ASE A5 Hydraulic Testing, Bleeding and Fluid

Question 1

A vehicle with a conventional dual-diagonal split hydraulic system is being bled, and the manufacturer gives no special sequence. Which wheel should be bled first?

Accepted Answer

The wheel farthest from the master cylinder

Answer

Bleeding normally starts at the wheel with the longest line run from the master cylinder, which is usually the right rear. Air is then pushed out of the longest circuits first.

Question 2

Why must a brake fluid container be kept tightly capped when it is not in use?

Accepted Answer

Glycol-based brake fluid absorbs moisture from the air, which lowers its boiling point

Answer

DOT 3, 4 and 5.1 glycol-ether fluids are hygroscopic and absorb water. Absorbed water lowers the fluid's boiling point and promotes corrosion.

Question 3

A technician is told that a customer previously topped off the reservoir of a vehicle with DOT 5 silicone fluid. The system is now to be serviced with DOT 3. What is the proper procedure?

Accepted Answer

Fully flush the system with the specified fluid and replace any contaminated seals and hoses as needed

Answer

Silicone DOT 5 does not mix with glycol-based DOT 3, so the system must be completely flushed. Seals that were exposed to the incompatible fluid may need replacement.

Question 4

A technician is pressure bleeding a brake system. Which of the following is the correct practice?

Accepted Answer

Pressurize the system to about 15 psi using an adapter that fits the master cylinder reservoir

Answer

Pressure bleeders typically run at roughly 10–25 psi through a proper reservoir adapter. Higher pressure risks damaging seals and the reservoir.

Question 5

A technician has just installed a new master cylinder. What should be done before it is connected to the brake lines?

Accepted Answer

Bench bleed the master cylinder to remove air from its bores and outlet ports

Answer

Bench bleeding removes air trapped in the master cylinder bores before installation, making the later system bleed much easier.

ASE A5 Practice Test

ASE A5 Practice Test

ASE A5 Hydraulic Testing, Bleeding and Fluid