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Discussion Starter · #1 ·
My 66 Nova SS has had a high speed vibration since I bought it in Wisconsin and drove it home to Calgary about 15 years ago. I have since,rebuilt and balanced L79 engine,replaces clutch and pressure plate,replaced muncie with a superT10,replaced driveshaft and joints,replaved rear suspension springs with multi leaf,changed wheels and tires to 15" American Racing Mags. I still have the vibration in fourth gear at 3500 RPM. Does not vibrate in 3rd gear at 3500 RPM. I'm thinking I should replace my rear axles and bearing. What do you think?
BTW, my drive line angles are correct
 

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How's your alignment? Stock front end? Subframe tight? Bushings? Front wheel bearings? Drag link? steering box? Yoke on your pinion tight and no runout? Axle bearings could well be the culprit but... so many things that could be the issue... Shocks even, lower spring perch bolts, upper shock mount...
 

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Discussion Starter · #4 ·
How's your alignment? Stock front end? Subframe tight? Bushings? Front wheel bearings? Drag link? steering box? Yoke on your pinion tight and no runout? Axle bearings could well be the culprit but... so many things that could be the issue... Shocks even, lower spring perch bolts, upper shock mount...
Front end aligned when new wheels and tires installed,new input and output yokes on driveline.
My vibration shows up more in my seat and especially in my mirror.
I have airshocks and have raised and lowered rear to no avail
Have you checked the run-out at both ends of the installed driveshaft??

I've found factory rear pinion yokes out over .060" before, and would not be surprised to find front slip yokes out nearly as bad.
I had a new driveshaft built and replaced both yokes. That was my first guess
 

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When you are driving it down the road and the vibration starts, do you feel it more in the steering wheel or the 4-speed gear shift knob?

If it vibrates more in the steering wheel it points to being related to the front suspension or chassis.

If it vibrates more in the gear shift knob it points to the drivetrain.

Using a little deductive reasoning, from the limited amount of data provided it kind of points to the transmission.
I still have the vibration in fourth gear at 3500 RPM. Does not vibrate in 3rd gear at 3500 RPM.
If it was the engine, clutch/flywheel it would vibrate in 3rd gear too. So that means it is probably something further back.

Of the remaining components, which could cause the vibration at 3500 RPM in 4th gear only?

All of them, driveshaft, rear, tires are all spinning faster in 4th gear at 3,500 RPM than they are in 3rd gear at 3,500 RPM.

I would focus on the following in this order:
  1. Transmission
  2. Driveshaft
  3. Rear End
  4. Wheels & Tires
If it's the transmission you should be able to feel the vibration in your hand when grabbing the knob.
 

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Discussion Starter · #6 ·
When you are driving it down the road and the vibration starts, do you feel it more in the steering wheel or the 4-speed gear shift knob?

If it vibrates more in the steering wheel it points to being related to the front suspension or chassis.

If it vibrates more in the gear shift knob it points to the drivetrain.

Using a little deductive reasoning, from the limited amount of data provided it kind of points to the transmission.

If it was the engine, clutch/flywheel it would vibrate in 3rd gear too. So that means it is probably something further back.

Of the remaining components, which could cause the vibration at 3500 RPM in 4th gear only?

All of them, driveshaft, rear, tires are all spinning faster in 4th gear at 3,500 RPM than they are in 3rd gear at 3,500 RPM.

I would focus on the following in this order:
  1. Transmission
  2. Driveshaft
  3. Rear End
  4. Wheels & Tires
If it's the transmission you should be able to feel the vibration in your hand when grabbing the knob.
I feel it more in my bucket seat and of course I see my mirror start to vibe. I rehearing my tyranny with no change
 

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1969 Nova . . 2dr . . Chino Valley,Az USA
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Which kind of brakes - front & rear ?

Years ago some (alot) of drum brakes had weights on them ; just a thought . I would always mark any drums that I'd remove - so as to reinstall them the same .

Seems as if almost everything else has been checked - or replaced.

jim
 
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When it starts to vibrate at 3500 RPM in 4th gear what happens if you push in the clutch and disengage the drivetrain and coast at that speed? Is the vibration still there?

If not then its your drivetrain.

And after that if it only does it in 4th gear its either the transmission or the driveshaft (my guess would be transmission).
 

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It could be it, especially if you say you feel it more in the seat of your pants than the steering wheel or gear shift.

It's about the only thing left isn't it?

Did you replace the driveshaft?

I mean if it does it in 4th but not 3rd it has to be from the trans on back. Sounds like the only thing left out back is the rear.
 

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Poly or rubber engine mounts? Poly or rubber trans mount? I just changed out a Energy one polyurethane trans mount and put in a rubber mount and it's made quite a difference in felt vibrations. Also find a tire shop with a Hunter Roadforce balancing machine and check your wheels/tires. It has a roller that applies force to the tire so not only does it balance but also finds imperfections in the tires.
 

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Mike - 74 Nova Baltimore, MD
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... replaced driveshaft and joints
What was the diameter, length (u-joint center to center), tube thickness, and material of the driveshaft that was installed?

For example:
A 3 inch diameter, 52 inch long .083 thick chromoly driveshaft may experience a "half critical speed" vibration at 3600 rpm (see chart below).
Font Parallel Screenshot Number Slope
 
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