Heinkel Brake System- Inspecting and Testing

After riding in another Heinkel with excellent stopping power, and surviving a harrowing malfunction (entirely of my own doing) I decided to spend some time thoroughly inspecting and overhauling my brakes. What follows is my five-part series on how to inspect and overhaul your front brake system.
Heinkel Cars and Cabin Scooters
A Heinkel Master Brake Cylinder (with car parts attached!)

Part 1: Test and Inspect
Part 2: Wheel Cylinder
Part 3: Master Cylinder
Part 4: Reassembly
Part 5: Adjustment and Maintenance

Heinkel and Trojan Cars have a two wheel hydraulic braking system. The front wheels are used for primary braking. The rear wheel (or wheels) has a cable-actuated emergency/ parking brake. The brakes are considered one of Heinkel’s best features- when they are operating properly.

Part 1: Test and Inspect
Here’s a straightforward test: When you step on the brakes does the car stop quickly and precisely? Can you lock up both front brakes on a hard stop? If not, it’s time to dig in a little bit. If you accept the Heinkel’s acceleration as status quo for your car’s other systems, then you may not know how bad your brakes are.  I was used to the mechanical brakes of the Heinkel scooter, so again the car’s braking performance (or lack thereof) didn’t raise a red flag. In reality, properly operating Heinkel brakes approach the quality of modern brakes if your car is properly set up.
I didn’t know much about braking systems before I started working on the Heinkel. At the risk of boring the more experienced readers we’ll start at the beginning.

How Brake systems work:
As mentioned earlier the Heinkel has both mechanical and hydraulic brakes.
  • The emergency brake is mechanically operated. If you pull on the emergency brake, a cable turns a cam, which in turn pushes the brake shoes against the inside of the wheel hub, slowing or stopping the rear wheel.
  • The brake pedal pulls a piston in the master cylinder recessed into the floor of the car. The piston pushes fluid from a reservoir through a one way valve and then through brake lines into cylinders mounted on backing plates on each wheel. The fluid pushes pistons in these “slave” cylinders which in turn expand the brake shoes to press against a metal braking surface inside each hub.

If air gets into the brake system the brake performance will degrade significantly. That is the theory anyway. The brakes have relatively few parts, although there are key areas you need to pay attention to:
Leaks: These are pretty obvious. Look for tell tale leak signs. If fluid can leak out then air can get into your system. An easy way to check is to get a friend, press down and hold the pedal, and then see if the pedal drops. If the pedal drops because of a leak you’ll see it.
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Leaks typically drip onto wheel backing plate 
Typical leaking places are any areas where one part transitions to another. For example, drips on the wheel backing plate (leaking from the wheel cylinder), or actual leaks in the wheel cylinders (which you will see coming out of the vent holes on the hub and on your wheels).  Check every place that the brake lines connect and look for fluid leaks. All cylinder connections use a 17mm wrench, intermediate connections require a 10mm wrench, and the bleeder requires an 8mm.. Tighten all connections and make and try again.
Hoses and Lines:
Steel brake lines run from the master cylinder to a brass distribution block, and from there to a two steel lines to the wheel wells. Since I restored my car,  I found it easier to replace  these with new ones from the German club. The steel lines terminate where they meet rubber lines which flex as the front wheels turn. I’m told that on older cars these lines can bulge and but not necessarily leak, which will affect performance. Once again I simply replaced mine.
If your car ever sat for a long period of time your hubs might be rusty. My axles were very rusty and I had to use a larger puller to remove the hubs from the axles. This was an early warning sign that I might have to turn the inside of the hubs to get a good braking surface. You might be able to clean them up yourself, but a better idea is to bring them to a machine shop and have them turned. Here are some before and after pictures:
Brake Shoes:
Old brake shoes suffer from at least three potential problems; excessive wear, delamination, and absorption of leaking brake fluid.
I don’t know the minimum thickness but if you look at the brake shoes you should be able to tell if they are excessively worn. Both sides should have worn evenly. Delamination is a little different. Some brake shoes have the pads riveted to the backing plates with copper rivets. You should check to see if there are any issues with the mechanical connection of the pads to the backing. Absorption is a different matter. If your brakes have leaked into the pads they will not stop as well. Your options are to spray brake fluid onto the pads to try to clean them up. Alternatively you can just buy new pads from either te German or English clubs. 
Wheel cylinders:
Once again you are looking for signs of leaks. The typical leak spot is on the downward facing part of the wheel cylinder. If the inside seal is poor you’ll have fluid puddling and dripping onto the lower brake shoe.
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With hub removed , you can see metal and rubber brake lines, shoes, and wheel cylinders
Master Cylinder:
Aside from leaks there’s not much you can determine without some disassembly. 
In the next installment we’ll look at wheel cylinder repairs.
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