Ford Repair Questions? Ask a Mechanic for Answers ASAP
Hello. My name is Mark and I will be assisting you today.
This sounds like you have a faulty master cylinder.
Air is probably entering it at the rear seal where the push rod enters it.
Thank you for your reply.
Thank you for your rel
Thank you for your reply and appreciate the concept. But can you enlighten me more on how the air is entering pass the seal besides, it being worn? Where in the piston stroke does the air actually enter the system - what is the process that allows the air to enter? Is it purely the piston going backwards and forwards? If so at what point is the air being taken into the system?
What is the process allowing the air to enter? Is it happening at atmostphere pressure or is it being pressurised some how?
The rear seal will most likely be worn at the point where the push rod enters.
The thing to imagine here is how a servo works. On one side of the membrane is atmospheric pressure and the other side is lower than atmospheric pressure. (Under vacuum). However vacuum doe not mean there is no air inside it. It is only a pressure differential. When you press the brake, it is this pressure differential that gives you the brake assist. ie. it is only atmospheric pressure acting against the lower pressure. Any air in the lower side is normally pushing against the rear seal but doesn't get past it. If the seal is worn then this air can enter the master cylinder.
If you look at the diagram you can see the chamber where the push rod enters the master cylinder.
Having bled the system and pushed all air bubbles out, and accepting there is no air in the system and do not use the pedal to test pressure, will air enter or will air only enter after having tested at the pedal? Even so, which ever is done no pedal or pedal and no fluid escapes from rear seal, when is the air entering? Is the air entering on the forward stroke or on the rerurn stroke
Having bled the system and pushed all air bubbles out and accept there is no air in the system, and do not use the pedal to test pressure, will air enter, or will air only enter after having tested at the pedal, even so which ever is done no pedal or pedal and no fluid escapes from rear seal, when is the air entering? Is the air entering on the forward stroke or on the return stroke as in brake on or brake off? Is this when air would enter even though there is no fluid escaping from the rear seal? Thank you.
Remembering there is equal volumne of air out of all four corners.
Air probably only enters on the forward stroke. Have you tried clamping all four brake flexi hoses to see if the pedal goes hard. If it does then fault is after the clamps. If not then fault is before the clamps.