Brake master cylinder leaking

steve sturgin · 10-29-2008

Hi folks,

As the title suggests; I am having trouble stopping fluid leaking from my master cylinder. The fluid seems to seep out between the gasket / diaphragm. I have tried cleaning both surfaces a number of times now and all seems to be well until I take the car out for a spin.

The master cylinder is new as is the diaphragm so I am scratching my head.

Has anyone come across this in the past and did you figure out a way to fix it.

Thanks in advance for any help you are able to give.

Steve

bossman69 · 10-29-2008

Just a suggetion but I would take a small rubber mallot and tap all the way around the lid to give it a little bit better seal.Dont beat it hard as to distort it but lightly tap it. If that doesnt work I would remove it and take it back as defective.Hence! the tapping the lid lightly so if it doesnt work you can still get you a replacement.

steve sturgin · 10-29-2008

Hi bossman69,

I was thinking perhaps the lid also, it seems like the area that is supposed to help make the seal is a more narrow than the surface of the master. I can't get hold of my parts supplier as they are up at your end of the globe so i might have a go with the rubber mallot.

Thanks Steve

rocky289 · 10-30-2008

Steve there was a similar thread here a couple of weeks back.
Is it leaking because it's overflowing?
Is there too much fluid being displaced by the braking action & forcing it out?

steve sturgin · 10-30-2008

Hey Rocky,

The fluid is about half full so i think it's ok.

I have been taking a look at the lid and found that there was a bit of a warp in it so i have modified it a little, cleaned the master up again and am going for a whirl while there is still a bit of daylight for a test.

Steve

steve sturgin · 10-30-2008

Hey folks,

Still leaking, have to go back to the supplier i guess.

Steve

rocky289 · 10-30-2008

Is it the same as the previous one?
Is the reservour for the disc brakes the same size as the other one?

The Greek · 10-30-2008

The drum brake M/C has equal size reserviors and the disc brake M/C has large and small ones.

I have found that many times it isn't the cap that is warped, it's the clamp is placing uneven pressure on the cap. One side will be held down with more force than the other. All that you need to do is to bend the clamp so that the cap has equal and sufficient clamping force placed on it.

steve sturgin · 11-01-2008

Thanks folks for the feedback,

Rocky: it is the disk type with one smaller and one larger.

Greek: i am reluctant to bend the clamp as it seems to be exerting a lot of presure at both points where it makes contact.

I thought i might leave it until the parts supplier(Southern Mustang) gets back from the US so i can quizz them. But one more stupid question: Which way does the gasket / diaphragm go in, with the sticking out bits upwards or down into the fluid ??? At present it is up.

Steve

rocky289 · 11-01-2008

Steve
Been a while since I've seen one of these so can't advise you about the diaphragm without seeing it.
It has to be arranged so it can move up & down to follow the fluid displacement. The cap is vented but the cylinder is not.
From memory some of them used to have "fluid side" written on them.
A few questions.
Why did you replace the M/Cyl?
Is it the same as the previous one?
Is the larger chamber conected to the disc/front line?

steve sturgin · 11-01-2008

Hi Rocky,

I had a go at what The Greek said and bent the clamp / bracket a little, my leak seems to have got better so i am going to bend a little more.

Steve

steve sturgin · 11-02-2008

Hi Rocky,

A couple more answers for you:

The car came with a falcon M/C that didn't work also front spindles rotors and brakes from a falcon that didn't fit. I have kept the rear drum setup but have changed the rest over to powered 4 pots on the front, the M/C is matched to the setup i have (i am told). The fronts are plumbed to th larger chamber all via a matched prop' valve.

There is no fluid side written anywhere on the rubber but for the moment i am leaving it pointing downward, it seems correct this way but i am still not sure.

I had another go at bending the clamp yesterday and took it for a longer drive, the leak has almost gone now so i guess we are on the right track, I will bend a little more, clean it all up again and report back in a couple of days.

Thanks for all the help guys.

Steve

rocky289 · 11-03-2008

Steve

Not really sure what your questions are there.
Sounds like you might be getting close to sorting it anyway.
Was it just the fronts that were leaking.
When I read through your profile I saw you had the 4 potters on there & realised you would be displacing a bit more fluid than with std. May have to keep the level down a bit in that chamber.
Check it out with Wayne when he gets back from the US, he'll sort it for you.

The Greek · 11-03-2008

Steve, the gasket is supposed to be with the "sticking out bits" facing upward into the cap. The Ford assembly manual states that the proper brake fluid level should be 1/4" to 1/2" from the top and the larger rear reservoir is plumbed to the front discs.

Keep tweaking the hold down clamp, you're almost there. Make sure that the top sealing edges on the M/C are clean and smooth.

The gasket will sometimes get particles of rust embedded into the rubber where it makes contact with the M/C. Scrape it off if there is any present.

steve sturgin · 11-19-2008

Hi again,

The leak persists. The gasket is now on the right way round, all surfaces are clean, the clasp is bent as much as it can be.

Perhaps i am missing something here, i did not bench bleed the master cylinder before installation because i have no idea how to do this, any advice.

I was also told that perhaps there is a problem with the booster (new also) forcing air into the brake system.

Any assistance welcome.

Steve