Braking system
From The Porsche 914 Wiki
Contents |
Introduction
The braking system on the 914 is a dual circuit hydraulic system with solid discs (rotors) on all wheels. The system is not power assisted, and the emergency brake is provided by means of a cable system connected to the actuator on the rear calipers.
(todo: insert diagram)
(todo: discuss general specifications of 914/4 and 914/6 braking components, sizes, etc. Include differences between early and late front calipers)
Maintenance
The stock brakes on the 914 are more than adequate to stop the car, provided all of the components of the system are well maintained.
(include specs/tolerances here)
Physics of Braking
The sole purpose of a braking system is to reduce the speed of a vehicle by converting it's kinetic energy (motion) into heat energy. This is achieved using friction between a brake pad and a steel rotor (the 914 uses disc brakes; other vehicles may use other methods, such as drum brakes, or regenerative braking).
The formula for friction is:
F = u N
where-
- u is the coefficient of friction (in this case the pad compound is the main variable)
- N is the normal force to the contact surface (how hard you hit the pedal)
- F is the maximum possible force exerted by friction (how much stopping force is being generated).
Note that the size of the brake pad has no effect on the braking force.
Upgrades
Since the 914 suspension (particularly the front) is based upon the design used by contemporary 911s, many brake upgrades are created by using parts from 911s and other Porsche models. Brake upgrades are a somewhat controversial topic. From a practicality point of view, the stock 914 braking system is quite adequate if properly maintained. If you are able to lock up your tires, then this means that your braking system has done it's best to stop the rotation of the wheels and that your overall braking ability is limited to the grip level of your tires and not the brake system itself. However, braking "feel" and fade resistance can be affected by braking system changes. Common upgrades are converting to vented rotors, larger calipers, different front/rear biasing controls, stainless steel brake lines and larger master cylinders. It is felt that those who are unhappy with their braking performance may have a problem with the stock system that needs to be corrected first before they decide that an upgrade is needed. 914s that are used on track or have significant engine upgrades are where brake upgrades provide the most praticle benefit.
Master Cylinder
(todo: Discuss master cylinder upgrades 19mm vs. 21mm)
Front/Rear Bias Control
(todo: Discuss stock bias adjuster, use of "T", other types of bias adjusters and when it is appropriate to use each type)
Front
Stock 914 struts use a 3" spacing on the ears that are used to mount the caliper to the strut. Early M-Calipers (todo: Create article about M-Calipers, S-Calipers, A-Calipers) which also have the same 3" spacing can be used. Later Porsche 911 calipers such as the S-Calipers and A-Calipers use a 3.5" spacing on the ears. To utilized these, the most straight forward way to accomplish this is to switch to 911 struts (todo: Create article about 911/914 front suspension) that use the larger spacing. Other Porsche models have also been used as a source for front brake upgrades. The front brakes from the Boxster have been used, but require an adapter to mount to the 911 or 914 strut.
(todo: Discuss BMW Ate upgrade option)
Rear
The rear brake on the 914 is just different enough from the 911 to prevent direct upgrades that provide all of the features that the stock rear brake provides. The main difference is that the 911 emergency brake utilizes a drum and shoe style brake that is incorporated within the rear rotor. While the 914 uses a mechanical system directly incorporated into design of the rear hydralic caliper. This difference makes the 914 and 914/6 rear calipers somewhat of a unique design. Upgrades that utilize 911 rear brakes generally result in either a loss of the use of the emergancy brake, or the need to perform additional modifications (todo: Create article on how to install 911 rear caliper on 914) to allow for the 911 emergancy brake to work with the 914. Other options are to use the 914/6 rear caliper as the upgrade for a 914/4. However the 914/6 rear caliper is extremely rare and are no longer available as a replacement part. Due to the cost, this option is usually not utilized. The use of a "spot caliper" (todo: Create article that defines what a spot caliper is) for emergancy brake purposes are occasionally used.
