Contents of the Grimeca semi-hydraulic kit, plus the bag of hardware.

Last post we talked about the options available to vintage Vespa owners looking to upgrade their front brakes from the stock drum configuration to a disc brake.

In this post I’ll be removing the existing front hub in preparation for the installation of one option – the Grimeca semi-hydraulic kit. Everything here should take no more than half-an-hour with the correct tools at hand.

The kit is available directly from the manufacturer, Germany’s S.I.P. Scootershop or US importer Motorsport Scooters if you prefer not to deal with international shipping.

I purchased the 20mm kit ­– the appropriate front fork dimension for my 1985 model PX150e.

How's your German?

As you can see from the photograph above, unless you’re fluent in German and Italian you’re out of luck when it comes to the instructions. There is however a somewhat helpful series of line drawings that will allow you to get a sense of alignment of the set up on your front hub.

Thankfully, once you begin to play with the parts, very little are interchangeable so it’s fairly clear what goes where.

Getting familiar with the kit
The kit comprises three key parts and some additional mounting hardware:

1. The back-plate. Unlike the drum back-plate, this is a relatively small design providing a mounting spot for the brake caliper.
2. The front-hub/disc. Arrives as two pieces.
3. The brake caliper/remote master cylinder. These two pieces should come fit as one and loaded with brake fluid. Pulling on the actuator arm of the master cylinder should noticeably squeeze the brake caliper.

It’s worth taking a few minutes to “dry-fit” the kit together away from the bike so that you understand it. But be very careful not to slot the hub front plate with speedometer gearing down onto the back-plate at this stage. The rubber oil seal is designed to click into place and is ideally only fitted once.

If you do click them together (as I did), they will prize apart but check to make sure you didn’t damage the rubber seal in the process. The seal includes a spring-like metal ring that I had to throw out after the mistake. Thankfully this is not a mission critical part.

You may also find that the brake caliper is closed tight preventing you from gripping the disc. If this is the case, simply insert a large flat bladed screwdriver between the brake pads and give it a gentle turn. This will force open the jaws of the brake.

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 removal, suspension removal.
• 7mm, 8mm wrenches for the cable pinch-bolt, speedometer retention plate.
• Circlip (AKA snap ring) pliers. (Somewhat of a specialist tool, but the job is nearly impossible without them.)
• A pair of pliers, ideally needle nose.
• A Philips screwdriver for the headset dis-assembly.

Removing the existing front hub
You’ll need to remove the front hub in the same way that you would typically tend to the front brake shoes. Do the following before you remove the wheel:

1. Remove the grease cap cover.
2. Remove the existing cotter pin. A pair of needle nose pliers helps here, and a few taps with a small hammer may be necessary.
3. Remove the castellated lock cover exposing the front hub nut.
4. Remove the hub nut with your 22mm socket wrench. Keep a steady hand on the wheel while you do so. The nut may need some persuasion to turn, which is why it’s helpful to do this before you remove the wheel itself.
5. Remove the washer.

You are now ready to pull the front hub. Depending on when the last time this was done, it may also need some persuasion, and it’s another reason to leave the existing wheel on. If grabbing and rocking the wheel slightly doesn’t work, work around the tire with a few hits of a hammer to shock the hub loose. Hitting the rubber ensures you free the hub without damaging the metalwork.

After the front hub has been pulled from the back-plate, and the wheel removed.

Removing the shock absorber
To be able to remove the back-plate, you’ll first need to disconnect the shock. Without a friend to help you, it’s difficult (and potentially dangerous) to compress the shock to get at the two mounting bolts that mount it to the back-plate. The simpler option is to disconnect the shock at the top where it connects to the front fork underneath the front fender via two 13mm bolts.

Once loose, the shock should fall free, allowing you much easier access to the back-plate and speedometer drive. At this point you can easily access the two lower 13mm bolts and remove the shock from the back-plate.

Freeing the back-plate
Before removing the back-plate from the access, you’ll also need to disconnect the existing brake and speedometer cables:

1. Disconnect the existing brake cable from the brake actuator lever on the other side of the hub.
2. Unbolt the plate that secures the speedometer cable in place on the back-plate and pull the cable free.

Freeing the front brake cable from the drum brake actuator.

Removing the back-plate
Now that the back-plate is disconnected from cabling and the suspension, you are clear to remove it:

1. There will likely be plenty of grease inside the hub on the spindle. Clean as much of this as you can with paper towels or shop cloths. Under the gunk expose the circlip. This is what retains the back-plate on the spindle.
2. Open up the circlip with a pair of circlip pliers and remove it. At this point the back-plate should immediately come loose. If you have a tip to remove circlips without circlip pliers, let me know. I bought a set of pliers with interchangeable pincers for less than $10 and they were a lifesaver. Set the circlip aside. You’ll need this during re-assembly.
3. Don’t pull the back-plate just yet. Behind the circlip should be a spacer washer. It’s designed with an off-round aperture so that it won’t spin freely. Remove the washer with a pair of pliers. Or, if you can’t get at it, remove the back-plate and then tap it free of the grease. Again set it aside – you’ll be reusing it.
4. The back-plate should now be removable from the spindle. Behind the back-plate should be a rubber and/or metal grommet. Note their order. Again you’ll need these on your new set-up. These allow the suspension arm to rock free of the back-plate.

The back-plate removed and the spindle cleaned. Note the circlip and flat washer on the floor. The rubber grommet is still on the back of the spindle.

Clean-up
With the back-plate disassembled, use this opportunity to collect up the circlip, flat washer and grommet from the existing axle and clean them of the old grease. Also clean the axle itself.

Inside the speedometer drive hole on the old back-plate, use a pair of needle nose pliers to carefully remove the rubber grommet, followed by a brass insert and finally the plastic speedometer pinion gear. All of these elements will need to go back into your new disc brake. If the pinion gear is badly worn, it’s worth replacing at this point.

Congratulations, you are now done with the complete dis-assembly of the front hub. In the next post we’ll talk about installing the new disc set up.

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