1992 SC400, went to stop and the brake pedal has become very hard like no power assist brakes.
It will barely hold the car stopped if in drive at a stop light.
Has anyone experienced this before and what could it be?
Tia,
Nicholas

 

Hard brake pedal is usually brake booster related. Check the vacuum lines connected to your brake booster for any cracks or leaks. If there aren't any, then look into replacing your brake booster.

 

Have you had any brake work performed lately?

Double check the vacuum lines to the brake booster and there may be a check valve, too. Make sure the valve allows air flow one direction only and is installed properly.

Quick and easy brake booster tests
Car turned off
Pump the brake pedal, each time the pedal height should get higher until it's stuck at the top. You're slowly taking out all the vacuum in the system.

Next keep your foot on the pedal with pressure and start the car. Brake pedal should drop down as you've now introduced vacuum back to the system.

If it fails to perform either of these it normally means a bad booster. But double check the easy stuff because boosters aren't fun to replace. Nothing under the dash is fun!