Two pump brake pedal

[basilruler1234]

Hello, I am hoping for a little advice

I have a two pump brake pedal, first pump goes low and then on the second pump the pedal is at the correct height and hard, and whilst held there it doesn't sag.

I have bled the system extensively, no air.

Brake cylinders are good.

No loss of fluid from the reservoirs.

I have performed the test to exhaust the vacuum tank by repeatedly pressing the pedal, it becomes hard and high, foot on the pedal, start the engine, pedal then drops slightly as expected as the servo assists.

I have ordered a seal repair kit for both the master cylinder and servo, with the above information, which do you think is the likely culprit.

thankyou James.
Series 1 4.2

[mgcjag]

Air in the system......old school way to bleed is the way to go.....open nipple...press pedal down and hold it down and close nipple....either use a helper of a length of wood to hold pedal down....release pedal......repeat....do not let the pedal up if a nipple is open...so no pumping....Steve

[basilruler1234]

Yes, this is how I've done it, I've bled the system this way several times, I don't believe there is any air in the system.

[Tommd]

Air in the system is the first concern.
More details. Does it do it even sitting still without the car moving? How long must one wait from the two pumps that bring the pedal up until the pedal now drops low?
If not air I would suspect a caliper piston is retracting too much. If the problem only occurs while the car is in motion, I would check for a warped rotor that is pushing the pad piston back too far. If it happens without the car in motion, I would check for a caliper piston that is retracting too far due to seals or a messed up retract pin system in the caliper.
Remote possibility a weak rubber hose that expands partially on pressure.
Tom