As expected, after replacing the brake fluid with fresh DOT4, overhauling the master cylinder, and replacing the ageing brake lines with stainless steel hydraulic hose, the feel on the front brake has improved substantially. It is quite sufficient for road use. There's enough progression to brake controllably, and enough feedback to sense imminent lock-up of the front wheel."I'm going to change the brake lines on the PCX this weekend. It's tempting to remove the Combi Brake connection and plumb a second line from the handlebar master cylinder to the "Combi piston" in the front brake caliper. But the goal isn't to increase the braking force, it is to increase the "feel" through the brake lever."
For those who haven't done it before, fitting braided lines is super-easy. You need a sharp cable cutter, circlip pliers and a small steel file (see note below), some stainless brake fittings for each end, and some brass washers. A torque wrench is recommended with 13mm or 14mm sockets for the banjo bolts (they can be either), and you will need an 8mm spanner for the bleed valve on the caliper. A length of clear plastic pipe ID 8mm (or a few zipties to attach larger OD tube), and a throw-away plastic bottle will complete your kit. Arm yourself with the PCX150 service manual and watch a couple of YouTube instructional videos. The whole job can be done in under two hours (first time).
How it worked out in practice
The front brake line was cut to 41". I thought 40" would be right. As it turned out, the line had to be cut back to approx 37.5" to fit correctly. Not a problem with a sharp cable cutter. Note, to get the new brake hose to fit your shiny new stainless end fittings, carefully cut 3mm of plastic away from the end of the brake line. Then fit the stainless fitting. It will go on much more easily.
In my case, having drained the original brake lines and attached the new ones, the master cylinder refused to pressurize the new brake line. It was time to get a Honda master cylinder repair kit.
Master Cylinder Repair Kit for 2012 PCX150
Master Cylinder Repair Kit for 2013 & onwards PCX150
The part number for 2013+ PCX150's is 45530-KVY-911. Don't use this part unless your bike is 2013 and later (a no-seat-hump version). This is the part I ordered and waited two days to arrive. And which didn't fit.
Why would the master cylinders be different? Once suspects that after customer feedback Honda fitted a slightly smaller master cylinder to make the feel of the front brake "firmer." There's a trade-off between progression and firmness. Personally, I'd rather have a little more progression and feel when braking with a small front wheel. So a larger cylinder is fine for me.
Next comes the only tricky part in the whole process. To remove the old piston in the master cylinder you will require some circlip pliers. The circlip that holds the master cylinder piston in place cannot be removed any other way.
Once inserted the adapted circlip pliers make removing and re-installing the circlip a breeze. Though make sure you get the circlip seated within its grove all the way around when it is re-installed.
I did not overhaul the front caliper. If you have time, it is a good idea to inspect and clean the front caliper thoroughly. Cleaning brake calipers is a job I hate but with rubber gloves and some solvent it's straightforward. Worst case, a brake caliper overhaul kit will enable you to replace all the piston seals and relube the pistons. Just take great care not to get the pistons stuck fully retracted or over-extend them (and keep your fingers outside the caliper. They are very powerful.) Top tip, a piece of wood to fit inside the caliper is very handy tool to keep the pistons in place.
Front Brake Upgrade - Discussion
I investigated methods for increasing the braking force on the front wheel. The most obvious is to remove the hydraulic connection from the Combi-Brake System, and to replace it with a double-banjo bolt connection to the front lever master cylinder. That way, all three pistons would be operated by the front brake lever.
The problem with this approach is that the standard master cylinder is designed to drive two front brake pistons, not three. (I assume that one is comfortable removing the CBS. Go down this route at your own risk.)
The solution is to consult hydraulic force equations to calculate the ratio and volume needed to operate the extra area provided by the middle piston. In short, I arrived at the industry standard solution of a 16x16 master cylinder to drive the three pistons with good brake "feel" at the lever. One could go to a larger master cylinder but that would result in less progressive braking.
I am not an professional or qualified engineer. If you want to disable the CBS please do your own hydraulic calculations. In principle, three pistons is perfectly safe provided you select the right master cylinder volume to give progressive braking. Proceed at your own risk!
Summary
The following front brake system provides upgraded brake feel and sufficient force: Honda master cylinder (12.7mm), stainless steel banjo bolts and fittings, brass washers, DOT4 brake fluid, stainless steel braided brake line (in this case Earl's), EBC HH brake pads, standard Honda steel brake disc.
