The Low Down On Brakes!
Posted 23 January 2008 - 03:23 PM
Table of Contents
Standard Brakes (Drums and 8.4" discs)
Standard Upgrades (Cooper, Cooper S and Metro/ERA Turbo)
Modified Standard Items (Spacers and Grinding)
Fiesta Caliper Conversion
Aftermarket Options (Alloy 4 and 6 pots)
Extra Options (MRA, Tarox, Wilwood and KAD Rear Disc)
Posted 23 January 2008 - 03:27 PM
On a standard Mini, drum brakes can give you as much stopping power as disc brakes. In fact the contact area between the pad (or shoe as its called with drum brakes) and the friction surfrace of the drum far exceeds the contact patch on any disc brake setup currently available for the Mini. Unfortunately the force behind the pad (or shoe) pushing it against the friction surface around the drum is a bit lacking. When properly maintained and regularly adjusted, drum brakes can be very effective on any standard Mini. The problem with them is that they don't dissipate heat as well as disc brakes, so when you begin to brake several times from high speeds, the brakes soak the heat, and then you get problems with brake fade; the brake pedal will become spongy and the brakes will become more and more ineffective. One option to get around this is to fit 'Superfins', which are pretty much standard brake drums but with many cooling fins added to the outside. These fins increase the surface area of the drum and so (along with the fact that they are made from Aluminium) help to dissipate the heat caused by repeated high speed braking and help to stave off brake fade.
(Standard rear drum brake)
NB: It has come to our attention that there are some cheap copies of Superfins floating around the Mini scene. These often do not have the Steel band friction surface inserted. Without this friction surface the brake shoe will eat through the Aluminium drum pretty quickly. These cheap copies are very dangerous. Always look for the Steel insert which should appear as a different colour to the Aluminium.
8.4" Disc brakes.
In April 1984 disc brakes became standard on all new Minis. The 2 pot cast Iron caliper from AP is very good, and generates more than enough stopping power for the weight of a Mini! Its only once you start getting some laps in at a track day that you'll start to find you get brake fade, and even then this can usually be overcome by fitting some fast road, or track orientated pads. These brakes generally only fit under 12" wheels. If your converting from drum brakes to this brake setup you'll need disc brake CVs, hubs, driveshafts and disc flanges, along with the obvious calipers, discs and pads! Complete assemblies can usually be found in autojumble at shows for roughly £50 a pair, however I'd always advise budgeting for refurbishing them; renewing balljoints, wheel bearings, CV joints, discs and pads, and perhaps even rebuilding the calipers, and painting the hubs, calipers and drive flanges if you so wish.
(Standard 8.4" disc brake setup)
NB: With all standard disc brakes, they increased the track at the front by 1". To correct this at the back, a 1" spacer was used, usually built into the drum, along with longer wheel studs.
Posted 23 January 2008 - 03:31 PM
7" - Mini Cooper
1960s Mini Coopers were fitted with 7" disc brakes as an upgrade to the drum brakes Minis had at the time. Unless your going anal about a restoration of a Mini Cooper my advice is to stay away from these disc brakes. The pad area is tiny and they offer little braking power. In fact most people say they offer worse braking performance than the drum brakes they replaced!!
7.5" - Mini Cooper S
Unlike the 7" disc brakes fitted to Mini Coopers, the Mini Cooper S (again the 1960s version) got the slightly larger 7.5" disc brake. Now you wouldn't have thought the extra 1/2" would make that much difference, but you'd be wrong! The caliper piston is further out (increasing the braking leverage) and the pad area is bigger. The braking performance from these brakes is very good, comparable with that from 8.4" brakes. Again you shouldn't get any brake fade from these (using decent road pads) unless your really pushing them, probably on a track, and again this can usually be eliminated by fitting fast road pads. When the Clubman 1275GT first came out, it was fitted with these 7.5" brakes, this was then changed in 1975/76 to 8.4" brakes. Complete assemblies, sometimes with driveshafts (if converting from drum brakes) can usually be found at shows for roughly £250, alternatively Mini spares sell these conversion kits; Full conversion kit including hubs and CVs, or Conversion kit using existing hubs.
(Cooper S discs with drive flanges and calipers)
Its worth mentioning that the Cooper S disc is different to the later 8.4" disc. The Cooper S disc has integrated wheel studs, which the drive flange then sits over and bolts to, because of this you cannot fit longer wheel studs when using the Cooper S 7.5" brake setup, and therefore cannot safely use wheel spacers. On later 8.4" discs the wheel studs are driven into the drive flange and are an interference fit, so can be changed quite easily.
Metro/ERA Turbo vented 4 pots
One more option of utilising standard calipers is to find the brake setup from a Metro Turbo. Instead of having two pistons pushing the pad onto the disc, these calipers have four slightly smaller pistons, which sit further out towards the edge of the disc. Overall this gives you more force pushing the pad on to the disc, which results in better braking performance. In addition to these two extra pistons per caliper, the discs used with this setup are of the vented variety. Being vented the surface area of the disc is greatly increased meaning that heat can dissipate away from the disc quicker and easier, which results in less chance of brake fade when your really pushing your car to its limits.
To use Metro Turbo brakes on your Mini you'll need to retain the standard Mini hubs, but use the Metro/ERA Turbo calipers (obviously), drive flanges and disc and pads (makes sense to renew them when converting though). The first difference is that each caliper needs two brake hoses, compared to one brake hose used on standard Mini calipers. A number of companies, including Goodridge, make conversion hose kits for exactly this conversion (Link). The other difference is that the mounting lugs on the Metro caliper have a larger diameter hole than those on the Mini caliper. If you used the standard Mini caliper bolt with the Metro caliper, the caliper is able to move about, which as you can imagine is very dangerous. To overcome this problem you need to use the ERA Turbo caliper mounting bolts, which have a metric shank, but the normal Mini imperial thread (Link).
(Vented 4 pot disc brakes as fitted to the ERA Turbo and Metro Turbo)
Posted 23 January 2008 - 03:34 PM
It is possible to use 10" wheels over standard 8.4" discs brakes. Certainly with 10x6" Weller wheels you can use an additional 1" spacer to space the disc outside of the wheel. This then gives you enough clearance to use the 8.4" caliper. This then also requires you to add an additional 1" spacer to the rear drums as well. This now means that the wheels will be spacered out 2" more than originally intended, which will put more strain on the wheel bearings and balljoints. This generally isn't a problem with small 10" wheels which are relatively light, but just know that the wheel bearings and balljoints *might* not last as long as they should. Please also note that the spacer kits with the scew on stud extensions are BAD! The idea is incredibly dangerous, and I plead to anyone who is thinking about adding spacers to buy the extra long studs.
(KAD Alloy caliper with spacer)
Grinding the Caliper
The other option to use 10" wheels over the standard 8.4" brakes is to grind the caliper slightly. Now most people will recoil in horror at the thought of grinding calipers, especially since there can be differences between each casting. The amount of grinding required is on each corner of the caliper, enough to give you between 3-5mm clearance between all parts of the caliper and the wheel. Its recommended that you get a spare pair of calipers if you wish to go down this route, and grind them until you break through into the fluid ways. This will then give you a good idea of how much metal you can and can't remove before the caliper would become dangerous. Even after doing this, and grinding the calipers you plan to use, I would also recommend you take the calipers to an engineering firm to get them pressure and crack tested. Ensuring everything is honky dorey, this will at least give you a clear conscious knowing that your calipers aren't going to fail on you. For a more in depth look at this conversion click here.
(A standard 8.4" caliper thats been ground to give clearance on a 10" wheel)
Posted 23 January 2008 - 03:35 PM
This is a conversion using the MkII Fiesta caliper that has only recently become quite popular for anyone wanting to fit 10" wheels over disc brakes. The main advantages of this conversion is that it is relatively cheap compared to Cooper S conversions, and alloy 4 pot calipers; the conversion can usually be carried out for roughly £75-£150. Compare that to the Cooper S setups which can cost upwards of £250, and alloy 4 pot calipers which are upwards of £300. One thing to note is that these calipers are still cast iron items, using 2 pots (pistons), therefore you won't generally experience any increase in braking performance over the standard Mini 2 pot caliper. The conversion is quite easy to do, especially if you have a pillar drill and a grinder, but even using an engineering company to perform a couple of the modifications required won't end up braking the bank. I won't go into all the details involved in fitting the Fiesta MkII calipers, as there is a great video done by TMF and Mini Addicts members MarkRally and Gr4h4m - Link.
Posted 23 January 2008 - 03:39 PM
Alloy 4 pots
The aftermarket options are pretty much limited to just alloy 4 pot calipers. The advantage of having 4 pots/pistons, as I've said with the Metro Turbo calipers is that you then have more force pushing the pad against the disc. You then have the added benefits of the caliper being hewn from a solid block of alloy, which means the caliper is a lot lighter than standard cast Iron calipers and they also dissipate heat easier. Being lighter means you also lose weight from the unsprung mass, which helps to improve handling, and also goes some way to improve all round performance, and as mentioned before, being able to dissipate heat means you are less likely to suffer from brake fade. There are generally three options of alloy 4 pot caliper you can buy, those for 7.5" discs, those for 7.9" discs, and those for the standard 8.4" disc. Those for the 7.5" disc generally use the Cooper S disc, and so its worthwhile to note that you will need Cooper S drive flanges too, and that the wheel studs are built into the disc. The 7.9" and 8.4" caliper are both a direct replacement for the standard Mini caliper, and use standard Mini hubs, drive flanges, etc. The 7.9" disc is just a machined down 8.4" disc, so you can just buy 8.4" discs and have an engineering shop turn them down for you. Also worth noting is that the 7.9" and 8.4" calipers use Metro brake pads, and that you usually have to file the two inner corners off the pad. This does not remove any of the friction surface from the pad and does not compromise the structural integrity of the pad in any way. This option is the most expensive (£350-£500 for calipers with pads), but is generally thought to be the best all round solution. One more thing to note is that, as with the standard cast Iron 8.4" calipers, alloy 8.4" calipers WON'T fit under 10" wheels, unless you use a spacer.
(Alloy 4 pot caliper as sold by Mini spares)
Alloy 6 pots
Currently I believe the only company making a 6 pot caliper specifically for the Mini is KAD. These calipers have 6 pistons, as some of you quick people might have already worked out, so again more force to push the pad against the disc! These calipers don't use standard Mini pads either, they use a generic kit car pad, which has a much larger surface area than the standard Mini or Metro pad. So not only do you get more force pushing the pad against the disc, but you get greater friction between the two as a result of a larger contact area, which all goes into stopping you in double quick time. The other advantage of these specific calipers is that they are radial mounted. These means that instead of the caliper mounting bolts going into the hub perpendicular to the disc, the mounting bolts are parrellel to it (by way of an adapting box). This means that the caliper can then be mounted further in or out of the hub by using small spacers, so, if you wish to run 10" wheels you just need to turn the disc down to 8.2" or 8.3" and then adjust the caliper mounting spacers as necessary. You then also don't need to change to a different caliper if you say chose to change to a different wheel which requires more clearance, or even move to a 12" wheel which then means you can fit a much larger disc. However, these calipers are not supplied with any dust seals around the pistons and so these are race or track orientated items only.
(KAD 6 pot brake setup)
Posted 23 January 2008 - 03:40 PM
MRA Minis do several different kits of alloy calipers, and can sell you complete kits to give you the biggest possible disc to fit under any wheel you choose to place on your Mini.
Other companies that offer aftermarket alloy brake calipers of varying sizes include Tarox and Wilwood.
KAD Rear Disc conversion
Within this kit you are supplied with a pair of dual mechnical/hydraulic brake calipers, pads, drilled discs and Aluminium hubs. Its a very well developed kit, however some people make the mistake that it was developed to improve braking effort at the rear. This is not the case; as KAD's website says, the idea behind it is that it reduces weight. The rear disc kit weighs in at 2.8kg per corner, where as the lightest drum brake assembly is 4.6kg. So that represents a total weight saving of 3.6kg. At £673 you don't lose a huge amount of weight for your money, so you have to have very deep pockets, or have stuck your Mini on the 'Supermodel Bulimia' diet to warrant the puchase.
(KAD Rear Disc conversion kit)
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