weight in two different places on one side means it was a poor balancing job.

Thanks, I know that's what I thought, but I've had the original tires and newer tires balanced numerous times and it seems like they all do it that way?
When I was working at a full service gas station in high school, about 1973 -74, I bubble balanced hundreds of customer tires and would place the weight until the bubble was centered - I think that the only time I put a weight on the inside and outside was if it was a big weight, I may split the weight in half.
The new road force balancing seems to come up with odd weight patterns.

 

[Glava]

I have minimal balance weights on my 70 Z28 rims with no vibrations at any speeds. I still remember in ‘75 while driving in my 71 Z28 with M22 the speed I started to get vibrations at 150 mph. And that is no sh!t.

I know, before I brought the new tires to be installed, I had taken off all of the weights to be sure that they did it that way. OK, so my 175HP 350, Borg Warner T-10 Close ratio and 3.73 Posi tops out at about 120mph.....

 

[mallard]

Given the history, I think the OP can pretty much rule out wheels & tires. Further, if it's "seat of the pants" vibration then I see it as being drive shaft, ujoint or rear brake drum related. Regarding the "unusual" amount of wheel weights, one possible experiment is to rotate that tire on the wheel 180 degrees and rebalance it. While I doubt that's your problem, it's probably worth attempting to correct in any event.

 

[biker]

Thanks, I know that's what I thought, but I've had the original tires and newer tires balanced numerous times and it seems like they all do it that way?
When I was working at a full service gas station in high school, about 1973 -74, I bubble balanced hundreds of customer tires and would place the weight until the bubble was centered - I think that the only time I put a weight on the inside and outside was if it was a big weight, I may split the weight in half.
The new road force balancing seems to come up with odd weight patterns.

Understood. Wheels/tires seems like something you have beaten to death now. I agree with Mallard, it is something a bit deeper.

 

[Dave Nelson]

Don't know if this was addressed but have you checked the trans mount?