Installing a semi-hydraulic disc brake on a P Vespa Step 3

Last post we talked about preparing your existing fork to receive the new semi-hydraulic set up. Now we get to work with installing the new brakes.

Note: Don’t reconnect the shock absorber until later in the process; otherwise it’ll be tough getting at the speedometer gearing. While installing the back-plate and front hub the spindle should be hanging loose on the fork.

Assembling the tools
You’ll need the following:

• 5mm Allen key.
• Torque wrench.
• 22mm socket for the front hub nut.
• 13mm socket for the wheel replacement, suspension replacement.
• 7mm, 8mm wrenches for the cable pinch-bolt, speedometer retention plate.
• Circlip (AKA snap ring) pliers.
• A pair of pliers, ideally needle nose.
• A Philips screwdriver for the headset bolts.

Installing the new back-plate
The orientation of the back-plate should be clear and while considerably smaller than the old back-plate, attaches to the spindle in the same manner:

1. Ensure that the existing rubber grommet and any other washers or similar hardware that sat behind the original back-plate go back on the spindle first. This buffer allows the back-plate to move independently of the suspension.
2. Next is the back-plate itself.
3. Followed by the flat washer, which is designed to only fit a certain way so you may need to use your needle-nose pliers to line it up and bed it down.
4. Finally the back-plate and hardware are secured in place using the original circlip. You should feel a definitive click as you push this down into place and it should allow the back-plate to rotate freely but not move forward or backward along the spindle.

Adding the back-plate.

Reconnecting the speedometer
This is why I recommended not connecting the shock earlier. Getting at the speedometer gearing can be a pain if the shock is obstructing your view.

Add the components to the base of your speedometer cable in the following order: metal retention plate (teardrop shaped,) rubber grommet, brass bushing, and plastic pinion gear. Check the pinion gear carefully. Only one end has a square hole, which is designed to plug on to the end of your cable. Now add some grease to the pinion gear.

The order you just added the components to the cable should mean that as they push down into the back-plate, they should go down in the reverse order: pinion gear, brass housing, rubber grommet, retention plate. Finally bolt down the retention plate, which squeezes the grommet and in turn locks the cable in place.

Reconnect the speedometer gearing with the suspension loose from the frame to give you the room to work without obstruction.

You may need to lift the back-plate slightly to relieve tension on the cable to allow you to bolt down the retention plate which is a little awkward but still much easier than trying to do this with the shock absorber in place.

Note: you may also find that the original brass bushing is too long for the new back-plate. If this is the case order a replacement one designed for the Millennium PX series.

Reconnecting the suspension
With the speedometer back in place, reconnect the shock absorber starting with the lower two 13mm bolts. The 13mm bolts that it connects to at the top do sit loose in the bracket which can make it tough to add the washer and nut. To combat this, try twisting the shock slightly so that the top plate grips the bolts as you add the hardware.

Connecting the disc to the front hub
Connect the disc to the front hub using the five Allen screws and lock washers provided with the kit. Make sure that the disc is traveling in the correct direction. It has an engraved arrow to indicate this, and it’s important to get this right for optimum braking. Hold the disc up against the back-plate on the bike to double-check the direction. In my case it was unintuitive because the disc needed to be placed arrow-side-down against the front hub to be correct.

Before you push the new front hub and disc onto the spindle and back-plate, use a liberal amount of grease to lubricate the spindle and the speedometer gearing on the inside of the hub. Needless to say, avoid getting grease, oil or any similar substance on the disc itself.

Secure the disc with the Allen bolts and grip washers provided. Grease the speedo gearing and double-check the direction of spin.

Adding the front hub to the spindle
Pushing the front hub onto the spindle should provide a definite click as it locks onto the back-plate. You shouldn’t be able to pull it loose except by force.

Finally, lock the new front hub down on the spindle in the same manner as the old front hub. Add the washer and tighten down the 22mm hub nut, followed by the castellated cover, and finally the cotter pin. Whenever removing either one of the hubs for brake inspection, always replace with a new cotter pin. This small pin is key to your safety. You can pick them up cheaply at most hardware stores. I also like to add a little grease to the nut and pin before replacing the hubcap to help fight any potential rusting. Finally replace the dust cap.

Removing the old brake cable
The kit comes with a new brake cable. I personally found that while the new cable outer was useful for the new disc because it is shorter, the cable itself was too short for my needs. Depending on the P-series bike you have, you may not have this issue.

No matter which set-up you have, this is the ideal chance to renew your front brake cable.

First access the inside of the headset by removing the four bolts under the headset with a Philips screwdriver. Gently lift on the top of the headset. There should be enough play in the speedometer cable to allow you to lift the top up and slightly to the side allowing you to access the inside of the steering column. If it doesn’t come free, try pushing on the speedometer cable from the fork side, which should push up and free the headset.

Next, remove the old cable inner and outer. I found that the easiest way to do this is to pull on the barrel-end of the cable at the brake lever with a pair of pliers and pull the entire cable out. In my set up the cable runs through both the main cable outer, the front brake switch near the brake lever and a three-inch distance of cable outer to the brake lever. You can find more information on this in a past post.

With the cable itself free, do the same with the cable outer and pull it through the fork and out of the top of the steering column.

The new cable outer in place, and the new cable about to be threaded through.

Adding the new brake cable
Take the new cable outer supplied with the kit and insert it in the hole at the lower end of the front fork near the hub and push it through. There’s only one way for the cable to go, which is out of the top of the steering column, so it won’t get lost on it’s way to the light. This new outer is designed to position your front cable in the best position for the new disc brake actuator/master cylinder.

Now add your new cable. Thread this through top-down from the brake lever, through the short length of outer and brake switch as appropriate and then down through the new cable outer. It will then come through at the lower fork. Ideally you need a couple of inches to give you enough to play with to hook up the disc. If there’s very little cable coming through, then consider a longer standard cable than the one that came with the kit.

Whenever I add a new cable I also like to add a small amount of grease to my fingers and run the cable through them to add some lubrication before inserting in the outer but with most modern Teflon cable outers other scooterists argue this isn’t necessary.

Go ahead and close back up the headset.

Adding the brake Caliper/master cylinder/actuator
With the new brake cable waiting for a brake it’s time to turn your attention back to the fork to hook up the new brake caliper and master cylinder/actuator.

The caliper itself bolts to the back-plate with the supplied hardware. Connect this up now and let the master cylinder hang loose. As mentioned in a previous post, if you need to open up the brake shoes, do so by inserting a large flat-bladed screwdriver and turning a quarter turn or so.

Bolting the caliper to the back-plate.

The master cylinder is connected to the front fork with the supplied o-ring grip. Make sure when you add it that you have enough room to allow the actuator lever at the bottom to move without hitting anything (you don’t want this to jam at speed) and also tighten the grip so that the bolt won’t touch the tire when the wheel is returned to the hub.

The master cylinder/brake actuator attached to the fork and ready for the cable.

Hooking up the new brake cable
Congratulations, you’re almost there. But this last step is the one that may take some back and forth. Don’t add the wheel yet. You’ll want to test the braking first.

Give the actuator on the master cylinder a squeeze with your fingers as you spin the front hub to test the brake. This will also give you a sense of how far the actuator needs to travel to clamp the brake down. It’s likely that your brake lever at the headset can only pull the cable a short part of the total throw, so this is what your aiming for as you tighten everything into place.

The kit comes supplied with a V-shaped spring. This is designed to sit between the jaws of the actuator. Thread the brake cable through the top of the actuator, through the spring and into a pinch-bolt (supplied) in the lower jaw of the actuator.

At this point pull the cable through as tight as you can to remove any slack front the lever at the headset. It’s useful to have a friend do this with a pair of pliers while you turn your attention to the bolting down the pinch-bolt. Or use a forth hand tool if you’re working solo.

The trick is to engage the actuator as much as you can before it jams the brake and then tighten down the pinch-bolt. This way, pulling on the brake lever is only pulling the useful part of the throw distance of the actuator, the part that does anything.

It’s okay if the brake is grabbing a little in the off state so long as you can turn the wheel relatively freely.

You are now hooked up and ready for some testing. Now go ahead and put the front wheel back on your new hub.

Everything installed and ready for testing.

Testing
Test the new brake first by walking the bike forward without power. Gripping the front brake lever should feel firm and provide some decent resistance without obvious slack. You should also feel it solidly grip the brake and ideally lock the wheel so that pushing the bike dives the front shock but won’t allow the wheel to turn.

If the scoot is tough to push with the brakes off, ease off on the tension on the cable with the pinch-bolt. If the brakes are slack in any way close up the slack.

Make sure you feel confident that you have a good brake before getting on the road. If you can’t get a good brake just by pushing the scooter by hand, you’ll never get one at speed.

Finally, it’s time to get out on the bike. Take it really easy at first until you’ve gotten a good sense of the effectiveness of the brake. Adjust as necessary, and after a couple of days adjust again to account for any initial cable stretch.

The semi-hydraulic brake should feel significantly better than the original drum set up. If it doesn’t then continue to tweak the tension at the front actuator, or consider bleeding the hydraulic components (we’ll cover this in a future post.) You should also find that after a couple of days of riding the brakes will “bed-in” and provide a better grip than the initial testing.

Good luck, and brake safe.

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