g'day all i have a problem with my brakes at first i thought it was just air but i think that maybe it isnt. i have bled and bled my brakes but still doesnt fix my problem, the problem is as follows i get pedal for my brakes, keep pressure on the pedal and it slowly releases pressure until the pedal is to the floor i then release and it does the same thing.......i think that maybe im in for a new master cylinder but i dont know what do you guys think?

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1964 smooth roof panel van
1967 Mk 1 X-Police cooper s
1970 mini k
1975 leyland

yeah, sounds like fluid leaking past the seals... if it's the car in your avatar & signature, then you can safely say the MC needs reconditioning or replacing. You can get the old one reseleeved and new seals put in - personally I've never resleeved them, I've put seals in a few and never had them fail, but I check the bores for pitting.

You won't be able to buy a new master cylinder the same as the original for your car, and the it is different to a standard mini as it has a taller tank. Morris 1100's had the same one - not sure about the bore, but I'd guess it's the same

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did I tell you that I won a trophy?

yea no it isnt the car in my avatar that is my cooper s resto. its a 1970 mini k . i have another mc should i replace them and see how i go?

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1964 smooth roof panel van
1967 Mk 1 X-Police cooper s
1970 mini k
1975 leyland

you could, but you might just be replacing a stuffed one with another stuffed one.

You can test the spare one a bit though - if you have a bleed nipple (hint - the calipers on the front of your S will have them), wash out the MC with metho, then fill it with fluid, and put the bleeder in the outlet. Then push down on the top of the MC with the plunger on the bench - effectively pushing your foot on the brakes - it should be rock hard. If it's hard, then it ought to work in the car, but no telling how long it'll last with your right foot bashing against it with a whole lot more leverage than your hands on the bench

Good idea to use the bleeder to isolate the problem on your car as well - put the bleeder in the outlet on the MC and push your foot on the brake - if the pedal still sinks, then the problem is the MC, if it's hard, then one of the wheel cylinders might be leaking, or a hose about to burst, or something. But with your symptoms you'd probably know if a wheel cylinder was leaking because you'd be losing fluid

DISCLAIMER!! make sure the bleeder is tight, shield your eyes etc. etc. and if you get covered in brake fluid, don't hunt me down

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did I tell you that I won a trophy?

what condition are your (rubber) hoses in? if they are old the fluid could be causing the hoses to swelling up under pressure instead of forcing the shoes into the drum...

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78 Leyland Mini - Prince

this really is a can of worms, I would first screw a bolt into the MC. Get in car and press the pedal. It should be rock hard. Then just work your way forward. If your rubber hoses are in good nic, you could clamp em 1 at a time and see if you can isolate the problem.


test MC first.

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yeah that the best solution. start at the top, and work your way down.

sidenote: did you bleed in the correct order? i think it's furthest from the MC ---> closest

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78 Leyland Mini - Prince

From a BMC workshop manual....


If you don't know how old the brake parts are change them. There is a fair chance that you are playing around with 40 year old brake seals and hoses. It does not take a lot of effort to change them. It could work out a lot cheaper than not changing them.

My guess is that a master cylinder seal is leaking.

replaced the MC and fixed the problem thanks for all ya help again fellas.

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1964 smooth roof panel van
1967 Mk 1 X-Police cooper s
1970 mini k
1975 leyland