Help! My brakes are pumping down!

[Freddie W]

I have just replaced my brake master cylinder as my brakes were not holding pressure and the pedal starts to sink when you hold your foot on the brake. I was told it was the seals in the master cylinder and so replaced it.

Now when I try the brakes they are initially good and firm but if you pump them they get worse till they go straight to the floor... They are pumping down...

Can anybody help as I have no idea why this is happening. I've spent the whole afternoon bleading the brakes which did nothing and normally if there is air in the system they pump up.

Any suggestions would be great.

Cheers.

[Retroanaconda]

I'm no expert on braking systems, but I would be inclined to check the flexi pipes for any bulging under pressure, and then the pistol seals in the calipers themselves.

[Freddie W]

Quick Update.

I have bled the whole system again and now the breaks are really good unless you pump them really quickly, almost like hammering on the pedal, if I do this then they go soft again.

Could it be because hammering on the pedal is dislodging air in the system?

[dantd5]

Quick Update.

I have bled the whole system again and now the breaks are really good unless you pump them really quickly, almost like hammering on the pedal, if I do this then they go soft again.

Could it be because hammering on the pedal is dislodging air in the system?

Freddy this is a very serious issue actually. I just changed my caliper and brake disks. Mine just wouldn't catch. Bleed from Left back to right back and then rihgt front and left front. Let them bleed thoroughly and it would need no hammering. If it is the 2-man method , make sure the brakes are totally hammered to the base and then loosen the screw on the caliper... good luck..