Electric Vehicle Brake Performance Tips

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Brake Maintenance & Performance Tips

For Electric Vehicles, it is imperative to have a properly functioning brake system; not just to maximize the brake effectiveness, but also to insure that our brakes are not eating away precious energy with unwanted rolling resistance. One very important advantage that electric cars have over internal combustion engines is they coast without using power, in effect providing "free" mileage. In addition, coasting allows the motor to cool down thereby making it easier to operate the motor within it's proper duty cycle. A properly adjusted brake system should allow the car to roll away from you if you lean (not push) against the back of the vehicle.

This article is primarily written for smaller E.V.'s like the Sebring CitiCar
but can easily be applied to all vehicles: Electric, Hybrid and Internal Combustion

Determining Brake Effectiveness - A quick way to check the condition of your brakes is to go for a five minute drive in a neighborhood where there are plenty of stop signs. After driving for five minutes, stop and park the car. Walk around to each wheel, reach inside the wheel and touch the rim. If the rim is warm, the brakes are working properly. If the brakes are too hot to touch, your brakes are too tight. If the brakes are cold to the touch, the brakes may NOT be working and should be further inspected, adjusted and/or rebuilt. If both rear brakes are hot, and front brakes are cool, make sure that the emergency brake cable is releasing. Do not confuse wheel bearing heat with brake generated heat

Use Caution THE BRAKES MIGHT BE HOT!

A visual inspection may be necessary. Safely raise the vehicle off the ground using approved jack stands. Remove the wheels and if needed the brake drums.

Inspect the braking system for dirt build-up. Brake dust can cake onto moving parts and cause binding.
Inspect for broken brake pads/shoes or missing springs
There should be no fluid around any part of the brake system. Evidence of fluid is be a sign of leaky seals
Check for even wearing of the brake pads, rotors or drums.

Don't forget to check the Master Cylinder for any evidence of leaking fluid. A Master Cylinder which is low on fluid may be evidence of a brake system leak, either at the master cylinder or at a wheel cylinder.

Correcting the Problems -

Take your time when repairing the brake components - Your Life May Depend On It !!!

Consider rebuilding only one wheel at a time. Should there be some question on how to reassemble the components, you can refer to the "untouched" side.

Do not reuse rubber seals. If they didn't leak before, they will soon. Quality rebuild kits will contain all the rubber seals you'll need for the job. Make sure you have the parts in hand before you start.

Brake systems must be clean... be sure to remove any built up dirt and oils. Lubricate moving parts with a dry lubricant or grease designed for the application.

Insure that the wheel bearings are properly installed and properly pre-loaded. Worn or improperly pre-loaded bearings may cause the brakes to drag intermittently.

Make sure that other components such as the emergency brake system are releasing entirely and not interfering with the proper operation of the hydraulic brake system.

Bleeding the brakes - There is plenty of good information on how to bleed hydraulic brake systems, Electric Vehicle Brakes are no different. However, there isn't as much room for error. Most E.V.'s do not have power assist, and the braking system can be undersized in comparison to an over powered internal combustion vehicle. The following tips may help fine tune the braking system.

After the air is out of the brake line, give about 8-10 more pumps on the brake pedal before closing the bleed valve. A good bleed job can use the better part of a quart or more of brake fluid. Make sure the reservoir stays full at all times.

Always use clean brake fluid from a sealed container. Brake fluid that has been in an open container (even if the lid is replaced on the container) can contain water, it is very hydroscopic.

When pumping brakes, pedal should be pressed slowly. Rapid pumping can cause the air in the lines to "foam" which can be very difficult to remove from the brake lines.

Never pump the pedal any further than it will go under normal operating conditions. Bleeding the brake system allows the piston in the master cylinder to travel further than it would under normal operation. The rust and debris that accumulates in this area can cut the seals causing the master cylinder to leak. Place a 2/4 or other suitable spacers under the brake pedal before you open the brake lines to prevent excess pedal travel.

Do not allow excess brake fluid to remain on the vehicle. It will dissolve most paint and collect moisture, which can cause the metal components to rust.

Cleanliness is critical. All components should be clean and travel smoothly. Remove any corrosion or built-up grease. Calipers Pins and other moving parts should only be lubricated with application specific grease.

When the brake pedal is pressed, the cylinders in the torque spider expand, but they have a very limited travel. This means that the shoes MUST be adjusted to within a hairs width of the rim to work properly. The best way to do that is to jack the car up, and spin the wheel that you wish to adjust. With a screwdriver, turn the adjustment gear clockwise (down) until the brake shoe just starts to grab the rim/drum. Next, take the screw driver and turn the adjustment gear counterclockwise (up) approximately 1/4 turn or until there is little or no drag on the drum. Let the car down and drive it around the block. If you cannot feel a drag, you probably have a good adjustment. If you can feel or hear the shoe dragging against the rim, return home, jack up the car, and turn the adjustment gear counterclockwise until the wheel turns freely. The end result is that the there should be no more space between the brake shoe and the rim/drum than the thickness of a piece of Post Card.

Before adjusting the brakes be sure to check that the brakes are operating correctly. Attempting to adjust brakes if any part of the system is binding, leaking or not functioning correctly is an exercise in futility.

Brake Fluid Options - Much controversy concerns the selection of brake fluids. So often, non-functional braking systems are disassembled only to find them gummed up with rust and corrosion. Invariably the brake fluid is blamed as the culprit, the age old scapegoat of the automotive brake system world! Before blaming the fluid, consider the following:

DOT5 brake fluid's "claim to fame" is that it does not absorb fluid because it is silicone based. Water will still accumulate in the brake system. Instead if mixing uniformly throughout the system, it tends to collect in the "low points" of the brake system making it hard to flush the water from the system. Because it pools in localized areas, corrosion can go undetected. DOT5 relies on the silicone (and minor amounts of corrosion inhibitors) to control corrosion.

DOT 3 & 4 can achieve as much as 3-4% water content, which is easily handled by corrosion inhibitors in the brake fluid. Unfortunately these corrosion inhibitors break down over time, so the brake fluid should be changed annually.

DOT 5 fluids ARE NOT COMPATIBLE with DOT3 & 4 fluids. Since almost all brake systems come from the factory with DOT3 fluids, and DOT 5 is also not compatible with most typical brake flushing materials such as mineral spirits and alcohol, the only recommended method to convert to DOT5 is to totally rebuild/replace the entire brake system.

DOT 5 fluid is not compatible with silicone based rubber components sometimes used in piston caliper boots.

The silicone in DOT 5 fluid bonds with any dirt, petroleum and and worn rubber components (even from normal wear and tear of brake system components) which creates a "gelatin like goop" which can lead to further plugging of the brake system.

Special Thanks to Cliff Ruffner for jump starting this article and providing valuable technical assistance.
Be sure to visit his site at www.aboatbuildingjournal.com