Designing, Manufacturing and Assembling a Custom GT40 Braking System
As the vehicle was broken down completely for shipping basic suspension assembly was completed first.
I did not purchase the standard RCR Wilwood brakes as they may not meet the ADR’s (Australian Design Rules) and while they fit in 15” diameter rims they look a little small to me inside the 17” rims. Looks are not everything, but I also wanted the challenge of designing a few alloy caliper brackets and rotor hats. The performance of the standard Wilwood RCR brakes are more than adequate, however this setup will be even better and with a larger disc diameter the pedal effort will be reduced.
I decided to use AP Racing calipers and DBA (local manufacturer) slotted rotors. The sizes I decided on (based on some basic brake balancing calculations) are below:
Front – AP Racing CP5555 6 pot calipers and 343mm (13.5”) x 32mm thick rotors Rear – AP Racing CP5200 4 pot calipers and 330mm (13”) x 28mm thick rotors
The rear rotors are quite large as the rear does a good deal of braking due to the weight in the rear of the car.
I also decided to use the Precision Brake Co. handbrake calipers on the rear. While I was designing the alloy brake components I had the logo changed on the face of the handbrake caliper. I modeled up the entire caliper (image below) with the AP Racing logo and had the original logo machined off and the AP Racing one machined in. The logo was then filled with high temperature gloss yellow paint. It’s a flat out lie but it looks better to me as it matches the main brake calipers!
I designed all the brackets myself on CAD by measuring the RCR parts, wheels etc. very carefully to ensure a perfect fit. I then had the rotor hats and caliper mounts CNC machined up directly from the CAD data here in Australia. For the front brake system no modifications to the RCR uprights were required to mount the upgraded brakes. However the rear brakes required some minor changes to the RCR uprights.
The front brakes were designed in the same way as the rear. however clearances between the caliper and rim were much closer as they are larger.
The front caliper clearance to the rim is as little as 2mm in some areas.
The rotor hats were designed without any holes to aid in cooling. The reason will be clear in a future post on brake cooling ducts.
During assembly I was a bit nervous, it all looked good on CAD but did I make a stuff up? Very happy to say all parts fit perfectly. On the rear I simply milled off the existing Wilwood caliper mount on the RCR upright and tapped some holes and bolted my custom brackets on. I’m also happy I found some great NC machinists to make the alloy parts and they are first quality. They will be used again for more custom machining work for my build.
As always these designs worked great for my car but should not be used by others without first having them checked by a qualified and certified engineer.