Parking Brake

I purchased the option parking brake kit from Superlite. Although it provides all of the key components the builder still needs to fabricate a custom bracket for the brake lever and route the cables to the calipers on the rear wheels. While this isn’t complicated, it’s a pain in the ass. My biggest issue was trying to figure out where to locate the lever in the cramped cockpit. This is why many builders replace the lever with an E-Stopp electric brake kit. Essentially it’s a linear actuator with an Electronic Control Unit (ECU) that utilizes a button to toggle between no tension (brake off ) and 600 pounds of tension (brake on). The unit is used in many hot rods and SL-Cs. Most SL-C builders mount the unit in one of the side pods. The issue with this location is that you have to take the body off to service it.

I spent a lot of time thinking about where to place the E-Stopp and one of Stephen’s forum posts provided the answer. He mounted the unit in the recessed floor which affords easy access for maintenance. I was already planning on creating a closeout panel that wrapped around the chair to create a flat floor. I figured it would be a great place for luggage. I figured I could could fit a T-shirt, boxers, socks and toothbrush is a Ziploc bag LOL. Stephen also fabricated a channel to protect the cables… brilliant!

So that was the plan until I spoke with Allan and Bob. Allan has successfully used the E-Stopp in multiple cars, but he’s had two cars in which he couldn’t reliably get the parking brake to hold. He called the manufacturer to see if he could increase the 600-pound tension and they indicated that they’d have to completely redesign the unit. Bob also had similar issues and his car let loose while on a trailer. He spent a fair amount of time trying to get it to work reliably to no avail. While many people have had success with the E-Stopp, two very talented builders have had issues with it while the car was in the build stage.

Back to the drawing board. I then discovered motor-on-caliper parking brakes. Instead of using a cable to actuate the caliper these systems utilize an ECU to drive motors that are directly attached to the calipers. Apparently TRW has shipped over 60 million units and Brembo and other manufacturers have integrated the motor directly into the hydraulic caliper. This reduces unsprung weight by removing the need for a separate caliper and bracket. It’s my understanding that some systems implement a true emergency brake by using accelerometers to ensure that the car doesn’t spin when the brake is applied.

The TRW looked like an ideal solution. I tried to buy an aftermarket version or at least get documentation on an OEM version to no avail. So to the junk yard I went. It’s easy to pull the calipers and ECU, but I couldn’t figure out how to activate them. I tried using a CAN bus sniffer on a running car to figure which CAN bus messages where used to activate and deactivate the brake. My conclusion was that that the e-brake ECU are typically deeply integrated into the OEM’s system and that it wasn’t going to be as easy as finding two messages and broadcasting them. There’s likely a OEM implementation out there that might be that simple, but god knows how long it would take to find.

So after over a year of intermittent researching and tinkering I ordered an E-Stopp. On the day it arrived I decided to do one final search before opening the box and installing it following Stephen’s method…. AND I found this… HiSpec Motorsport Spot Electric Parking Brake (EPB) Really?

It’s a standalone solution that includes two calipers and an ECU! To prevent accidental engagement/disengagement you need to hold the button down for two seconds. The harness enables the addition of a backlit button or LED to indicate when the brake is engaged. My understanding is that it has adjustable tension and that it’s capable of holding a mid-size truck (will get specs from Hispec). At £640.00 (~$835.00) they’re a good value given that the Superlite option costs $999 and an E-Stopp costs $479.00. I asked them the weight of the caliper/pads/motor and I’m pretty sure they said 1.2kg (2.6 pounds). I weighed the Superlite brake caliper and it was 3.2 pounds. I had assumed the the Hispec unit would have lower total weight, but a higher unsprung weight due to the motor being mounted to the caliper. It seems too good to be true so I’ll validate the weight when it arrives.

So the benefits appear to be:

  • Significantly cleaner and easier installation

  • Lower total weight

  • Lower unsprung weight

  • Lower cost

  • Better holding power

The only downside that I can think of how to release the brake if the system fails or power is lost. They quote 28 days to manufacture the units after which point they are shipped from the UK. The next steps are:

  • Weigh the unit

  • 3D print a prototype bracket. This bracket will also double as a drilling jig. I will have tabs that enable it to be clamped to the upright and drill bushings to ensure straight holes.

  • Mount and test using the prototype brackets

  • Determine how to manually disengage the brakes

  • See if Fran is interested in selling CNC’d brackets