When it comes to ensuring the safety of your vehicle, it's important to know how to test a brake booster and master cylinder. This guide will walk you through the steps of testing these components, so you can be sure that your brakes are in good working order. First, turn off the engine and press the brake pedal several times. You should notice that the pedal is very “low” on the first pump, indicating that there is not much resistance to pressure.
As you continue to pump the pedal, the pressure should become firmer. This indicates that the brake booster is not leaking. If there are no other leaks and the hose has good suction, restrain it to reduce vacuum loss and reinsert the one-way valve into the vacuum amplifier. Next, turn off the engine and immediately remove the one-way valve from the servo motor.
If the amplifier maintains the vacuum, you will hear a loud whistle. If there is no noise or very little can be heard, check that the one-way valve is working properly. Attach the valve to the mouth and place the suction on one side and then on the other. If air can be drawn through the valve in one direction and not the other, then it is functioning correctly.
However, if air can be sucked in on both sides, it needs to be replaced. If the valve is in good condition, then it's likely that the amplifier is in poor condition and needs to be replaced. To determine if this is due to a faulty amplifier or a leaking master cylinder, observe the mounting surfaces on which the master cylinder is mounted on the amplifier. If there is brake fluid in the amplifier, then it's likely that there is a leak in the master cylinder causing deterioration of the diaphragm.
In this case, both components need to be replaced. If no problem is found right away, then you can move on to testing for hardening of the brake pedal due to front disc brakes. To do this, remove the clamp and clean off any corrosion from the slides before applying some grease to them. This type of test is usually carried out on new or rebuilt master cylinders or after removing an old master cylinder from a car.
Tighten up the master cylinder on a bench screw and use an impact screwdriver or giant screwdriver to apply pressure to its plunger. If it's too strong or cannot move at all, then it's likely that it's still working properly. However, if it continues to enter then there could be an internal leak or a faulty master cylinder. In this case, you should separate the brake lines from the master cylinder and replace it with one of equal size (IOS).
If there are no obvious problems with your brakes, start up your engine and use pliers to tighten up a hose halfway between your motor and servo motor before carefully removing its one-way valve from its amplifier. In some cases, you may need to test your brake master cylinder if you notice a brake warning light, engine control light or warning message when applying braking pressure from a stop. This could cause your engine to suffocate or cause ignition failures or stops when braking. It goes without saying that a modern brake system won't work if either its brake booster or master cylinder fails. The master cylinder controls important brake functions from hydraulics to all other brake components.
If you notice a drop in your engine at idle when applying braking pressure from a stop then it's likely that your brake booster needs replacing. Additionally, using poor quality brake fluids in your brake fluid reservoir will definitely affect your master cylinder. This implies that air has been pushed from your master cylinder back into your reserve tank which will come out of there when you start pumping your pedal with your engine turned off in order to remove any residual vacuum from your brake booster. If you notice that your fluid level in your brake master cylinder starts dropping after stopping for the first time when pressing down on your pedal then it's likely that your master cylinder needs replacing or servicing. The pressure will push hydraulic fluid or brake fluid towards your brake calipers in order for them to apply braking pressure. If you have any questions or concerns about testing your brake master cylinder then feel free to let us know in the comment box below.
