Trouble bleeding brakes

[phoenix]

Hi I am trying to bleed the brakes on an S1 4.2 . It is a completely new system and I bled the rear first and got a firm pedal. But when I try to bleed the front a little fluid comes out of the servo outlet to the front brakes. (with hydraulic line off) I have tried a different servo which has been refurbished and its still the same . All new lines and cylinders . Any thoughts ?

[mgcjag]

Check the holes are drilled right through into the cylinder on the connections.....it has been known before that they havent been drilled deep enough.....or a blockage from reservoir to servo.... Steve

[phoenix]

I have tried two different servos and cylinders with no joy . It seems a little strange that we got a good pedal after bleeding the rear although after being left a short time the pedal goes to the floor .

[Joes66]

What does "little fluid comes out of the servo " mean?
No fluid whatsoever should leak out of anywhere on the system
Sounds like whoever re built and or replaced the braking system on your car has got something wrong
Could be pipes in the wrong holes or worse
Take it to a professional and have it checked over
Joe

[phoenix]

There are no leaks on the system (two of us have checked it against diagram for routing) This is a brand new system all calipers all lines servo and master cylinder . When we first bled the system we stated with the rears and strangely got a firm pedal. When we tried to bleed the front we got no fluid out of the servo cylinder. We took the union off the brake line at the cylinder pressed the pedal and only a little fluid came out. I have read on the forum it is most likely the second piston in the servo cylinder that has travelled to far .I have now emptied the servo cylinder and I was thinking of using one of the bleed nipples on a front brake to feed fluid back to the servo cylinder .Any thoughts its very frustrating .

[abowie]

I was thinking of using one of the bleed nipples on a front brake to feed fluid back to the servo cylinder .Any thoughts its very frustrating .

That is what I would try next.

[MarekH]

As it is the first time, I would also dissolve or pack as much red grease into the brake fluid as possible. The reasons are twofold:- firstly, you need to lubricate the seals and make sure they can move freely (and your servo is already assembled...); secondly, you get a visual indication of where the fluid is going and whether it has got through or not.

This is also one way of verifying that the seal in the servo is holding up properly:- if you have red brake fluid in the front circuit but find the rear circuit has a tinge of red, then it is confirmation of a leak at the seal in the servo.

Bleeding a completely brand new circuit with meths first time around before you have started is also sensible. It is thinner, flows more easily and flushes out any debris easily. Once "fully submerged", the brake fluid will go through more easily.

kind regards
Marek

[phoenix]

Thanks to you all I will try again Monday .

[phoenix]

At last got working brakes . I took off the front brake delivery union off the servo cylinder and filled with fluid from a dropper till it flowed out off the feed from the reservoir . ( I had taken the feed off). Then I used a low pressure bleeding kit that uses a spare tyre at about 15 psi and connected to the brake line to the front brakes and bled them as normal the connected it back to the servo cylinder and hey presto brakes. I think it is just the internal valve in the cylinder that was causing it .
Just put the last awkward nut on the fuel pump mounting . Most of the work was done by the mechanic working with me but this last on was a B??????d. We gave up at the time fed up and came back to it .
Next I think will be setting up the rear suspension .