Brake problem - pedal going to the floor! - fixed

[DaBigGinger]

I've recently had one of my brake calipers off to remove the suspension strut. Since having it re-fitted, and new brake fluid filled up and bled etc. (no other work was done on the brakes), if I press the brake pedal lightly, over the course of 10-15 seconds, the pedal will go to the floor and will not do anything unless I release and re-apply the brakes.

However, if I press the pedal really hard and hold it, it doesn't go to the floor. The pedal travel stops roughly where I would expect it to. It stops quite capably if I press the brake pedal hard still!

Am I correct in thinking that there is probably some air in the system, or could the problem lie elsewhere? I'm just a bit puzzled as to why the pedal will not sink to the floor when I press it hard.

[PeteG40]

i'd rebleed - preferably with a pressure bleeder and try again,.

[grayg40]

sounds like air, the way i do my brakes and havnt had a problem is
You need two people and a good bit of fluid. one to pump the pedel and watch the fluid level and the other to slacken/tighten the bleed nips. starting from O/S/R, N/S/R, N/S/F then O/S/F.
Slacken first nip(O/S/R) a little till you see the fluid running out and get the other person to depress the pedal slowly all the way to the floor, holding pedal on the floor nip up the nipple and take foot off pedal, re check fluid level.  do this about four times to each corner and see if that makes a differance.
 

[DaBigGinger]

Bled the brakes, a little bit of air came out, the pedal was just the same. Gave up, took the car down to the garage and they put the power bleeder on it and I swear it's worse now! They're suggesting either my master cylinder is knackered or the master cylinder which is part of my remote servo could be. I've got a spare master cylinder, so hopefully it's that.

What's I think is weird is how the pedal just goes to the floor if I apply a small amount of pressure, but not if I push it hard. I can push it really hard and as I slowly reduce the pressure, then the pedal goes down. Similarly, if I press it softly and it starts going to the floor, then push hard, it stops going to the floor and toughens up!

[scotsjohn]

That could possibly be due to your pressure regulator action. Gentle pressure over all the system, but bang on the pedal and the rear brakes are seeing less action. If that's the case I'd concentrate on the rear brake bleeding and shoe clearances.

[Nick_S]

He may not have the rear bias valve fitted on his car, its a mk2 conversion.

[DaBigGinger]

Nope, I don't have a bias valve on mine. I do have a remote servo, but that's only 5 years old. I'm going to hand it over to the garage in a few days and they're going to take a look. I don't know a massive amount about brakes and I'd rather not make a mistake with those.

[DaBigGinger]

New master cylinder fixed it. Thanks for your help and suggestions.