23 replies to this topic

[TimNeal]

Hi , I'm having an issue with my brakes
4 pot mini sport calipers
Pedal travel stops 2cm off the floor, brakes are operating but with out bite.
It's got newish pads & rotors.
I was reading on Mini sport website that there's a Cooper S specific master cylinder, same bore but taller by 15mm
With increased fluid capacity , so I assume (???) longer stroke meaning more "umph" in the system

Any advice to offer ?

[sonscar]

Pedal stroke is affected by relative diameters of pistons and cylinders relative to master cylinder bore,assuming adjustment and pad clearance is correct.This relationship also affects brake pressure.Larger volume of fluid will not help.Steve..

[mab01uk]

The increased fluid capacity of the taller Cooper S/1275GT master cylinder was introduced because the brake fluid level can drop more quickly below minimum, with disc brakes as the brake pads wear, than it does with the earlier Minis drum brakes/brake shoes. If the brake fluid level dropped below the minimum level between checks/services air could enter the braking system...

Edited by mab01uk, 17 September 2026 - 09:42 AM.

[Ethel]

If the pedal hasn't hit the floor a bigger reservoir won't help. The first thing that happens when you press the pedal is the piston passes the port connecting the cylinder to the reservoir so the fluid can't escape & has to transfer pressure to the calipers. A larger reservoir means a bigger reserve for when the pads wear down and the pistons move out creating more volume in the cylinders behind them.

 

Things to check:

 

Are the rear brakes adjusted & rear wheel cylinders not leaking?

Do your front wheel bearings have any play that's allowing the discs to wobble & push back the pistons?

Is there damp around or under the dust boot on the cylinder above the brake pedal, suggesting a leaky mastercylinder?

 

The front brakes do nearly all the stopping. If you can get a hard, not spongy,  pedal (travel doesn't matter) & assuming the pistons aren't seized in the calipers, it could well be the condition of the discs, pad compound being too hard or possibly contamination of the friction surfaces. 

[stuart bowes]

what brake pads are you using (Ref 'operating but without bite')

 

pedal travel, no idea, see other's comments  ⬇

Edited by stuart bowes, 21 September 2026 - 01:39 PM.

[Spider]

They were never a good caliper, but, if they are new, the seals will be dry and so the pistons in them won't be self adjusting as they should. Remove 1 pad, chock 1 piston of the 2 exposed, pump the pedal about 4 - 5 times to move it out about 1/4", push it back in and move on to the next, doing all 8 pistons, This will lubricate them and you'll likely find the pedal will be higher.

[Ethel]

We are assuming it's a single circuit setup, since you mentioned the Cooper master cylinder. If it's dual circuit a circuit may be out, leaking or just in need of bleeding. Spider could well be right about the poor performance, but I don't think it'd cause the excess pedal travel.

[Lplus]

Hi , I'm having an issue with my brakes
4 pot mini sport calipers
Pedal travel stops 2cm off the floor, brakes are operating but with out bite.
It's got newish pads & rotors.
I was reading on Mini sport website that there's a Cooper S specific master cylinder, same bore but taller by 15mm
With increased fluid capacity , so I assume (???) longer stroke meaning more "umph" in the system

Any advice to offer ?

What size disc?

Did you have standard calipers before and is there any improvement at all?

 

Personally, I have put minisport 4 pots on 7.5 discs and they were an improvement on standard S calipers, but not a huge amount.  Fitting a servo improved them no end and they're almost up to modern car feel now.

I also have a set of S discs and calipers on another mini and they definitely needed a servo.

[nicklouse]

Hi , I'm having an issue with my brakes
4 pot mini sport calipers
Pedal travel stops 2cm off the floor, brakes are operating but with out bite.
It's got newish pads & rotors.
I was reading on Mini sport website that there's a Cooper S specific master cylinder, same bore but taller by 15mm
With increased fluid capacity , so I assume (???) longer stroke meaning more "umph" in the system

Any advice to offer ?

Your assumption is incorrect. The volume is only there for pad wear in extreme situations. Like is says increased capacity. The stroke is the same.

 

so back to the problem. Poor pads? You don’t say. Poor rotors? you don’t say. Poor installation. No images.

 

But the calipers aren’t the best they do flex.

[Midas Mk1]

In terms of blaming the calipers, i’ve had 4 sets of Minisport 4pots now and have got a decent nice pedal on all of them, done many of thousands of miles with them.

As above, check rear brake adjustment, pressure bleed if needed to ensure no air in system. Then it’ll be checking master cylinder, bulkhead bias valve if you have one, had both of those start to fail on me in the past.

Check flexis are in great condition, not ballooning too.

Edited by Midas Mk1, 20 September 2026 - 07:39 PM.

[coopertaz]

what circuit are you running and is a servo fitted. these calipers on the later split system with a servo and standard pads (7.9 inch discs) are similar to standard 8.4 inch units. if you run any disc without a servo you get a hard feel to the pedal and the only solution is to fit a servo or press like hell! my other car with non servo 7.5 cooper s is like this.

[nicklouse]

Have a read though this about brakes.

https://www.calverst...-how-they-work/

[stuart bowes]

holy cosmic bullsh.t, batman!

 

SPAM ALERT lol

Edited by stuart bowes, 21 September 2026 - 08:01 PM.

[Gaz66]

Block the spammer 👍🏻

[Spider]

Thanks everyone, the Spam has been dealt with