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I have the large ventilated discs with alloy 4 pot calipers, in conjunction with the dual master cylinder (different bores top and bottom) and have never been happy with the braking of my Mini.

The pedal is always spongy, and requires alot of pressure to stop the car. The cylinder was piped with the smaller (top) piston to the front brakes, and the bottom (larger) cylinder to the rears. I also have a brake bias valve on the rear line.

I recently tried swapping master cylinder lines - now having the larger bottom cylinder operating the fronts. It is slightly better but still far from being good.

The car, a 1500 with 8 port head and electronic injection, is used for circuit racing.

Any ideas anyone?

Hi, i had a similar problem on my hillclimb car when i used a used the same system. I spoke to a guy in the tech dept at AP racing. He recommended fitting their smallest master cylinder (14mm) to the front circuit and leaving the 3/4 master cylinder with reducer in the rear line.
Having previously tried other cylinder sizes by trial and error this setup solved the problem.

Is yours fitted with a servo/power brake?

Mine is not.

John Bull wrote:Is yours fitted with a servo/power brake?

Mine is not.

Hi John, no just leg power. Also run Performance Friction 01 compound pad

As usual, I am going to be controversial, I think what you need is the sadly discontinued GMC167 dual circuit master cylinder, which provides a brake pedal which after half an inch of travel, feels like standing on a rock, it works fine with drums or big discs & 4-pots but I think it was unpopular because there was no way it would work standard 'S' discs & calipers without a servo in the front line. It was originally fitted to Minis with diagonally split hydraulic circuits, hence both sections were of the same bore diameter, but some Minis, such as mine were produced with the same master cylinder with a front to rear split. To my mind, there is no comparison between that & the soggy feel of the later one with different bore diameters.

Lord Croker wrote:
I think what you need is the sadly discontinued GMC167 dual circuit master cylinder

I've used these with these with 4 spots and are OK, definitely managable, though (and maybe I'm turning in to a pussy), I would probably prefer a slightly lighter pedal. I haven't done the sums, but I think to make the set up any lighter without a booster, you'd probably find the pedal going down a long way, so these ar possibly about as good as you'd get.

I do have a few NOS ones left.

Thanks all for your help.

I have one of the "parallel" old type twin master cylinders somewhere. I'll have to resurrect it and fit it and see what happens.

Rolling road Wednesday. Should be interesting

Lord Croker wrote:As usual, I am going to be controversial, I think what you need is the sadly discontinued GMC167 dual circuit master cylinder,

they have been re introduced. readily available from all good minispares shops