Got Brakes?

(Written on 2/06/2022)

Test driving Penny before purchase had one little wrinkle: no brakes. The owner did make me aware that the brake pedal would have no effect. However, the parking brake did work, and allowed for a low-speed test drive around a flat yard. Once I got Penny to my house, I wanted to video the engine and transmission in operation. Going fast enough to use fourth gear requires brakes, so I decided to start with them as my first Penny project. The previous owner included new front brake calipers and rear brake cylinders with the car, but I opted not to use them yet. I am going to remove the body from the chassis, and completely redo everything including the brake lines. Connecting dirty, probably rusty, brake lines to the new calipers and cylinders would introduce dirt into them. Instead, I decided to pull the old calipers, rear cylinders, and master cylinder apart and clean them thoroughly to see if I could restore function.

With a curb weight of only 1,821 lbs, it's easy to put the Spitfire up on jack stands.

If you look closely at the first photo, you'll notice that the Spitfire has front discs and rear drums. The Spitfire doesn't have anti-lock brakes, and the whole system is dirt simple. Actually I'm old enough to remember when anti-lock brakes became standard equipment on cars. As a cocksure young driver, I disliked the idea of a mechanical device "thinking" for me. I was taught how to brake on ice and snow, and didn't particularly want the help, thanks. Don't get me wrong, modern anti-lock brakes are a huge safety improvement; I just have a very strong independent streak in me.

 

So if you already know how a simple brake system works, or you don't care to know, skip past this next part.

This excellent diagram is courtesy of www.buildyourownracecar.com. You can visit their site for additional details. The diagram shows how disk and drum brakes work. It's the same basic principle for each. Depressing the brake pedal pushes the piston in the master cylinder. This forces fluid out of that cylinder and into cylinders at the wheels. In the case of disc brakes, the cylinder is a caliper. When fluid is forced into the caliper, moving its piston(s), a set of brake pads are squeezed against a disk stopping its rotation. The disc is part of the wheel assembly, so stopping the disc, stops the wheel. Drum brakes have a brake cylinder. Forcing fluid into a brake cylinder forces the piston(s) outwards. The piston(s) presses the brake shoes against the inside of a drum, stopping its rotation. The drum is part of the wheel assembly. The major oversimplification in the diagrams above is the master cylinder. In reality a typical master cylinder contains two pistons. The output from one piston is piped to the front brakes, and the output from the second piston is piped to the rear brakes.

 This photo shows the front disc assembly with caliper.

This photo shows the rear brake drum assembly with the drum removed.

Hydraulic systems require an in-compressible fluid to transfer the force on the pedal to the pads and shoes at the wheels. Brake fluid is not only in-compressible, it is also designed to withstand high temperature, and not degrade rubber seals. I'll skip a discourse on the various types of brake fluids (DOT 2 - DOT 5), and the property trade offs of each. For years, the most common type of fluid used in the United States  is DOT 3. DOT 3 has the unfortunate and undesirable property of being hydrophilic. It has an affinity for water, and absorbs moisture over time. What this means to a car sitting for a quarter century is that the brake system corrodes internally. Obviously Doc and Marty did not use DOT 3 fluid in the DeLorean.

Here is Penny's disassembled disc brake caliper and piston. You can see the build up of sludge. This may just be from use over time. Once the gunk was cleaned off, both the caliper's cylinder and piston showed corrosion and pitting from water in the system.

Note that the caliper has been split apart. This is not recommended, and I would not do this to a caliper I intend to use long-term. Splitting the caliper could result in leaks. I re-torqued the halves together, and have not had any issues, but these will be replaced before the project is completed.

 

The  rear brake cylinder shown here clearly has mucho corrosion!

After freeing the piston, and cleaning everything, corrosion and pitting were clearly visible on the piston and cylinder. Left and right calipers and brake cylinders were pretty equally corroded.

 

As can be seen here, the master cylinder was also badly pitted due to corrosion.

 

Here is the master cylinder all cleaned up and ready for re-installation. Yes, those are foam earplugs being used to stop up the brake line holes.

I thoroughly cleaned and reassembled all the brake components without replacing any parts. They were then re-installed in Penny, new brake fluid added, and the brake system bled to remove any trapped air. So, how did my effort turn out? Penny now has brakes that function at a level sufficient for testing the engine and transmission, but not acceptable for daily driving. The brakes absolutely stop the car, and you can lock them up if desired. If you press on the brake pedal for an extended period, it will slowly sink towards the floor. I believe what is happening is that the brake fluid is seeping past the pistons in the master cylinder due to the pitting. Achieving this level of operation cost me nothing, and is really all I was looking for at this point.

Here is the video I was able to make after the brake job, showing Penny being shifted smoothly through all four gears.

If you work on cars, you probably noticed how small the rear brake components are. This got me thinking about their effectiveness. I prefer disc brakes for ease of maintenance, and discs have other advantages over drum brakes. I did a bit of research on possibly changing the rear drums to discs. What I found was that the Spitfire brakes work very well for a car of this weight. When something works really well, don't change it.

I hope you enjoyed this post as much as I enjoyed this brake project. Cheers, Gene