Odd shaking/rumbling...

[GBSilviaS15]

I have a 95 240sx.

I get crazy shaking at low rpms (1000-2000 range) when I'm slowly letting off of my clutch and adding gas to accelerate. It also shakes a little bit when shifting into second because I have to ride the clutch a little to make a smooth shift. Pretty much when I just ride the clutch the let the car start rolling, it shakes like crazy!

This started happening after I replaced my front oil seal, in which I found a little crack down the inside of my crank. Could it be possible that the crank is just slipping or misaligned or something? Is the crank pulley supposed to have some kind of notch or something it in to fit the shaft? Is the shaft supposed to have some kind of notch or something to hold the pulley? Could I be running low on transmission fluid?

Any help is appreciated.

[InsanityInc]

Yeah, the crank has a key and the pulley has a notch. If you didn't put it back on right that could definitely be your problem. Otherwise it sounds kind of like a warped flywheel.

[GBSilviaS15]

If it's not the crank pulley, it'd probably be one of the clutch components coming loose...