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Fiesta Mk3 Brake Master Cylinder Seals???

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#1 fiestamreg



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  • Ford Model: Fiesta Mk3

Posted 02 March 2011 - 10:49 AM

Hello All

We have a Mk 3 'M reg' Fiesta 1.6 dohc.

We have been servicing the brakes on it all was going Ok until we noticed that the master cylinder was leaking fluid from the back.

We managed to get some new seals and they were changed. We then had problems getting the cylinder to pump the fluid.

I said I think that we may have put the seals in wrong(We should have noted the direction of the seals on dismantling. Ooops)

I said don't worry we will check the haynes manual.
We are now confused as the manual seems to contradict itself on the placement of the seals on the inner or secondary(As they like to call it) piston.

We originally put all the seals in the same way.

The manual can be viewed at Fiesta Mk 3 Manual Brake PDF

The picture they have is not the same as the text that is quoted below.


Note that the seals on the
secondary piston have raised lips which face
away from each other, towards the extremities
of the piston (see illustration).

So Mr Haynes which is it? Facing away from each other or the same way, as in the diagram?????

Hope you can understand our problem and that somebody knows the answer.

Many thanks


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#2 fiestamreg



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  • Ford Model: Fiesta Mk3

Posted 04 March 2011 - 09:50 AM

Think we may have solved the problem. We think the diagram is definitely wrong. The seals on the inner (secondary) piston should be opposite as the text says.

In the diagram seal 'E' needs to push fluid and it cannot push anything the way they have it. This one is the one that is the wrong way round in the diagram. The other seal on the inner piston needs to stop fluid from the first piston going past it and back up into the tank when the pedal is pressed. This one is right in the diagram.

Both seals on the primary piston need to go the same way as shown as one pushes the fluid and the second just stops fluid draining out of the tank when the first seal passes the hole from the tank to the barrel.

We found an old manual from a mini that had dual circuit brakes and this had a better diagram in it and although it didn't tell you which way the seals went around it was easier to see and work it out.

Asked at the local garage and the mechanic there agreed that we were right.

Thanks to anybody who had a look and used some grey cells on this.


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