Custom AP Racing Brakes on a Classic Mini
Lets talk about adding a set of custom AP Racing Master Cylinders configured in a non-standard way, to fit better with my side mount turbo in the Classic Mini.
Heat Management
Many of you already know that I have a big honking turbo on my Classic Mini. This turbocharger sits on the left side of the engine, directly adjacent to my brake and clutch master cylinders. Some of you also probably are aware that turbos get really freaking hot.
This heat is only compounded and intensified as you put more load on the engine, and especially during the summer months, it can have big impacts on things located near the turbo.
In this case, my brake and clutch cylinders.
During original installation, I already partnered with HEL Performance to add heat-sleeved hydraulic lines, capable of handling 1200C/2200F, yes 1200C. Thinking this would be enough, I moved on to the rest of the build.
However, after getting into practical usage, I found that the original tin master cylinders ended up effectively acting as two little ovens for my brake fluid. Expanding the fluid to the point of overflowing (though I don’t think it was ever boiling), as well as creating brake fade, and issues engaging the clutch.
Solving the heat issue
After discovering this, I obviously needed to find a solution. Looking at alternatives, I came across the KAD Master Cylinder Kit, which uses two AP Racing masters and their own custom reservoir mount.
The kit looked awesome; however, the price tag did not. So I set out to find all the parts used in the kit, in hopes of building my own, and I am happy to say, I was able to do this.
Parts List for V1:
7/8in Cylinder Used for Brakes
Bore Size: .875 | 7/8 Inch
Pushrod Length: 115mm
Pushrod Thread: M8 x 1.25
AP SKU: CP2623
DT SKU: A/PCP2623-94PRM115
3/4in Cylinder Used for Clutch
Bore Size: .750 | 3/4 Inch
Pushrod Length: 115mm
Pushrod Thread: M8 x 1.25
AP SKU: CP2623
DT SKU: A/PCP2623-92PRM115
Reservoirs
Size: Short
Thread: 716 x 20 UNF
AP SKU: CP4709 Type
SKU: A/PCP4709-13
Link: https://geni.us/APRes
Heat Sleeve - https://geni.us/heatsleevecmdiy
Pedal Connectors - https://amzn.to/3KeIsjs
Master Cylinder 6mm Anodized Spacers - https://geni.us/APRacingSpacerMini
IMPORTANT: See Version 2 list further in the article for the extra items I had to order in order to solve some practical issues.
Using the parts above, plus custom-length lines, I set out to create a remote mount for the master cylinder reservoirs. These were mounted on the bulkhead, just to move the main fluid holders away from the downpipe.
This took a ton of prototyping and testing, but ultimately I did settle on a design that I felt would hold the cylinders in place, and decided to test it with “chemical resistant” filament ASA-CF (foreshadowing here).
After getting that mocked up, and ready to measure for custom lines, it was time to move onto cutting down the threaded rods on the bottom of the AP Master Cylinders.
These were way too long for the Mini and did end up requiring some pretty substantial cutting to get them to match the original length of the OEM Master Cylinders. Some things to note here when/if you are doing this on your own setup.
The overall length of the rods needs to include your new mounting Clevis Fork.
Thread on a nut before you cut, so when you remove it, it chases the threads on the rod.
IMPORTANT: Even with the cuts and measuring, you will need to run these AP Racing master cylinders with a 6mm thick spacer. You can order two from my store - https://geni.us/APRacingSpacerMini
I didn’t capture the process of cutting these, but I feel like it’s pretty straightforward. They just have to match (factoring in the 6mm spacer).
After everything was installed, it looked really pretty good (considering how many lines it needed), but it was a tad bit crowded. At this stage, I was good with it being Version 1, and I took the mini to the Classic Minis United trip and put about 800 miles on the car.
Not so Chemical Resistant After All…
After getting back, I discovered the ASA-CF I used was not, in fact, resistant to DOT3/4 brake fluid, and after the heat + fluid exposure became incredibly brittle. This caused the reservoirs to just flop about in the engine compartment.
Obviously not ideal…
With this, I had to come up with another revision that solved this issue with something more resilient.
This is where I looked at the KAD kit, thinking “How can I replicate this, while keeping the reservoirs far away from the downpipe?”. What I came up with used a few extra parts. Specifically, it also required designing a new mounting bracket for the backwards orientation.
Version 2 Additional Parts
2 x 4AN | 90 Degree Female/Female Adapters - https://amzn.to/4mrhe6u
2 x 4AN | Straight Male/Male Adapters - https://geni.us/4anMMAdapters
3in 5/16”-24 Internally Threaded Connecting Rod - https://www.mcmaster.com/catalog/131/1502/7417N54
Custom Designed Mounting Bracket - https://geni.us/APRacingResBracket
Seen here is the prototype for the new mounting bracket I designed, before I got the anodized aluminum laser cut version.
And then here you can see the orientation I chose to go with on the AN4 adapters. Fair warning, when installing all of these bits, it is extremely hard to get everything tightened and takes a considerable amount of fiddling. They all go in, in a specific order, to get them properly torqued down.
The Final Product
After road testing, considerable amounts of time printing, and prototyping, I have essentially designed the setup that KAD made, but set up to be oriented backwards for my specific needs. The braking performance and clutch performance are now exceptional, and I have no issues with heat whatsoever. The last thing I was going to consider was designing a small heat shield between the master’s and the downpipe; however, I have not had a single issue with heat since installing version 2.
Final Complete Parts List
7/8 Cylinder Used for Brakes
Bore Size: .875 | 7/8 Inch
Pushrod Length: 115mm
Pushrod Thread: M8 x 1.25
AP SKU: CP2623
DT SKU: A/PCP2623-94PRM115
3/4 Cylinder Used for Clutch
Bore Size: .750 | 3/4 Inch
Pushrod Length: 115mm
Pushrod Thread: M8 x 1.25
AP SKU: CP2623
DT SKU: A/PCP2623-92PRM115
Reservoirs
Size: Short
Thread: 716 x 20 UNF
AP SKU: CP4709 Type
SKU: A/PCP4709-13
Link: https://geni.us/APRes
Pedal Connectors - https://amzn.to/3KeIsjs
Master Cylinder 6mm Anodized Spacers - https://geni.us/APRacingSpacerMini
2 x 4AN | 90 Degree Female/Female Adapters - https://amzn.to/4mrhe6u
2 x 4AN | Straight Male/Male Adapters - https://geni.us/4anMMAdapters
3in 5/16”-24 Internally Threaded Connecting Rod - https://www.mcmaster.com/catalog/131/1502/7417N54
Custom Designed Mounting Bracket - https://geni.us/APRacingResBracket