Master cylinder changed and still the brakes are w**k!!!

I changed the master cylinder a few weeks ago and put new fluid in and bled the brakes. All was great for about 3 days then the pedal started hitting the floor again with no resistance.

I used my pressure bleeding kit again and checked there was no air but i realised that the 2 brakes which are fed from the front end of the master cylinder, i think its the secondary chamber, were literally dripping fluid out slow as hell when there should be a good solid stream (pressure kit was set to 12-15psi). The other 2 brakes bled great.


Is the new master cylinder nakered?? seals leaking?? or return spring stuck??

If i pump the brakes, sometimes it might have some resistance but then it will go again

Try bleeding the brakes at the master cylinder, you will need 2 people and get some one on the brake pedal, losen the joint between the master cylinder and brake line and get the brake pedal pressed to the floor slowly, brake fluid should spray out so get a cloth to catch it, when the pedal is still on the floor do up the connection then repeat a couple of times then move onto the other brake line.

If you are still getting problems is the any restrictors on the brake line?  

Gti?

Have adjusted the brake compensator?

Ive just taken the master cylinder off and as i depressed it, the main piston wasnt springing back straight away, it was taking ages so i took it apart and one of the seals was in bits this was a new part so ive just ordered a new on off euro car parts

How do i adjust the brake compensator?? I think ive heard of it before but i dont know if or where i have one

If you have one its connected to the rear beam by the side of the petrol tank, (near side) you can see as the rear of the car goes down (heavy load) the compensator opens and allows more fluid to the rear brakes. If you have a cab don't think you have one.

Later cabriolets have 2 large cylinders fitted just underneath the master cylinder on the rear brake lines which restrict the flow of brake fluid, I don't think you can do anything with them.

Ive had a look and the only thing i have in the lines for the rear wheels is the proportioning valves. Ive had these apart a while ago and the seals were fine.
Well at least i know then that ive not wasted my money on 2 new cylinders because it cant the the compensator as i dont have one. Its a start i guess.
Can anyone confirm though that when you fit a new cylinder, along with bleeding the system, there isnt anything else i need to set up. its a simple bolt on the the vacuum with the o-ring and then away you go etc.

It should be as you stated bolt on bleed up and away you go. Good luck.
Martin.

Thanks Martin. i pick up the new cylinder tomorrow so should only take an hour or so to fit and bleed through. best bloody work this time haha.

Might sound daft but you dont need to prime the cylinder first do you with the new fluid before you fit the fluid resiviour etc?

When doing mine I bleed the master cylinder to make sure no air is trapped