Over 5 million Minis have been made, most of them before 1985 when front disc brakes were standardised. Previously, standard Minis were fitted with drum brakes all round, adequate in light traffic but prone to fall out of adjustment
More importantly, the drum brakes are not capable of safely stopping a Mini that has been fitted with a more powerful engine
Mini brake systems
First, a summary of Mini brakes through the years (the major different versions are in bold):
1959 - 1964 Drums all-round, with single leading shoes - only one hydraulic cylinder in each front drum. These brakes can barely stop the original 848cc M
1964 - 1985 Twin leading shoe drums fitted to the front wheels - two hydraulic cylinders per side. Minis post-mid
1970s fitted with tandem brake circuits.
1961 - 1964 Mini Cooper 997cc fitted with 7 inch disc brakes. Barely as effective as twin leading shoe drums, and more prone to fade. Rather dangerous.
1964 - 1969 Mini Cooper 998cc fitted with 7 inch disc brakes, calipers redesigned with larger brake pads. Same problems as original design, not dangerous but still inadequate. These calipers were also fitted to later 997cc Coopers.
1963 - 1971 Mini Cooper S fitted with 7.5 inch disc brakes, ventilated wheel rims. Larger pad-disc contact area, 80% improved cooling efficiency and a brake servo give this configuration serious stopping power. The definitive Mini brake setup since it fits under 10 inch wheels.
1970 - 1974 Early 1275GT models with 10 inch wheels fitted with the Cooper S setup.
1974 - 1979 Mini 1275GT fitted with 12 inch wheels, needed to accomodate non-servo 8.4 inch disc setup. Later GTs fitted with twin-circuit braking system.
1985 - present All Minis fitted with later Mini 1275GT setup, above. Servo fitted from some time in 1989.
Improving your brakes
Any old Mini braking system can be improved by moving to one from a later year - Mk1 Minis with single leading shoe brakes can be converted to twin leading shoe without sacrificing the looks of the car but the conversion most people are interested in is "Drums to Discs", improving your Mini's stopping power.
Note that all Mini disc brake hubs from the original 997cc Cooper to present are apparently the same, or at least fully compatible.
Here is a guide to brake swaps:
Conversion Comment Method
Single Leading Shoe (early Mk1) to Twin Leading Shoe Cheap, effective, retains original look. Swap front brake backplates and all attached brake components with those of a twin leading shoe car.
Drums to Cooper S Discs Expensive, highly effective, very common, all parts available new including hubs, retains 10 inch wheels. Widens the track of the car. Swap complete hub assemblies for Cooper S hubs. Note steering arms are different between Mk1 and Mk2-on cars - use arms that match your car. Cooper S steering arms are uprated but not necessary.
Swap CV joints and stub axles for those from any disc brake Mini.
Swap to Cooper S driveshafts and Hardy Spicer inner joints recommended.
Swap Master Cylinder for Cooper S type.
Swap Brake Balance Valve for Cooper S type.
Fit disc brake Mini rear drums with built-in spacer and longer wheel studs.
Fit Cooper S rear slave cylinders and shoes.
Fit disc brake Mini front flexible brake lines.
Optional: Replace ball bearings in rear hubs with (stronger) Timken taper roller bearings.
Cooper to Cooper S discs Effective increase in stopping power, car looks unaltered. Fit Cooper S backplate, drive flange, caliper, and disc to Cooper hubs.
Drums to 8.4 inch discs Cheaper than S discs due to use on post'85 Mini. Fit all parts as specified for "Drums to Cooper S discs", but from 1275GT or post-'85 Mini instead. If using single-circuit brakes, fit a single-circuit 1275GT master cylinder and brake balance valve. If the car has dual-circuit brakes, there is no need to change the master cylinder.
Fit 12/13 inch wheels.
Drums/Discs to vented 4-pot Metro setup. Increases braking power. Braking may be excessive if the car is light (e.g. stripped for racing). From drums, "follow Drums to 8.4 inch discs".
Fit backplate, caliper, drive flange, CV/stub axle, vented disc to Mini disc hub.
Fit "Metro Disc Brake Conversion Pipe Kit", required since Metro calipers have two hydraulic connections.
The complete 4 pot setup may be purchased as a conversion kit from various Mini suppliers.
From Cooper S discs, fit 12/13 inch wheels.
Some wheel rims may not fit unless the wheel locating lugs on the Metro drive flanges are machined off.
For twin circuit systems, fit a current-spec Mini servo.
Metro brakes and safety notes
Metro 4-pot brake system drive flanges feature wheel locating lugs. These can obscure access to the castellated hub nut or prevent some wheels from fitting as noted above, in which case the locating lugs may be machined off, any engineering works or engine reconditioner will be able to do this. This is evidentley not a major problem.
Metro alloy wheels will fit on a Mini. However, they are offset towards the center of the car compared to Mini wheels, narrowing the wheel track and causing potential problems Fitting of Metro alloy wheels is not recommended.
Always use Mini Disc Brake Hubs.
The extra cost over Metro hubs is not worth risking the life of yourself and others over.
Also, many people have converted from drums to discs without any of the specified modifications to the hydraulic system. This appears to work from day to day, but the brakes will be unbalanced between front and rear, the track will be wider at the front than the rear, and the master cylinder's bore is different and it holds less fluid. What happens when you really have to rely on the car's handling, or the discs are worn causing the pistons to move out, absorbing all the brake fluid from the master cylinder?
Never attempt to save money or effort on brakes.
Your life and the life of other road users depends on the reliability of your brakes.
Apologies if the above notices sound condescending, but lives ARE at stake
Vented/4-Pot brakes and 10 inch wheels
Many people desire the combination of 4-pot vented Metro brakes and ten inch wheels. The Metro disc setup will not fit under ten inch wheels. It is possible to adapt the setup to fit; this involves turning down the brake discs from 8.4 in to 7.9 in, machining metal off the caliper, and re-drilling the caliper mounting holes in the hub.
The last two operations above are not safe, and the overwhelming majority of specialist advise against this option. Due to production tolerances in the caliper castings, no-one knows exactly how much metal will be left on the caliper to dissapate heat and keep the fluid in, and it takes considerable expertise to safely modify castings such as the wheel hubs. Don't take this option.
If you truly want vented 4-pot brakes under ten inch wheels, buy a set of alloy calipers from Mini Spares or Mini Sport.
Use the driveshafts that are fitted to your Mini, of if you prefer, upgrade to pot-joint or Hardy-Spicer driveshafts, or thicker Cooper S or Special Tuning driveshafts for mre demanding uses. Metro driveshafts are too long and will not fit.
Choosing a brake setup
There are a number of alternative brake setups, and some are more appropriate than others for certain circumstances:
Single leading shoe drum brakes are suitable only for originality and do not provide sufficient braking for the requirements of modern traffic, even with an 850cc engine.
Twin leading shoe drum brakes are suitable only for 850cc to 1100cc Minis and may be considered barely adequate.
7 inch discs should be retained only for originality, as they have barely the same stopping power as twin leading shoe drums.
7.5 inch discs are optimal for 10 inch wheels, but the increased rotational inertia of 12 and 13 inch wheels can reduce their effectiveness. This setup is suitable for highly tuned Minis.
8.4 inch discs (non vented) are suitable for 12 or 13 inch wheels and are less expensive than 7.5 inch discs. This setup is also suitable for highly tuned Minis.
8.4 inch discs (vented) with 4-pot calipers are only necessary for high speed driving, or driving with heavy and repeated braking or where brake fade has been experiences with the non-vented 8.4 inch setup. The increased heat dissapation capability of this setup may prevent some uprated brake pads from reaching an ideal operating temperature.
4 pot calipers may be added to 7.5 and 8.4 inch non-vented disc setups and provide a worthwhile increase in pad-disc contact. Metro 4 pot calipers for 8.4 inch wheels are much cheaper than the custom billet alloy calipers specially made for 7.5 inch setups.
Beyond Standard Brake Setups
The only car that has any degree bolt-on brake compatibility with the Mini is the Metro. Brakes from the Austin 1100/1300, MG Midget and other BMC cars will not fit - many are of the same conceptual design but the sizes, shapes and angles of the hubs, calipers and discs are wrong.
As noted in the table above, it is safe to fit Metro vented discs, flanges and calipers to Mini hubs. This is the ultimate road going setup. If you demand more, for "pose value" or for racing, the following setups are available from some Mini parts retailers at relatively great expense:
Alloy front hubs and rear trailing arms, rear disc brakes (non road legal due to lack of handbrake), and 6-pot calipers are available from KAD.
4-pot alloy calipers are available from Mini Spares, Mini Sport and others, for vented, non-vented 7.5inch and 8.4 inch disc setups.
Custom rear-disc conversions are available from some Mini specialists in the UK.
Adjustable brake bias valves and alternative master cylinders are available for racers. Some also use one-off designs featuring discs and calipers from other cars.
Hope this helps cheers Dean