Just had the differential rebuilt on my 1975. New half shafts and new u Joints in the driveshaft and new balanced tires. I still have a slight vibration. Anyone have ideas on how to determine what the root cause is?

I had a vibration in my C3, but it was the steering pump.

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MICK - C3VR Lifetime Member #113

You've certainly covered most of the bases Jack. The rear wheel bearings would have to be pretty bad ( and easily checked) before causing vibration but heavily worn trailing arm bushings have been known to contribute.

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Jimmy B.
Just can't wait to get on the road again.

 
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Automatic or manual trans?
Heavy vibration, or light?
Is it steady, or does it seem to come and go?

Lot of things can cause vibrations, and you've replaced a lot of stuff back there. Did you have this vibration BEFORE doing any of this, or was this the reason you did all of the work?
Does the vib. feel like it's in the rear, front, or the center of the car?

The trans or engine mounts could be sagging/soft, could be a flywheel(manual)/torque converter(automatic) out of balance, harmonic balancer on the front of the engine....so many possibilities.

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Joel Adams
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It's a 4 speed manual. The vibration is 'slight'. I have been trying to see where it is the most noticeable. I can feel it on the shifter and also see the rear view mirror vibrate.

DUDE ! Go for it ! But try to keep it below 60,at least in the parade.

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Jimmy B.
Just can't wait to get on the road again.

 
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[QUOTE=jp75vette] It seems to be dependant on RPM as it comes in and out as I accelorate through the gears.[/QUOTE]


Good info...
Now...does it seem to only vib. when accelerating, as when the drivetrain is under a load, or can you get a vib. just sitting still, with the trans in neutral, at a certain rpm?
If you are driving at a steady speed, under power, with the vib., if you put it in neutral, does it go away?

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

The vibration seems to be worse while accerating and it seems to be worse at approx 1500 RPM. It also vibrates when I depress the clutch and rev the engine.

I think you may have a flywheel/clutch balance issue, OR...the pilot bushing in the crankshaft, for the trans input shaft, is worn, allowing the input shaft to run off-center, and create a vibration.

[QUOTE=jp75vette]One strange thing is that the vibration really gets worse when I decelerate with the clutch in gear.[/QUOTE]

Do you mean while you are driving at speed, and push in on the clutch, but leave the trans in gear? If so, then this would definitely point to a pilot bushing/input shaft problem...

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Joel Adams
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Yes that's what I did, why I'm not sure, but it really vibrated.

[QUOTE=jp75vette] Is the pilot with a bearing worth looking at?[/QUOTE]

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Jimmy B.
Just can't wait to get on the road again.

 
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The bearing styles are much better, in terms of less friction, and more precise location of the shaft, but they will do more damage to the input shaft once they take a dump.
Is it worth the trouble of changing from a bushing to a bearing? Not really...the bushings work really well, for a lot of miles, with no problems....as long as they are installed correctly...meaning NO GREASE OR OIL on them when installed.
The bronze pilot bushings are made with an oil impregnated(you heard me...) material, that needs NO lubrication. If you put a little dab(or a big blob) of grease on them, what that does is "cook" into the surface of the bushing, an essentially block the oil in the bushing from being released, which makes the bushing dry, which in turn wears it and the input shaft pilot out really quick.

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"