The Drum

Taming a Hellcat with Motul RBF 660

15.02.2019

Automotive journalist, Bradley Iger, on brake fade in his Challenger Hellcat and how Motul RBF 660 improves braking performance.

As an automotive journalist, I have the good fortune of being able to spend my days behind the wheel of many of the world’s most capable performance cars, both on the street and at the racetrack. When it came time to find something for myself a few years ago, I managed to narrow the list down to a few worthy candidates that fit my budget, offered the level of performance I wanted, and connected with me on an emotional level.

It was a tough decision, though – some cars are fantastic on a road course but terrible to drive day to day, or vice-versa. It wasn’t until I handed back the keys to a long term tester – a 2015 Dodge Challenger SRT Hellcat with a six-speed manual transmission – that I realized that this was a vehicle I needed in my life all the time.

The car can put a smile on your face just by looking at it – it’s the physical manifestation of the doodles I used to draw in margins of my notebook back in junior high. And once you get past the absurd amount of grunt on tap, you discover that it’s also a great grand touring machine that can legitimately hold its own on a racetrack. It checked all the boxes for me. I ordered my car in December of 2016 and took delivery of it a little less than four months later.

Since then the car has seen a few track days at courses here in Southern California and has spent a significant amount of time being caned on the twisting stretches of tarmac in and around the Angeles National Forest. The base of Angeles Crest is just a ten-minute drive from my home, making it the go-to whenever I want to shake some cobwebs loose.

Last summer I had a chance to run a few hot laps in the car around Thermal Club’s South Palm Circuit, a 1.8-mile, ten turn course that includes the longest straight at the facility. That straight leads to a relatively low-speed sweeper, and combined with two other lengthy straights that lead into tight hairpins, the course can give just about any brake system a serious workout.

To reign in the Challenger’s sizable girth as well as its ability to hit some pretty serious speeds in short order, SRT outfitted the Hellcat with the largest Brembo brake system they’d ever equipped to a production car at the time. It’s a package that works really well right out of the box… for about four or five hot laps around the South Palm course in the desert heat. While I wasn’t losing braking capability outright, after a half-dozen unrestrained laps the pedal was starting to creep closer and closer to the floorboard. I'd begin to scrub off all the speed at the end of the main straight to set up for a loss of braking into the sweeper. It quickly convinced me to cool down the car and head for the pits.

“When you’re talking about performance driving, the heat generated by the pads and the rotors can be enormous,” Joey Cabrera, Motul USA’s Technical Product Manager, told me. “By putting that type of load on the brakes repeatedly, it can get to the point where – if you don’t have the proper fluid for the way you’re using the car – the fluid will start to boil. After a while of allowing the fluid to boil and recover over and over, the formulation will start to break down and it just won’t be as effective anymore.”

And indeed, the factory fluid was never quite the same again – the pedal feel wasn’t as firm and the response at the top of the pedal stroke had dulled significantly. That’s when I realized the factory stuff just wasn’t enough for how I use the car.

“When the fluid is deteriorating, you’ll feel it in the brake pedal,” Cabrera explained. “The pedal will stop feeling ‘tight.’ When the brake fluid takes a while to return to a solution again as the heat dissipates, that means the fluid itself is breaking down. You’ll also notice that the fluid will look very dark and dirty when this starts to happen.”

After that stint at Thermal, I began to notice the brake fluid starting to boil even during extended jaunts through the Angeles Forest. It was clearly time to step up to a product that could withstand the abuse, so I ditched the worn-out factory stuff and put in some RBF 660.

“Having the proper equipment is essential for the brake system to work properly, and that includes the fluid,” Cabrera added. “RBF 660 is a DOT 4 fluid with a dry boiling point of 617°F and wet boiling point of 400°F, and it is designed to handle the high temperatures that can be generated by performance brakes. Very few production vehicles – even track-oriented models – come with brake fluid that can operate near this level. OEMs typically test the car to a level of what they expect from a typical consumer, and their choice of fluid often just comes down to cost.”

Outfitted with the right brake fluid for the kind of driving I do, the Challenger’s brake system is functioning even better than it did straight from the factory.

Now, if I could just find a performance tire that this car won’t turn into smoke and rubber chunks…