Brakes

The brakes of a Gemini are designed to decelerate the mass of the car, and anything the car might be transporting, such as passengers and luggage in the boot. The intended environment of this braking is on highways or city roads, where frequent aggressive stops from high speed don't happen.

Due to these requirements, the manufacturers have found that a small solid disk brake and twin piston caliper on the front, and a drum brake on the rear are sufficient. And they are right, if you do not exceed the speed limit, and if that is the only type of braking that you want to do.

During a braking even, the vehicle lurches forward on its suspension and more of the vehicles weight is transferred to the front tyres, and obviously the load on the rear tyres is reduced. Because of this, the front brakes are made to work harder than the rears. The fronts might typically do 70% of the braking, therefore the rears would do the reaming 30% of the braking work.

Brake fade is the result of certain braking components overheating, and becoming ineffective. These components on a Gemini are the front disks and pads, the brake fluid, and the rear drums and brake shoes. Factory equipment will overheat if used for other than their intended use. If you continually use the standard Gemini brakes to slow you down with only short periods in between braking actions, there won't be enough time to allow the brakes to cool down. The temperatures will continue to rise until the brakes become ineffective. This is brake fade. Read the description below:

BRAKE FADE

Standard Gemini front solid rotors do a good job of pulling up the car at a set of traffic lights, but as soon as you attempt any form of performance orientated driving, you will notice that the standard brakes begin to fade. This is due to the heat generated from the friction between the brake pad and the rotor. The heat cannot be dissipated as quickly as it is generated and absorbed.

The result is a reduction in the amount of friction available between the pad and rotor, and it is this friction that actually does the braking. Thus, reduced friction = reduced braking performance.

The more braking you do without ample time to allow the components to cool, the worse the performance gets. You can push as hard as you like on the brake pedal, but the brakes simply cannot generate any more friction due to being overheated.

This heat will travel too, overheating other components and damaging them or shortening their life. This is especially the case with brake fluid, which can boil. When a liquid boils, it is being converted to a gas. Gas is compressible, whereas liquid is not. So the normally solid brake pedal which is pushing on liquid brake fluid is now trying to push on a gas. Instead of this gas working like a liquid, it compresses and the brake pedal can simply go to the floor, without barely actuating the vehicles brakes. Definitely a scary feeling when approaching a corner after doing 200+ km/h down the strait. After pumping the pedal several times, the gas compresses to a point where it starts operating the brake caliper pistons, but not as effectively as a pure hydraulic system with no gas present.

Brake fade is especially an issue if you have a Gemini with power levels higher than standard. If racing, you will approach corners with a higher vehicle speed, thus requiring the braking system to absorb and dissipate a higher level of heat than a car travelling slower. Also not only do you approach at higher speeds, you also navigate through corners more often because you are travelling faster around the race track for example. This means there is less time between brake applications for the brake components to cool sufficiently for correct operation.

Drums are renowned for brake fade, but as they are only used on the rear of the Gemini, and as the rear does about 30% of the work under hard braking due to the weight transfer to the front of the vehicle as it lurches forward. Because of this, fade on the rear of a car is generally not as big of a problem, but for a Gemini with drums, it does happen. I am not aware of any type of performance brake show that is available off the shelf either. The solution is a conversion to a disk brake rear end. Drums also go out of adjustment pretty quickly when racing, and this gives a similar pedal feel to faded rear brakes. Drums are not race friendly because the don't self adjust.

I have done a fair bit of circuit racing with the standard drums on the rear and found that the rear brakes are out of adjustment after about 3 hot laps of a circuit and they keep getting worse, which results in the pedal going further and further to the floor before getting the same amount of deceleration. Disks will have the benefit of being self adjusting.

The solid disks as used on the front of the Gemini are also susceptible to brake fade due to their design and size and the fact that they do the majority of the cars braking. Disks in general are better at self cooling due the the availability of airflow over the disk during forward motion of the car. Solid disks and ventilated disks are available within the industry, solid disk being fitted the the front of the Gemini.

Ventilated disks will cool better than a solid disk as they are really two disks with air channels between them for further improved cooling.

The only time I can foresee any form of brake upgrade necessary is when more 'spirited' driving, or some form of racing is performed. Another thing to note is that an increase is rolling radius of the wheels/tyres has a direct relationship to a decrease in braking performance. In short, if you increase the rolling radius of your tyres, you will actually loose brake performance. Its much the same as having a big or a small diameter brake rotor. If you have a large diameter rotor, you can clamp it with a caliper and stop it spinning more easily than if you have a small diameter rotor. Its the same for tyre size, where you could think of the road as trying to push the contact patch of the tyre and make is spin. The bigger the tyre, the easier it is to make it spin if the road is pushing it. The road has more leverage on a bigger tyre than on a smaller diameter tyre. Therefore a bigger tyre needs more braking effort to pull up the same mass over the same amount of time.

For drag cars, I have found good results with just a front pad upgrade to something like Bendix Ultimate pads, and the rest being standard brake hardware (providing the rear drums are adjusted correctly). Unless your car is doing some really quick times, with trap speeds over 110mph or so, then maybe you should look at a bigger disk for the front, or maybe a parachute. The reason I say this is because all drag racing tracks have sufficient runoffs to allow a car with cool brakes to come to a stop, but I have driven my Gemini fitted with completely standard brakes, coming to a stop from over 200km/h and experienced brake fade enough to get worried about. The Bendix Ultimate pads allowed a continuing level of deceleration after the factory pads would have overheated and performance faded.

Its when some form of hill climb or circuit racing is on the agenda that a ventilated disk for the front, and a disk for the rear might be needed. If you have a low horsepower engine, then a brake pad upgrade with standard brake hardware may prove sufficient due to the longer times between corners, compared to quicker cars. Vehicle weight must also be taken into account, as the heavier the car, the harder the brakes have to work, and more heat is generated, promoting brake fade.

If you do end up experiencing brake fade, check out my for sale page as I have a few different options you could try.