springs master cylinder

[sylvain]

Hello, I revised the master cylinder of my fulvia, I have a doubt on the position of springs, the longest is between both pistons or opposite, master cylinder of 18 mm, thank you

[Huib]

The longest one is between the pistons.
The one with the thickest steel wire is at the end.

The way I remember this is as follows.
The spring at the end has to push back two pistons and is thus the strongest.
If the piston at the end is stuck for some reason, the spring in the center has to push back the first piston over a longer distance and is thus the longest.

[sylvain]

thank you

[Bryan]

I have recently had the brakes overhauled on my S1 Zagato with 4 new brake cylinders on the front and a revision kit for the master cylinder. In the beginning I found the pedal travel to be a bit longer than expected but the brakes worked fine and the car pulled up in a straight line. After a short run today the pedal became very hard and it was clear that the pressure was not releasing as it became impossible to drive due to the brakes being locked on. I opened a bleeder on one front caliper to release the presure and all returned to normal. My idea is that the master cylinder is at fault and on reading this thread I wonder if the springs being in the wrong place could explain my problem..
regards
Bryan

[Huib]

I think you are right in diagnosing that the cause is in or near the master cilinder as both front brakes lock.

I am not sure if a spring swap is the only factor. My feeling is that if the springs are in the wrong place, they may contribute.

There should be some free play between the pin on the pedal and the plunger of the master cilinder. The amount of play is not important, 1 mm is enough. There is an adjust bolt above the pedal.

Is the spring on the pedal still there?

How are the plastic bushes on the pedal spindle. Plastic of the 60's is rather unstable. They absorp moisture and expand. Also the coefficient of thermal expansion is higher than for most modern types of plastic.

I don't think the level of the fluid matters.

[racing]

Did you check the brake hose.If they are to old the innerdiameter allowed to brake depent on the high presure
but the brakefluid can not flow back. The hose inner diameter is reduced/ closed by soaking ( hope that is the right word)

regards Andreas

[Huib]

What Andreas means is that old hoses may be clogged inside. The high pressure from the mastercilinder pushes the hose open and applies pressure to the piston in the wheel brake cilinder. The tiny retraction force from the sping inside the piston in the wheel brake cilinder will not be able to push the fluid back into the master cilinder.

It is worth checking. I moved it down the list of possibilities as I understood from your posting that both front brakes lock solid preventing the car from moving at all. I doubt if a clogged hose will result in such a solid lock. It is also unlikely that both (left + right) hoses go bad at exactly the same moment after work on the master cilinder.

[Charles]

I've experienced this on my '69 FIAT 124 spider. It was caused by a mechanical problem with the pedal itself so it might be worth to check that area too.

[georges2]

I am always surprised, (and quite afraid) in seeing how many differences there are between different model cars...
I own (only one) 1300 S1 Rallye, fitted with a master cylinder on which a little metal label says "19mm"
there is also a servo working on front wheels.
I took a picture some years ago when I dismantled it
The 2 springs have same lenght, but not the pistons...
It works well since
Best regards

[Bryan]

Thanks to all for the good advice which I couldn't respond to for technical reasons (long story now solved !) but greatly appreciated. The latest on my brakes is that the master cylinder springs were in the right place, there was some freedom on the push pin of the pedal, the pedal rotates freely on the spindle and the spring works. My first action was to check the hoses and although they looked perfectly OK I found 02/84 stamped on them which I took to be the date of manufacture. As this seemed very old I replaced both front and rear hoses and flushed the system (fluid was not clean). I also decided to bite the bullet and changed the master cylinder (from Martin Willems). It has a cast iron body but was only available in 19mm (so goodbye originality). After bleeding yet again I have brakes that work, however I am still not 100% convinced that the brakes are as good as they should be. Although driveable now, I would still like a harder pedal with a bit less travel but have no other Fulvia to compare it with. As pumping the peddle has no effect I assume that trapped air is not an issue.
A reliable friend has suggested the pads may be at fault but I cannot see how they could affect the hydraulics. Apart from the discs and pads I have changed everything else !!!