The brake system layout on the early 924 versus the 83-and-later 944 variants, including the 924S and the 968, are very different. This short article will explain the differences and help answer any questions that you may have, particularly those of you wanting to update your early 924 to 944 4-wheel disc brakes.
All cars in this series use a dual zone braking system. The idea here is that with two separate systems, when one fails the other can at least stop the car without using the emergency brake system. This is a great safety feature, but manufacturers were left to figure out the best way to execute the concept.
With the initial design of the 924, the two zones were split diagonally, meaning that the right front and left rear were on one system while the left front and right rear were on the other. This was common at the time, and braking systems of the time adapted well to this diagonal split. The master cylinder had two equal-sized chambers so everything was equal between the two. Remember too that these cars had disc front brakes and drum rear brakes. (I have never personally lost one of the two systems while driving, so I cannot say what half-braking is like. It could not have been fun, though!)
One of the drawbacks to this system is that there is no way to proportion the brakes front-to-rear – adjust the amount of brake force to the rear to adjust the braking characteristics of the car. This problem was solved with the 944 when the braking system was redesigned to split front-and-rear. Engineers could then modify the master cylinder to apply the proper braking pressure to each end, and the addition of a proportioning valve could then provide more adjustability. As the model matured, different proportioning valves were added to further customize the brake behaviors to meet the needs of that particular model, caliper and rotor size, weight, etc.
I have heard from plenty of folks with early 924 cars who want to go to the 924T or 944 five-lug wheels and four-wheel disc brakes. Our 924 ITB race car has four wheel disc brakes from a 924S (yes, it’s legal) and a 924S master cylinder. However, the original car was plumbed as a diagonal system, so the brake system had to be completely refitted with new lines going to the right places. I also added a proportioning valve to the system so that I could adjust the brake behavior front-to-rear, and placed that valve in the interior next to the shifter. I ran the brake line along the tunnel inside the car instead of underneath.
In the 944 front-and-rear system, the rear brakes are fed from a line that goes from the master cylinder, across the back of the engine bay, under the car on the passenger side to a three-way juncture in front of the rear axle. There it splits to each of the rear wheels.
In the front, each wheel is fed from a separate line from the master cylinder. The left wheel line is an easy route, while the right front goes across the engine bay at the firewall and goes forward to the wheel.
Here are some tips to proper brake maintenance:
- Change your brake fluid often. Here in the south, we have a humid environment, and brake fluid does not react well to moisture. As the moisture content rises, boiling point lowers. Get the brakes hot and you lose them.
- When bleeding brakes, do not use a partner to pump the brake pedal. Instead, get a vacuum bleeder or a pressure bleeder and leave the pedal alone. When pumping the brakes to bleed them, you are pushing the seals in the master cylinder past where they normally go and possibly into areas that have some surface corrosion. This can damage the seals cause premature failure of the master cylinder. Have you ever bled the brakes only to have a master cylinder failure within a few weeks or months? It was your fault.
- When replacing pads, replace the rotors. They are relatively inexpensive and will improve the function of the new pads.
There are two concerns with brakes on your 944 or 924S. The first concern is that for some time now there has been a shortage on the market for rebuilt rear brake calipers for the 944. The principle rebuilt vendor worldwide has been A-1 Cardone, and they are almost always out of stock, so no one has them. Rebuild kits are available, but rebuilt calipers are not. Fronts are also becoming an hit-and-miss issue.
The second is that the aftermarket hardware kits for your calipers are no longer available, so the only source is your local Porsche dealer. The price for the kit, containing the two rods that hold the pads, the four-sided spring and the retainer clips for the rods, is about $70. Too much in my book, so take care of the hardware when you disassemble the caliper or change pads.
We tend to think about power and handling, but since the stock brakes on a 944 are so good, we tend to neglect them. Give them a little love, and you’ll stop better because of it.