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Have swapped to Cooper S discs/calipers/flexi etc.

Turns out the standard master cylinder is goosed so looking at fitting the Cooper S one. Not done this before. Any other parts I’m likely to need? Clevis pin etc?

Also, do I need to change the rear wheel cylinders to keep things balanced or fit a bias valve?

I’m not fussed about a servo if the above is acceptable...

You also may need the correct brake pedal, Cooper S, 1275 GT, or later Mini

A little search on the site will give more info, I have similar setup a change in Brake Pedal made a major differences

I thought the pedal was thicker but is there a change in the pedal pivot points ?

I think the S pedal is cranked slightly more so it sits a little higher.

Ah yes I’d forgotten about the pedal.

So the S ones are the same as later minis but with bigger foot pad?

Anyone got one for sale?

I dont think they're cranked as high as the dual circuit cars with the coffin shaped pad. I think that the S pedal became standard fitment on all the drum braked mk3's.

Ok I’ll try and locate one, if anyone has a spare please let me know.
Cheers

What about the rear wheel cylinders?

I'm using 5/8" ones on unservod 7.9" and KAD 4 pots but I think I had the same size cylinders on 7.5" S discs and calipers.

I’m guessing 5/8 are Cooper S ones not standard?

The only way to be certain is to measure what you've already got. Changing to different sizes cylinders may involve redrilling the back plates as the locating pins can be in different positions.

Ok thanks. I might just see how they behave as is and take it from there...

I've fitted an S Brake set up on many cars without swapping to a S Pedal. It's fine, though in use, the deal do go lower than would do if it had an S pedal, but not by a lot. Personally, I don't think that aspect is worth the agony of trying to find an S Pedal for. Now I think back, our Clubman GT, that was factory fitted with compete S braking system just had a standard pedal from the rest of the range.

docka wrote: ↑Wed Jul 08, 2020 8:56 am I’m guessing 5/8 are Cooper S ones not standard?

Most Drum Braked cars had 3/4" Rear Cylinders, were as the S had 5/8" Cylinders. You'd be wise to go to the smaller cylinders in the rear to stop them from locking up.

I'd agree with Spider regarding the S pedal.

I've got non servo'd S brakes on my 998 Cooper with a standard pedal and the brakes are fine.

The other option is to warm up the standard pedal (out of the car) and put a slightly bigger kink in it to raise it up, but its not really necessary.

Andrew1967 wrote: ↑Wed Jul 08, 2020 10:15 pm I'd agree with Spider regarding the S pedal.

I've got non servo'd S brakes on my 998 Cooper with a standard pedal and the brakes are fine...

Yep, I put non servo'd S brakes on my MK1 back in the '80s and I just used the original MK1 pedal and never had any problems either.

I changed my 63 with single leading shoes to S discs , it has a later plastic style (for now) master cylinder although the pedal is not spongy it is rather a long pedal travel . So thinking changing the rear cylinders to a smaller size would improve the pedal .
What’s the ideal master cylinder size with no servo for a S brake set up ?

roymck wrote: ↑Thu Jul 09, 2020 7:53 am I changed my 63 with single leading shoes to S discs , it has a later plastic style (for now) master cylinder although the pedal is not spongy it is rather a long pedal travel . So thinking changing the rear cylinders to a smaller size would improve the pedal .
What’s the ideal master cylinder size with no servo for a S brake set up ?

You'll likely have a 3/4" Cylinder in there now, but it could be a 5/8" too.

I think these days, you'll be a little hard pressed finding anything other then a 3/4" Master.

Ideal size ? Everyone's taste for how Brakes should feel is a little different, I don't mind the 3/4" Master without a Servo, but I'd like something a whisker smaller just to lighten the pedal up a little.

I would guess that a 998 cooper master cylinder at 0.625 bore would be ideal, I know on my 998 when I had a 0.7 master the brakes were not brilliant but as soon as I fitted a correct master things improved. The rear bias valve is also different For 0.625 rear cylinders but not sure how much this effects anything.

I started off reading this worrying about my (non-S) pedal, but I feel ok again now

Many years ago, I bought a Mk2 that had S discs and 0.75 rear wheel cylinders. It would lock the rears as soon as you looked at the pedal. This was, erm, entertaining for about 5 minutes, so I swapped to 0.625s and all was good.

One option I've seen recommended is 0.75s and the MS72 adjustable rear limiting valve, but I would actually be a little wary of this - I currently have an MS72 and 0.625s and I'm pretty near the end of the adjustment for road use to avoid locking the rears. With 0.75s I'm not sure it would go far enough.

Daz1968 wrote: ↑Thu Jul 09, 2020 8:42 am I would guess that a 998 cooper master cylinder at 0.625 bore would be ideal, I know on my 998 when I had a 0.7 master the brakes were not brilliant but as soon as I fitted a correct master things improved. The rear bias valve is also different For 0.625 rear cylinders but not sure how much this effects anything.

So retain the 3/4 rear cylinders and fit a 0.625” bore master cylinder Daz1968?

Any other opinions welcome, really appreciate the ideas and hoping I only have to change the master cylinder once if I get this right!