Crank problems?

The other day my bike crank started making a crack-like noise every time i pushed down on my pedal. does any body know how to get rid f this noise? Also, i've heard that automatic transmission fluid is a good synthetic lubricant for chains. Is it safe for the ball bearings or any other moving parts on my bike.

The noise might be a sign that your chain is worn out and you should get a new one, but more likely-

Your bottom bracket either needs lubricant or a new part. What kind of bike do you have? If it's BMX or an old bike you will have a different kind of bottom bracket than the newer splined kind or cup-and-cone kind. Take apart the bottom bracket, whichever sort you have (see links), and if things look dry but intact, lube them with some Park Polylube*. If not, go to your bike shop and ask for help finding a replacement part.

*For lubes: Transmission fluid is a fine oil for chains, but chains and bottom brackets, ball bearings, and threaded parts need a thicker (higher viscosity) grease. I get the kind that's specifically made for bikes because it comes in a tube that's a better size for bike applications.

The threads on the bottom bracket should be lightly lubed before screwing them into the frame. Also, if you have a square-taper type of bottom bracket, the faces should also be lightly lubed. Pull the pieces apart, re-lube, and put it back together using the proper torque. That should fix any creaking. More serious cracking sounds might be a worn chain or cassette, mis-aligned derailleur, or bad bearings somewhere.

the berrings are going bad my bike had that it gt so bad it broke the cranks get new barings

Get that checked out. I had something like that happen and then my pedal arm snapped in half while standing up to pedal.

have you made sure your crank bolts are in tight? that happened to my friend a few weeks ago..