[Mike_The_Grad]

Originally Posted by RichardJ

>>each piston displaces brake fluid proportionately to their input,(some biasing takes place to prevent premature application of the front brakes and over application of the rear brakes.)<<

Neither is true.

>>You must keep the pin depressed while bleeding the brake system or your brake system warning light will turn on inside the dash cluster<<

Also not true. The pin is the end of the Metering Valve that is housed inside The Combination Valve. The Warning Switch operates independently from the Metering valve.
The Metering Valve HOLDS OFF fluid from the front brakes until line pressure reach's 40-60 lbs, depending on application. This holds off application of the front brakes until the rear brakes can begin to work and prevents nose-diving of the front end.
The Warning Switch Piston does not move if the pressure on both inlet ports is the same. 100lb on the front and 100lb on the rear port, the piston does not move. 600lb on the front port and 600lb on the rear port and the piston does not move. Sometimes there are springs on the front and rear of the switch piston so there can be some variation from equal pressure before switch contact is made and the light comes on.

"Brake pressure from the front and rear port are the same as long as there is no failure in the MC or any other part of the brake system."
True statement.

each piston displaces brake fluid proportionately to their input.
Also a true statement.(layman's terms)


The Metering Valve HOLDS OFF fluid from the front brakes until line pressure reach's 40-60 lbs, depending on application. This holds off application of the front brakes until the rear brakes can begin to work and prevents nose-diving of the front end.
True statement.

some biasing takes place to prevent premature application of the front brakes and over application of the rear brakes.
Also a true statement.(layman's terms)

The warning Switch Piston does not move if the pressure on both inlet ports is the same.
True statement.


>>You must keep the pin depressed while bleeding the brake system or your brake system warning light will turn on inside the dash cluster<<

I apologize for this statement, as it needs some clarification.

"The pin" that is "depressed" in actuality is a preventative precaution. And is not so much "depressing" it, but rather preventing the "warning piston" from becoming un-centered during the brake system bleeding process.
If air is present between the outlets of the MC and the inlet ports of the "combination valve" this can result in an un-equal pressure variance between the front and rear brake systems.
It is possible that no air exists in this section,which would allow you to successfully bleed the brake system without an un-equal pressure variance between the front and rear brake systems.

But, how likely is that?

The factory service manual instructs the technician to take this precaution while bleeding the brake system, so as to avoid the added time of re-centering the warning piston when it could have been prevented in the first place.