Not really true.. You don't *need* a larger master cylinder can ..unless your name is Aaltonen or Makinen.

With the Finns indulging in their technique of left foot braking, the engineers found they could use up a set of pads in one stage..  And, as the fluid level drops as the pad material disappears, it was possible to use all the fluid in a standard cylinder before there was any chance to top it up.. Solution?? more fluid = bigger master cylinder can.... which became standard on all Ss.

So if you do have S discs and a small can cylinder it might be worth checking the fluid level every now and then.  I find once a year adequate because I know my pads will last longer then that.

Cheers, Ian

No need to talk about force on pads or rate of pad wear, it is simple. The S calipers require a greater volume for their full travel, hence the larger reservoir. Spin it however you like, the BMC Engineers, as this was quite a while before the BL merger, were simply doing their job. Note that the larger reservoir MC was also used on the ADO16.

Also, more relevant to this thread, I think my second parts order from Mini City in Fairport NY in the spring of 1984 contained a plastic reservoir MC. I fitted it to my Cooper S. The original MC that came out of my S is presently on my woody.

Mur , I know I have read what I told you about BL going to a larger volume master cylinder because the extra force on the friction martial on Cooper S’s with vacuum assist causes the friction material to wear away quicker, thus lowering the volume in the resavoir quicker. Engineers were afraid that drivers wouldn’t keep close eye on this. I will post this for you when I find it, but not today ,as I’m tired and off to bed. Cheers, Darren

——smugness is a disease ——-

Thank-you Mur. What a breath of fresh air. Cheers.

Metal reservoir master cylinders don’t cause rust. Moisture absorbed by brake fluid causes rust.

Larger volume master cylinder reservoirs are just that, the same bore but with a larger reservoir, so those who neglect their car can completely wear out the linings. There is no extra force, there is no need nor is there ability to displace more fluid with every brake application.

Metal looks nice. Plastic looks nice also.

Hi cpear. Aside from being rustproof, the newer plastic brake master cylinder reservoir holds more brake fluid. This is of some importance because when you upgrade your brakes, you will very likely need to displace more brake fluid for every application. This may seem insignificant, but it isn’t. BL went with a larger capacity master brake cylinder with a larger reservoir when the Cooper S was introduced because the extra force placed on the brake friction surfaces caused the pads and shoes to wear quicker. This quicker wear would have ment more frequent topping-up of the reservoir if they didn’t increase the reservoir capacity. The only other factor is looks, and you are looking for performance, not concours, so I suggest the larger, plastic reservoirs M C. Added plus - no rust entering from the bean can.

Cheers and good luck with your project. Derwood.

I have the plastic for both brake and clutch, the cover on the clutch reservoir got cracked and eventually fall off due to the chemical reaction brought about by the brake fluid.  Thats one of the downside of using a plastic . 
But id rather use plastic than being called a purist for using a bean can. Plus, the bean can does not look good inside my engine bay, my girlfriend said it looks like a can of evaporated milk without the label.

Right now your car has a single line brake system. If you have a serious leak anywhere the whole system can fail. Not too likely if you keep up with things. When you upgrade power levels it might be a good time to upgrade to a split system. The only master for that is plastic. Otherwise it makes no difference other than looks really.

I am in need of new MC for both brake and clutch, is there any benefit (other then price) in going with the new style plastic ones? I currently have Bean Cans on my 65 Traveller and both need to be replaced.  I will eventually be moving to a 1350CC engine (currently original) and moving to disc breaks.

Thanks for the help and insight.

-c

1965 Mini Traveller.