C8 Corvette Z06/Z07: Addressing ABS Concerns with Our Essex Competition Brake Kits

Over the past couple of years, we've heard from a couple C8 Z06 and Z07 owners who have experienced some unusual ABS behavior while running our AP Racing by Essex Competition Brake Kits. We've also seen some of the discussions surrounding these issues on the Corvette Forum, social media groups, etc. While these experiences have only affected a few individuals, we certainly understand why they would give some owners pause when considering a brake upgrade for their C8Z.

Rather than speculate about what might be happening, we decided to take a deeper dive. Our engineering team conducted a series of controlled tests at Carolina Motorsports Park, comparing the factory brake system with several configurations of our AP Racing Competition Brake Kits. What we discovered was particularly interesting, and it highlights just how closely integrated the mechanical and electronic systems have become on modern performance cars. More importantly, we identified the underlying issue and validated a surprisingly simple solution that allows owners to retain the significant performance benefits of our Competition Brake Kits.

Below is the complete technical bulletin from Jordan Bogue, Essex's Technical Director. It details the testing, findings, and our recommendations for C8 Z06/Z07 owners.

Text version:

The background

Modern automotive design has seen a marked increase in the depth of integration between traditionally mechanical systems and advanced electronic management.Brake systems are no exception to this trend.No platform has demonstrated this phenomenon quite like the 8^th generation of the Corvette.From the jump it was clear that General Motors was intent on making this newest iteration perform at the absolute maximum of its capability… and do it straight from the dealer.With that said, experience has shown us this philosophy can come with its fair share of headaches.. at least for those who pursue even higher performance.

For the brakes system specifically, this has meant battling with the vehicle control system about where race performance begins and the laws of physics end.Over time, particularly after the release of the Z07 package, word began to reach Essex of customers experiencing strange ABS intervention.Even a few instances of overall braking performance being impacted were also reported.This was quite puzzling.We knew our system was correct by the numbers with regard to torque output (disc size and piston area) and balance (front vs rear). This meant that the car should perform more responsively as a whole, and with dramatically increased thermal capacity. So where could an issue like this come from? Ultimately a decision was made. The only way to determine the validity of these claims, and validate a solution, would be to test it on track ourselves.

The Test

To isolate the origin of the issue, three different system configurations were tested (based on information our engineering staff learned ahead of time).The three rounds consisted of the following: 1. Baseline testing with the factory brake system (OE calipers, discs, pads, and lines) 2. The full Essex brake system 390mm front and 378mm rear (race calipers, race discs, Ferodo pads, and Spiegler lines)3. The full Essex brake system but with the OE rubber brake lines.All configurations were tested at Carolina Motorsports Park, with both an OE wheel/tire combo and a common aftermarket high performance wheel/tire combo.

The results

As it turned out, the root of the issue had to do with how much better the Essex competition system really is!

All joking aside, a common quality metric for racing brake systems has to do with compliance, often referred to in terms of system stiffness.The stiffer a system is, the less master cylinder travel (pedal travel) is required to achieve a hydraulic pressure in the system.Generally, this is a great thing as it makes the system feel more responsive and allows for quicker building, and release, of brake pressure.However, we learned this is not always the case.

In the case of the C8, each car has a vehicle control system integrated with the ABS calibration. This model has been tuned with the stiffness of the installed OE system (calipers, discs, pads, and lines).It is so narrowly tuned, that any major deviation from the stiffness of the factory system can cause ABS events to occur earlier in a stop and/or feel more ‘violent’.This is due to the system basing pressure release (and build) decisions around that full vehicle model as mentioned earlier.In plain English, take a scenario where the system wanted to release 200psi from the right front.With the OE system it likely releases a target volume and comes very close to 200psi of pressure drop.However, with a much stiffer system it might release the same volume of fluid but actually result in a ~300psi pressure drop.This same phenomenon would occur for pressure building as well.This presents itself to the driver as extremely rough ABS intervention along with overactivity.This is all due to the system’s reduced ability to hone in on a target slip ratio.

The solution

The answer to this issue was to add a known quantity of compliance back into the system, but without losing critical performance.The best way to do this?Install the OE brake lines onto the, otherwise complete, Essex Competition System.This solution retained all the critical benefits of running a competition brake kit (thermal capacity, weight reduction, durability, etc.) while putting the system back within the bounds of the ABS stiffness calibration.

The recommendation

All Essex C8 Corvette kits will continue to be supplied with Spiegler stainless-steel braided brake lines which still hold benefits over the OE style line (rock strike protection, firmer pedal feel, etc.). However, on any C8, particularly those with carbon-ceramic setups from factory, some customers may experience smoother, or less dramatic ABS intervention if the OE rubber brake lines are retained. In order to run the OE rubber brake lines with our Competition Brake Kit, the stock banjo bolts and crush washers must be replaced with those provided by Essex.

This solution has been proven by Essex Parts Services.