Building a Brake Kit
Hi guys, Mike from Prosport Auto here. I was contacted by a customer who was building a racing car for the New Zealand endurance series (NIERDC). I had to come up with a kit that would handle the braking requirements as well as keep running costs down.
The 3-hour endurance races are quite hard on brakes, especially with a heavily modified car. Hampton Downs and Manfield tracks will test any brake kit to the limit, regardless of chassis. Not only did we need a kit that has good thermal mass and cooling capacity, the car needs to stop well repeatedly.
Here are the steps that we go through when making recommendations for braking kits:
Consultation: I chatted with the customer about what was required. The setup is 4WD and moderate/high HP (600hp). Relatively heavy at around 1400kg also. For 3-hour endurance racing, we'll need something with really good cooling and medium/high thermal mass. On my recommendation they chose to use the WedsSport TC105N wheel. The TC105N has a tight barrel diameter, so around 360mm was the biggest disc we could use while maintaining decent caliper clearance. These wheels were 4kg lighter each (16kg per set) over the wheels the customer was looking to use. Big gains here.
We chose the RacingMONO6 caliper as it allows the use of a 25mm thickness brake pad. It's super strong and rigid, perfect for endurance racing. We can use either a 54mm or 62mm annulus pad (RD, swept face height), so this opened up our disc options. A larger annulus brake pad doesn't affect the stopping power, but increases life as there is more pad volume.
ENDLESS RacingMONO6 caliper. Forged monoblock construction, strong and rigid. 25mm thickness brake pads and can take up to a 36mm thickness disc.
For the brake disc, we chose an ENDLESS 350x33mm rotor with a 19mm airgap and 72 curved vane design. With a 64mm annulus, this gives us massive cooling surface area. The weight comes in at 8.0kg each. Heat treated and slotted, this would handle this application with ease.
Design: It was my job next to design a caliper bracket and brake bell/hat to suit the caliper's and disc's we're going to use. Fortunately, I was able to use a spare hub and an old brake caliper bracket to make reference measurements. Getting the offsets spot on is really important to make sure we can use the maximum thickness pad. With these ENDLESS RacingMONO6 calipers and a 33mm thickness disc, we can use a 26.5mm thickness pad while still having around 1mm clearance for heat expansion and ease of fitment.
Prosport Auto designed caliper brackets for the ENDLESS RacingMONO6 calipers.
It's important to not have the edge of the pads hanging over the edge of the disc when they are cold. Pads hanging over the edge of the disc will increase the chance of cracking discs as the outer edge runs really hot. A disc will grow up to around 3mm in diameter (1.5mm in radius), so there needs to be sufficient clearance to the caliper body also.
For the brake bells (also known as "hats"), there are a few dimensions which are critical. Firstly the bobbin slot dimensions need to be perfect. If they are too tight, the bobbins wont fit. If they are too big, the bobbins are sloppy and they will rattle and wear quickly. The bobbins are 11.93mm wide and I aimed for a 12.00mm slot after hard anodising (30 micron growth per surface). This allows the bobbin to grow with the disc heat, as the bobbin will be hotter than the bells.
Secondly, the hub mounting face and the disc mounting face need to be perfectly parallel. This eliminates any runout (wobble) concerns which doesn't really affect performance, but it really pisses the drivers off! Having a brake pedal that vibrates on application doesn't help with confidence.
Prosport Auto designed brake bells (hats). 5x114.3 PCD and 10x disc mounting PCD.
Manufacture: I got in touch with Dan Melling from KiwiCNC to help with the manufacture of our pieces. Dan has been producing CNC parts for Aircraft engines for a while now. Dan has an extreme eye for detail and was able to turn around our parts quickly.
Caliper brackets after their first operation in the CNC mill. These were made from steel 1045 rod.
Operation two on the caliper brackets finished. Prosport Auto branding and a part number engraved.
The caliper brackets all finished and ready for paint.
The bells are made from 6061-T6 aluminium rod. The caliper brackets we used a 1045 mild steel.
Brake bells all finished and ready for checking. Thicknesses are checked to make sure axial float is correct. Slots are checked to make sure the tolerances will be right once back from hard anodise.
Assembly: Once I received the parts back from Dan, I need to double check all the measurements and tolerances. I dummy fitted the discs to the bells, then attached the caliper and bracket to the hub. The end result was exactly as expected - perfect! It's nice to dummy fit these items up, it's always a relief when the "drawing department" (Me!) hasn't stuffed anything up.
Fresh off the CNC mill, the brake bells are test fitted onto the ENDLESS 350x33mm disc. Tolerances and dimensions are double checked.
Test fitting with a hub off the vehicle, it fits! Always good to double check everything before sending the bells off to anodising.
After test fitting, the bells go off to Advanced Anodising in Tokoroa for hard anodising. Marcel is the only company I know of that can turn around products in 2 days as an express service. The hard anodising is critical to get maximum life out of the bells. The bobbins are tough on the aluminium material, so every little bit of durability helps. When the disc gets hot, it will grow and the bobbins will slide in the slots in the brake bell. All while the brakes are applied and there is stopping force being generated, the slots get a hard life.
The final pieces of the puzzle. Bobbin kit with our hard anodised bells. The bobbin slots are re-checked after anodising to make sure they are where they need to be.
Fitment: Once everything is finished, I've got the fun job of delivering these items to an excited customer. I got to work test fitting the kit onto the car to ensure there were no issues with fitment. I run over the requirements for torque specs on the bolts and the orientation the kit is fitted in.
Our Prosport Auto brake kit all fitted without issues. It's always a nice feeling. The brake pad hanging out of the bottom of the caliper is not an issue, the brake pad will wear flat.
Plenty of clearance between the caliper and the WedsSport TC105N spokes. Notice the 26.5mm thickness brake pads with 62mm annulus (swept height).
Finished product - almost ready to roll. Only brake lines left to fit and everything to be torqued to spec.
The results are awesome, an excellent looking and performing kit. There is good clearance with the wheels, both from the spokes and the barrel.
We'll update you once the car has run and we've got customer feedback from the kit.
If you're wanting a brake kit for your setup - get in touch and we'll have a chat about your requirement are. I'll put my thinking cap on and come up with a solution that will get the job done.
Mike Cullingford, mike@prosportauto.co.nz, +64211747427, 09 2383560.