A torchin' bolt-on.

A torchin' bolt-on.

"These build journal entries are part of a Special Series on the development of the e9X M3 Custom AP Racing Big Brake Kits by HaimusRacing and written in collaboration with Antonio and his engineering team. 

In this entry, we finally complete the kit by installing the rear components. We touch on the usual rapid restorations while in there, pump to eternity and I give a preview to my initial impressions.

TL;DR: shifting bias to the rear is real." 
- Matt

Do it once, do it right. 

I wasn't at InnovAuto when we first fitted the front part of this big brake kit. Phil manage the installed in 2 hours - and as it with most things guys, it's easy. 

Having taken part in the installation of the rear kit, I felt it necessary to provide a detailed documentation of installing the brake kits, and recommended while-you're-in-there restorations of critical components. I will also compare the OEM rear components with the AP Racing custom components. 

As previously documented my unboxing impressions of the rear kit: this is a complete kit - nothing pertaining to your OEM braking system at the rear will be retained. 

This can be DIY'ed by most. It's relatively straight forward [...] unless you run into rusted bolts. If you do, please be self aware, take it to a shop and let them take on liability :) 

Removing the rear calipers and rotors is pretty easy: 2x small screws holding the rotor to the knuckle, 2x bolts / pins for the caliper to the bracket, 2x bigger bolts to the knuckle and the pad retainer spring. 

Wear goggles, at all times. These can jump out further than you think. 

Rapid Restoration. 

My rear end went through a partial restoration in late 2021: we recoated the rear subframe, sanded and painted the e-brake drums, painted the half shafts, diff and center exhaust bracket. 

We fell short of replacing the rear hub. My M3 hasn't seen Winter since, but still they needed help. 

We grinded the hub down to bare metal. 

Pulled out the aerosol rust prevention coating. 

Bam! It tac dries to the touch in a few minutes and dries out to a matte black finish. 

Proof is in the pudding! We have used this technique on the e-brake drums over 2 years ago, and they look as they were back then. 

Uh Oh - rust!

BMW M had the tendency back then to use non coated, standard steel bolts - and they had the brilliant idea to use such a bolt on the rear brake lines. 

The HaimusRacing kit comes with new braided lines with stainless steel hardware. The OEM lines need to come out. 

Removing them from the caliper is easy. We pinche them to avoid making a mess, and pumping brakes through the system for hours later on. 

Removing the lines from the subframe's bracket, however, is a whole different story. The bolt is on the brake line and cannot be replaced. If you thread this, it's done for. 

Now, why would we put cloth all over my recently painted subframe?

Remember what I said about this being a DIY? It stops being my recommendation here. 

Seriously, don't DIY this if you've never used a torch before. 

BAM! We made it. No bolts threaded, no body hair lost. and a subframe still intact. We probably added an hour or two to the install because of this. 

The little modifications. 

The Custom AP Racing BBK by HaimusRacing is considered a bolt-on modification, but it does require two small modifications to be compatible with the higher performing components. 

The brake line brackets. 

The WoodRidge brake lines have a different connector design that require a slight modification to the bracket. 

You need to slightly enlarge the bracket with a dremel. That's it!

The rotor shields.

The AP Racing rear caliper is 4 piston, and is dimensionally massive compared to the measly 1 piston floating rotor. As such, the rotor shield needs to be trimmed to fit the bracket. 

You don't want to remove the entire shield. It's required to safely run this kit on the street as it prevents debris lodging itself behind the rotor and caliper assembly. 

The grey'ish is a small dab of anti-seize. 

The bolt on starts here. 

From this point on, it's a quick road to finalizing the installation. The rotors get bolted using the 2x small allen bolts. We didn't replace them here as we had before, but I would highly recommend you do if you haven't.

The rotors can only be fitted one way and the hats are pre-drilled in the correct orientation to be fully compatible with the OEM e-brakes. 

Turner offers stainless steel bolts that won't ever rust. I previously spent an hour drilling out one of these in my garage. It was fun. 

Make sure the slotted rotors are on the right direction as it may other lead to premature wear due to poor thermal dissipation. 

We fitted the HaimusRacing brackets first using the OEM bolts to the knuckle. It was finally time to mount the beauty that is this RadiCal-4 caliper painted ala GTS. 

The calipers come with AP Racing's bolts. Unlike the OEM calipers, these don't have caps. 

The OEM calipers are bolted towards the outside of the car whereas the AP calipers are bolted to the bracket towards the front of the car. It makes for an easier installation and proper torque specs.

You can see how the brake line is bolted to the caliper as well. It comes with 2x copper crush washers. 

It was now time to fit the pads - and this is where these calipers shine. They were designed for rapid change change. The caliper stays on the bracket until it needs a rebuild. 

It's only a matter of 2x bolts, 2x pins and a clip. 

And voila, you got yourself a fully installed kit - or close. A pumping session is next. 

Pumpin' muscles & brakes. 

You think you're done? Nah. Bleeding brakes off a race-bred caliper is different than OEM calipers. 

Different how? These calipers hold more fluids and have 2x fluid channels across the caliper construction instead of 1x on the standard calipers. 

You're going to get a leg, and calves pump, big time. This means twice the pumping! Here's one of the two. 

Brake fluid notes. 

I usually use Motul's RB660F - but we were short on time and opted for what we had around the shop. KeenFlo is a DOT4 rated fluid and has lower boiling temperatures than Motul's fluids. 

Specs KeenFlo  Motul RB660F
Effective temperature range -40°C to 246°C (-40°F to 475°F) -
Minimum Dry Boiling Point:  246°C (475°F) 325°C (617°F)
Minimum Wet Boiling Point: 160°C (320°F) 204°C (399°F)


Not ideal, but it'll do as I don't plan on tracking the car this Fall. We popped the car, filled it out the edge, and it was time to start pump. 

Who did the pumpin'? The camera guy of course. Nike couldn't save me here. Pumping these brakes took 15 minutes total. They hold more fluid, and we have twice the channels to bleed. 

The DME doesn't like having its rear end off the ground with no wheels and tires. It threw a bunch of codes while we did the final bleeding procedure with the engine turned on. Worry not, these go away afterwards. 

And voila - we finally had a complete braking system fully fitted, and ready to get beat on for pad bedding and first impressions. 


Up next: I beat the hell out of it and get surprised, extremely surprised.

Forum bros will tell you rear big brake kits do little to performance and you can do without. 

Not when you shift bias to the rear: get ready to get anchored. 

Leave a comment

Please note, comments must be approved before they are published

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

The latest entries to the Stripper's build journal

I help you save money on everything you need for your E9x M3.

ConnexPlus is a premium membership for the most demanding BMW M owners.

A select group of members will save on everything they will ever need for their BMW M cars at the world's biggest BMW parts retailers.