Secondary handbrake systems have many advantages and only a few minor disadvantages to in-line hydraulic handbrakes. The main disadvantage of full secondary systems is added unsprung weight. With lightweight parts like wilwood calipers, this is mitigated fairly well.
In contrast, in-line hydraulic handbrakes tap into the existing braking system. This adds complexity and risk to the factory brakes by adding more points of possible failure. There is a chance of uneven brake pressures front to rear if the regular brakes and the in-line hydraulic brakes are used simultaneously.
No matter the debate, a full secondary system is preferable to in-line. This is a generic tutorial for the E30 but only minor changes are needed for any vehicle.
Wilwood 120-9689 dual pistol calipers (buy two)
Wilwood GTO brake line kit wil-220-8756 (optional)
Wilwood grabby pads (only need to buy one)
Sikky handbrake with 5/8″ Master cylinder
2 psi residual pressure valve
A way to mount the calipers
Spare factory soft lines
Various metric hard lines, fittings, and one T fitting
To start, a handle and master cylinder should be chosen. ASD and Sikky both make basic handles that come with housings and your choice of master cylinder. Master cylinder sizing is of the utmost importance. The usual choice is between a 3/4″ or 5/8″ bore. The larger bore (3/4″) pushes more fluid but will take more effort. The positive side is that it will require less distance on depression to lock the wheels. The 5/8″ will be physically easier to actuate but may require a larger pull of the handle to lock the wheels. There is lots of math that goes into cylinder sizing but ASD has a nice Master cylinder sizing chart. These rely on the type of caliper being used in order to size the master properly.
The next part is really personal preference. The guys at Sikky sent me a banjo bolt for the wilwood master with a -3 AN soft stainless steel line. This saved me from having to manually bend hard lines, makes maintenance 100x easier, and made the install look much cleaner. With it, they gave me a little adapter that works to my hard lines. I purposefully did my entire install with metric hard lines that can be found at any auto parts store. The wilwood caliper came with a double flare fitting but everything in my install is a bubble flare.
Soon after my master there is a 2 psi residual pressure valve. This is standard in most disc braking systems. This keeps just enough pressure in the line that pumping the lever isn’t necessary to use the brakes but not enough to drag the brakes.
Once the line exits the body of the vehicle, a T fitting is used to split the output to each wheel. Since E30 trailing arms have a significant amount of movement, soft lines are used. For this I used upgraded factory stainless steel hard lines that I had spare. This way, the hard lines aren’t fatigued when the vehicle goes over bumps. This soft line leads into a short hard line and back into an adapter for the final -3 AN line from the GTO stainless steel brake line package from wilwood. This was used because it came with a 90 degree NPT fitting for the wilwood calipers and was adapted for the metric hard lines.
Finally, the choice of calipers was the same kind from the Massive Lee E30 handbrake kit. For different cars, different rotor diameters and thicknesses should be taken into account. The wilwood pads chosen were due to biting hard while cold as drifting shouldn’t ever overheat the pads. The Massive Lee caliper mounting kit removes the factory drum handbrake so I opted to have custom brackets welded to the bottom of the factory trailing arms. The bottom of the trailing arms is the only place that has a good flat spot for mounting. The down side is that bleeding requires unbolting the calipers and moving them to prevent air pockets.