The RaceActive Chassis Control II suspension is the 720S's signature — and its signature maintenance bill. The system runs hydraulic fluid at high pressure through active dampers, and it's one of the few jobs on this car where cutting corners doesn't just cost money. It costs ride quality, it costs parts, and in a worst case it costs a very expensive cleanup. I did my flush at three years because the fluid was already visibly discolored — McLaren's interval is four years, but my car sees track days, and I don't trust "factory fluid color" as a standard. Here's the procedure the way I run it, and why each step exists.
Rule one: use the correct fluid. The RCC II system runs Pentosin CHF 11S. Not a generic power steering fluid. Not "something that's the right color." The seal and rubber compound in this system are formulated around CHF 11S's chemistry, and mixing in the wrong fluid degrades seals and packs with varnish that will make the next flush more expensive than this one. If you don't have CHF 11S, the flush is not happening.
Rule two: depressurize before you touch a line. This is the step the factory procedure exists to protect you from, and the one I would never skip. The system holds pressure in the accumulators even when the car is off. Disconnecting a fitting while pressure is in the system is how you get a jet of hot fluid across your hand and a cloud of fluid across your garage floor in the same half-second. The depressurization procedure in the manual walks through bringing the system to zero before any fitting is disturbed — read it first, then do it. It is not optional.
Follow the factory depressurization procedure in the manual exactly. The system must be brought to zero pressure before a single fitting is opened. If you have MDS, the procedure is straightforward — you command the system down and confirm the pressure is gone. If you don't have the tool, stop here and get to someone who does. This is the one step where "I'll just try it and see" is how people end up with an injury and a flooded garage.
With the system at zero pressure, open the drain points and let the old fluid out. Watch what comes out. Color is your first diagnostic — fresh CHF 11S is a clean, consistent color, and if it's dark, milky, or carrying particles, you've confirmed why the flush was needed. Milky can mean moisture, which is its own problem to chase. Note the volume you pull so you have a reference for how much the system actually held.
Now push fresh CHF 11S through the system until it comes out clean on the other end. This is the part where "a full flush" actually differs from "topping it up." You're displacing the old fluid that's sitting in the lines, the dampers, and the reservoir, and you only know you've done it when the fluid leaving the system matches the fluid you're putting in. Keep the flow steady, keep the reservoir fed, and don't let the system run dry or pull air in — air in a high-pressure hydraulic system is a different job to get out again.
Reconnect every fitting to the photo you took, torque to the values in the manual, and refill the reservoir to the specified level. Check the level after the system has settled, because the reading can shift once the fluid has stopped sloshing and the dampers have seated.
Bring the system back up and bleed out any air that got in during the flush. The factory procedure tells you how to cycle the suspension to work air out — you'll typically command the car up and down through its full travel range repeatedly until the movement is smooth and there's no sponginess or knock. Air in this system is not a "it'll work itself out" thing; it's ride quality you don't get back until it's properly bled.
Confirm the accumulator pre-charge is correct and that the system holds pressure with the car off — a slow pressure drop with the system shut down points at a leaking check valve or a weep somewhere you just reconnected. Then reset the service interval in the cluster and document the fluid, the volume, and the date. The next person who works on this system will thank you for the record.
McLaren's interval is four years. I run mine at three because my car sees track days, and track days mean the suspension is working at its limits more of the time, which means the fluid is doing more heat and shear work per year. The fluid being visibly discolored at three years told me the system had seen more than a gentle car would. If your 720S is a weekend cruiser that barely leaves the driveway, four years is probably fine. If it's on the track, treat the flush like a consumable, not an event.
Either way, the discipline is the same: correct fluid, system depressurized before any fitting moves, flushed until the out comes clean, bled until it's smooth, and a record of what you did. Do that and the RCC II is one of the most rewarding jobs on the car — you feel the difference in the ride the first time you drive it afterward.
This is the job that scares people most, so the two adjacent procedures I write up in the same style are the EPB service mode for caliper work and the M840T oil service. For the full depressurization and accumulator procedure text, torque values, and part references, open the service manual and go to the Chassis section.
Did your flush turn up something I didn't mention — a leaking fitting, a milky fluid, a pre-charge that wouldn't hold? Tell me. The goal is that the next person who reads this gets it right the first time.