Just got the transmission rebuild on the conv which is great. But my mechanic tells me there is a vibration in the car when you rev the engine up? He thinks it might be the fan. I just replace the fan with a 7 blade. What could cause the vibration?

I assume this is the 70? Did you notice the vibration before the trans rebuild..is it auto or stick..if stick did they replace the clutch and or flywheel when doing so? If auto did they replace the torque converter? If neither apply then it could be anything that spins on the front of the motor..ie fan..harmonic balance rubber coming apart..bent pulleys..alt and ac issues..

Also if stick does it work right? No noises at idle and goes into first ok..it may have a bad input bearing or assembled wrong..or pilot bearing..need a little more info..
PS I have a vibration at high RPM when I am not moving I haven't got to yet..its on the list..I suspect the harmonic balance on mine..
Rich

Its the 70 conv and I just had the trans rebuild. No they did not replace the clutch or fly wheel. And I did notice a vibration before I thought it was the tanes going bad.

Well that makes a big difference...I was hoping for the best!  Well I guess if you put the fan on and then felt the vibration then thats the problem..if you put a spacer on it and removed the clutch fan it may be unbalanced..if you used a factory style one they are balance to a point..that's why the blades are spaced unevenly..the aftermarket ones use smaller blades to fit in the same diameter space..try pulling off the belts one at a time and see if the vibration goes away..if you have all the belts off and it still vibrates it could be the harmonic balance..it could also be the clutch and flywhell setup also..just easier to start up front..

here is a vibration check list to try and locate the problem. I have a vibration also at about 1200 RPM and also at 3500 RPM. I had a guy put a vibration meter on engine and he said it was twice as high as hed like to see it; but so far I have not found the root cause.

So you have a vibration just sitting still, and reving the engine, correct?
Do you get any vib while driving?
At what RPM does it start?
How bad is it? Does it come & go, or is it totally steady, all the time?

A quick check for the fan(or any other pulleys or accessories) is to loosen/remove all of the belts, and crank it up. If the vibration is still there, and unchanged, then you're looking at a harmonic balancer issue, or a clutch/flywheel issue.

If the vib goes away with the belts off, then the problem is most likely the fan you installed.