Кажется, как если бы главный тормозной цилиндр имеет ошибку. Регистрируйте транспортное средство с дилером и сделайте так, чтобы они установили это.

i don't understand your language but i Guess you mean

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am i Right

Well you're almost right, what he was actually saying was;

你的头很不好！我无法想像你为什么这样做！

If your pedal is fading after you purge air from the system there is a good chance that the master cylinder is bad. It can also mean that you have an improperly installed brake pad, leak, or binding in the system.

The bubbling of brake fluid in the reservoir when depressing the brake pedal is a condition I have always called bypass. And this condition is a common sign of master cylinder failure in GM trucks of that era.

One final test to conclude that the master cylinder is bad is the line-lock test. The test involves lightly restricting your three rubber brake hoses (front left, front right, and rear center axle) with a line lock tool. Be careful not to crush the brake hoses as they can be permanently damaged. A slight compression of the line will restrict fluid enough to stop flow to the wheels. After line-locking the brake hoses, depress the brake pedal. If the pedal still fades then you need a new master cylinder. If the pedal grows stiff, then remove one line-lock at a time until the pedal drops. The dropping wheel houses your problem.

Do a google search for brake line locks to get an idea of what you would need as some auto parts stores carry them. Personally I use vice grips, but I know from experience how little pressure to apply to the hoses to keep from damaging them. If you do use this alternative, be very gentle.

master cylinder seemed to have been the problem,thanks for the help

"That's what message #1 said.

Кажется, как если бы главный тормозной цилиндр имеет ошибку."

It seems, as though the main brake cylinder has a fault.

"Регистрируйте транспортное средство с дилером и сделайте так, чтобы они установили это."

Check with the dealer to make sure.

Jon

Is the line lock an actual recommended process? I have never heard of compressing the rubber brake hoses. Is this the cause of the odd internal brake hose issues I see on occasion?

Replace the master cylinder as long as:

1) You have not let the resevoir get extremely low and got air in the system.

2) You did not just recently replace it and never bench bled it.

Cannot say that I have ever read a manufacturer's braking system diagnostic tree. But I have seen many unnecessary master cylinder replacements due to various issues at the wheel. After all, they do make line lock tools commercially available.

I would like to think most restricted brake hoses are caused from years of flexing, stretching, and bending. But you are correct that improper techniques can damage the hose.

I notice no mention of a shop manual or such in the discussion. With modern brakes, they must be bled in a specific sequence (found in the manual) to be sure you have all the air out. So much better to do it right the first time rather than to have to do it again.

Bill