74LS163 Counter Exhibits Constant Voltage on an Input Pin
Inputs of bipolar TTL (74xx, 74LSxx, and others without a "C" in the middle) parts source current, so require a fairly low resistance to ground to be recognized as a low.

You may need to draw up to 0.8 mA from the Clear input pin (and most others) to get the pin below 0.4 volts, so it will recognized as a Low.

CMOS versions (74 AC, 74HC, etc) have very high impedance inputs, and should work with your Clear circuit, if you add a 100K pull-up resistor, although I'd use a 10 K pull-up, and reduce R12 to 1K or so.