Hmm so I was investigating the lack of brakes, checked the slave cylinders and brake hoses and all looked OK. The fluid was very low in the reservoir and I topped it up but still no joy. A quick check under the dash was followed by a floorpan full of brake fluid



So, the question is:
Rebuild the existing one - I'm assuming it's the original standard 850 one
Replace with an equivalent drum one - GMC171
Upgrade to a Cooper S - GMC172 - assuming it'll work with drum brakes? I may upgrade to discs in the future.

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With new single outlet brake master cylinders there is no functional difference between drum and disc.
The GMC172 has a large metal reservoir and the GMC171 has a plastic reservoir. Internaly they are the same.

There were several different brake masters over the years and the seal kits vary depending on what one you have.
Repairing masters is not always sucessful and for the hassle of fitting them and for safety sake it's worth considering fitting new rather than repairing an old one.

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How can it be rusty when it's covered in so much oil?

I usually make the decision to re-kit or not after I have pulled down the master cylinder and checked the bore.

Just get a sponge and soak up the fluid, squeeze it back in top.
If it is the original m/c ( highly unlikely) I would just buy new one, probably cheapest way anyway. Is it original front brakes?

Thanks guys. I might extract it next and see what condition it's in. From all accounts it sounds like a really fun job..

It has been swapped to twin cylinder brakes on the front

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9 Times out of 10, they're knackered. $90 + post. Cheaper that trip in ambulance when they fail because to patched one failed. Its your life and I'm not your passenger, so its your call.

If you want to keep your master cylinder (for the sake of originality) they can be sleeved, which is highly successful. I had the original ones in my Traveller done for around the cost of replacement. They look correct and with their stainless sleeves will last at least another 60 years.

cheers
Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian

I'm not too worried with originality, as long as it works safely. I got the split pin out this morning in a couple of minutes (it looked to have been removed in the past) but the clevis pin seems to be stuck in. Going to be a pain trying to remove it..

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So true Peterb. Been there, done that, still livin after a nasty incident years ago. Yeah, sometimes you can get away with repair, sometimes you don't. And if you don't and live to tell the tale, you'll never repair again. Your life is worth more than a few bucks in savings.

Hi Tim,

I usually have my master cylinders reconditioned at Warringah Brake and Clutch. I am not sure where they get the work done but the cylinders come back with stainless sleeves and usually replated.
There are probably places in the Gong that will also do this work.

Good luck

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

After an hour or so of bashing and poking the rusted old clevis pin came out. It's unbranded so I'm assuming it's aftermarket. Not worth my while fixing then.



Seeing as the Cooper S disc one is the same price as the drum one I may as well order the larger capacity one.. Edit: decided to go with the standard drum one and a BHA4661 extension sleeve to keep an eye on the fluid level.

Thanks everyone for the help!

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Judging by the condition of the plating on the cylinder, that one was not that old. It probably would have honed OK.

Tim

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1951 Morris Commercial J Type Van
1955 BSA C11G
1961 Morris Mini Traveller
1969 Triumph TR6R
1977 Leyland Moke Californian

Disc and drum ones are usually different. One has a line pressure valve.

Isn't that the brake and clutch difference?

Be careful of them there extension sleeves; a bad o-ring and you'll have more brake fluid outside the brake cylinder. I don't use mine any more.