Correct position of the brake pedal when free and when pressed all the way (working stroke of the pedal) serves as one of the criteria for checking the serviceability of the brake system. At the same time, the position of the pedal largely ensures the proper operation of the system. If the pedal is located at a distance from the floor that is greater than the standard, incomplete release of the wheels is possible when releasing the pedal (in this case, there is usually no free pedal travel). If the pedal is too low, the brake efficiency may decrease due to a decrease in the pedal travel. The pedal position cannot be adjusted; it is provided structurally if all brake drive components are in good condition. If the position deviates from the nominal value, check the condition of all drive components and assemblies, and replace any that are faulty.
1. Start the engine, let it idle and press the brake pedal vigorously several times.
2. Pull the brake pedal up with your hand until it stops.
3. Release the pedal and measure the distance from the pedal pad to the floor.
NOTE: The ruler must be installed perpendicular to the floor plane.
4. Press the brake pedal firmly until it stops.
5. Release the pedal and re-measure the distance from the pedal pad to the floor in a free state. The pedal should return to its original position at the distance from the pedal pad to the floor measured in step 3.
6. Check the free travel of the brake pedal by moving the pedal by hand until the pedal stops moving without resistance. Determine the free travel value using a ruler; it should be 1-3 mm. If the free travel does not match the specified value, it may be due to the following reasons:
- increased play in the connection between the vacuum booster pushrod and the pedal. This may be due to wear of the pushrod retainer;
- pistons seizing in the master brake cylinder;
- jammed plunger in the brake booster.
7. If the distance from the pedal pad to the floor during repeated measurement (item 5) is less than the value measured in item 2, this indicates that the pedal is stuck on the axle, that the pistons in the working and master cylinders are jammed, or that the compensation holes in the master brake cylinder are clogged.
NOTE: The expansion holes in the master cylinder may be blocked by seals that have swollen due to petroleum products entering the system, or due to the use of low-quality brake fluid.
8. If the pedal stops almost at the floor when pressed, this indicates that there is air in the brake hydraulic system or that the brake pads and discs are worn to the limit. If there is air in the system, the pedal stops further from the floor when pressed several times ("pumps up").
WARNING: If the pedal is pressed all the way down and held in this position and gradually moves towards the floor, there is a fluid leak from the hydraulic drive or the brake master cylinder is faulty. These faults are very dangerous, so immediately find the leak and fix it or replace the brake master cylinder!