McLaren MP4-12C: DIY brake system overhaul

The McLaren MP4-12C is an amazing driver's vehicle. I've driven my 2012 all over California and loved every second. I've had it on track just a couple times, and it always impresses me. But I took it out for a few laps at Sonoma Raceway one day and I was getting very weird brake response. The brakes were not stopping with full power and were unsettling the car, dancing a bit left and right going into hard brake zones like Turn 7 and Turn 11. And if you've ever gone into Turn 11 at Sonoma at high speed, you know that the last thing you want is to feel unsure about the car's direction or stopping power. There's a pretty ominous wall in front of you as you approach at 120+ MPH.

I cut the day short at the track. Good thing, too. Taking off a wheel when I got home, I could see that the OEM brake rotors were more than a bit worn. More importantly, I could see that the pads had been wearing very unevenly... the top of the pad was thicker than the bottom, which meant the brake calipers were exerting uneven pressure. At least one of the caliper pistons was stuck or hindered.  It was time for a complete brake overhaul. I called the dealership: estimate was $18,000. Holy cow. New brake calipers, new rotors, new pads, full system flush. I decided I could do it myself for well under $4000. The brake calipers were the most expensive part, so I contacted the manufacturer of the OEM calipers (AP Racing), and they said they could rebuild the calipers to factory spec for $160 each. I found that Girodisc makes rotors for the 12C for about $700 per wheel. Plus pads for a reasonable price.  Yup, I could do it all myself for under $4K.

First thing to do was to get the car up on my Quickjack. This required the rail extenders because the jack points are spread fairly wide along the wheelbase. The extender rails for the quick jack also add height to the jack itself (because they are stacked on top of the base rail), so the jack was now too tall to slide under the car.  So, to get the car high enough to slide the jacks under it, I drove it up onto 4 small blocks of 2x4 wood placed forward of each tire. Up she went another 1.5 inches and that allowed the QuickJack to slide under and place the rubber blocks at the proper jack points. I bought all my components but the first thing I needed to get done was to send the calipers to AC Racing via their US partner Essex Parts).

The MP4-12C brakes are pretty easy to work on. First step is to make sure you have turned OFF the electronic parking brake so that when you work on the rears, they won't be in park mode (more on this later). The parking brake automatically engages when you turn off the car. You have to go through steps so that the brake does not come on when you turn off the car. This is key, or you will will not be able to remove the rear rotors (unless you do what I did, which is to hack into the parking brake with a battery and a couple wire leads later.... not easy). 

To remove the brake pads, you simply tap out the two retaining pins using a center punch. They are held in place by the spring clip, so it's easier if you take pressure off them by pushing inward on that flat metal retainer with the down arrow stamped in.

Once you remove the pins, you can use a caliper spreaders (or a large set of pliers and a soft cloth) to spread the pads and compressing the caliper pistons back into the rotor.

You can then gently work out the brake pad wear sensor which is held into its slot with a small pressure clip. Just work it back and forth to remove without breaking it. These can be re-used or can also be replaced, as I chose to do in this case.

With the rotors free of the pads, you an how use the proper Torx bit to remove the rotors.

Then it was time to remove the caliper itself, which is held on by two large bolts into the spindle. You have to disconnect the brake line, so have a catch can for fluid loss.

I removed the front calipers and prepared them to send to AP racing for rebuild. I was about to move to the rear but figured I'd put on the shiny new rotors from Girodisc on the front first. They are slightly larger in diameter (more surface area for heat dissipation) and, depending on your car and application, generally come with a spacer and longer single bolts to accommodate the larger diameter. Already looking better! 

Now it was time to remove the rear rotors and calipers. Ah, but here is where I discovered my parking brake error. The parking brake was fully engaged. I had no way of removing the calipers if the parking brake is engaged.  S&%T. The only way to disengage the parking brake is by first turning the car on (car must be running, not just be in accessory mode). But wait: I have disconnected the front brake lines and there is no pressure in the brake system. Damn. Which means the car will not let me start the engine (brake pedal myst be applied to hit the start button.  No car start, no brake disengage. No good. Hmmm, I called myself a few choice names, most of which I deserved.  Then I started to do some Google searching and I learned that you can zap the rear parking brake piston from a battery to engage and disengage. 

So I removed the battery from another car and hooked it up to a couple wires I had with alligator clips at each end. On the backside of the parking brake caliper I found the small wiring harness that plugs in there. I removed that and saw two leads. Depending on how you hook up your negative and positive leads, the piston in the caliper will engage tighter or it will loosen up. I tested it by hooking the clips to the caliper leads, then hitting a quick tap on the battery terminal.  I heard the electric parking brake make a noise and it presumably moved. The rotor didn't seem to be any looser, so I assumed I may be causing it to tighten. I switched the leads and did a couple test taps again. The rotor appeared to free up a bit so I surmised that I had the correct "direction". I tapped a couple more times lightly and noted my ability to now turn the rotor a bit. I tapped some more an the parking brake fully retracted.  Yay! Crisis averted. Although this little detour added a couple hours and lots of stress and swearing to my brake job. I started to wonder if $18K wasn't such a bad deal?

With the parking brake pad removed I could now remove the rotors, pads and rear calipers (no need to remove the smaller parking brake caliper because it wasn't being rebuilt). I repeated the same process from the front and soon had all four new rotors installed. 

Now it was just a waiting game while I mailed the calipers to AP Racing and waited for them to return. It took a bit, but eventually they came back, beautifully refurbished and ready to go. This alone saved me $9K in not having to buy new calipers from McLaren. AP painted them black again. I had considered a color change but thought I'd keep it stock. I sourced my own decals elsewhere to finalize the look.

 

Now it was just time to bleed the brakes. I put on my PowerBleeder, drained the old fluid out of the master cylinder with a turkey baster, filled the master back up with Motul 600 brake fluid, and started bleeding away.  Easy stuff if you have a good 11mm box/open/line wrench and a bleeder hose and catch-container.

When it was all done, it felt pretty good! Once I started the car, the brakes came nicely up to pressure after a few brake pumps and I managed not to go flying out the back of the garage with no brakes. Happy car, happy owner.  Ready for adventures again!