It is an 800w corded drill and was working just fine till recently. Counter clockwise mode works full power but the clockwise mode is completely useless, drill starts at some decent speed and power(about 80-90% that of counter clockwise) but stops on the slightest contact or sometimes even before contact with anything and won't start until i switch the direction back and forth.
Add to the list of what's not broken: the clutch, because your drill doesn't have one. The gear is not likely to be broken either because transmission reversal is simply done on the commutator level on a drill like this, with a switch that swaps the brushes.
(Image from here).
The switch that does the reversal may have a damaged or loose contact for one direction but not the other. It's also possible you have a broken brush and the remaining bit is pushed away by the rotor in one direction but not the other. Less likely is a dislodged brush holder that does the same thing. If the drill is out of warranty, open it. (I don't know if the B&D warranty requires you not to open it.) If nothing looks wrong with brushes or their holders, I'd suspect the reversal switch. It may not be easiest thing to debug if it fails only under vibration; you could however temporarily bypass it with a direct connection and see if that fixes it.
Not a switch problem, as it energizes both forward and reverse.
Not a battery/power problem because you have full power in one of the directions.
I would suspect that you busted an internal gear.
Common problem, here it is in this pic, on the right side of the UL label.