As frustrating as it's been at times, progress has continued behind the scenes. Some problems have taken a lot longer to solve than expected, but that's all part of building a one-off car like this. There always seems to be another challenge waiting around the corner.
The good news is that there has actually been a lot happening, so it's time to catch everyone up on where the project is and what I've been working on.
As mentioned in my previous update, the ABS remained one of the biggest challenges. I eventually removed the original BMW ABS system because I simply couldn't get it to perform reliably under race conditions. In its place I fitted a Bosch MK60 unit. It's a much simpler system, easier to modify, and requires far fewer inputs to operate without shutting itself down.
Unfortunately, that didn't solve the braking problem. In fact, it made it worse. After fitting the MK60, the ABS became incredibly sensitive, activating far earlier than it should.
This led me down the path of researching whether I should simply remove the ABS altogether. After a lot of reading and advice from people with far more race experience than myself, it became clear that this wasn't really an option with my current brake setup. The combination of very large AP Racing front brakes, standard BMW 645i rear brakes, and a vacuum brake booster meant the front-to-rear brake balance simply wasn't correct. To make matters worse, the brake booster removes much of the mechanical feedback through the pedal, making it difficult to judge exactly what the tyres are doing under heavy braking.
The solution was to convert the car to a dual master cylinder pedal box with an adjustable brake bias system. I removed the brake booster completely and installed a universal pedal box from International Racing Supplies.
Being a universal unit, it wasn't exactly a bolt-in installation. Considerable modification was required to fit it correctly, especially to mount the brake fluid reservoirs as level as possible and package everything neatly inside the car.
Removing the brake booster also meant I had to change the pedal ratio. Without a booster, the original pedal ratio would have required an enormous amount of pedal effort to stop the car. Increasing the pedal ratio naturally increases pedal travel, and initially it felt completely wrong compared to a conventional boosted braking system.
An added advantage is that the brake bias can now be adjusted from inside the car while on track, allowing me to fine-tune the front-to-rear balance as conditions change.
Setting up the system sounds simple... at least in theory.
With all four wheels off the ground, one person slowly applies the brake pedal while another turns each wheel by hand. The goal is for the front wheels to lock first, with the rear wheels only just beginning to bind.
Simple enough... or so I thought.
Once I got the car onto the circuit, everything changed. Weight transfer under hard braking, tyre grip, suspension movement, and overall vehicle dynamics meant the static setup was no longer correct. Initially the rear wheels locked far too easily. After gradually dialing more brake bias to the front, I could clearly feel the balance moving forward until I reached the point where the front tyres locked first. After a few laps, though, I realized just how much feel and modulation I had gained. The control through the brake pedal is honestly incredible.
That was the moment everything made sense.
If you're running a race car without ABS, an adjustable brake bias system isn't really a luxury—it's essential. Every track, tyre, fuel load and setup change affects the optimum brake balance.
For now, however, I still intend to run the MK60 ABS system. When it's working correctly, ABS remains the safer and ultimately faster option. The challenge now is getting it to work properly.
I'll cover that saga, along with a few other ABS related gremlins and some exciting new modifications, in the next update.
