Disc brake conversion kit for Volkswagen Beetle

What the translation really achieves

A drum in good condition brakes properly the first time. Where it falls short is when you have to do it again: it traps heat, and after a few hard braking manoeuvres on a downhill stretch, the lining loses its bite and the pedal travel increases. A disc is exposed to the air, so it dissipates heat and retains its effectiveness.

• Endurance: this is the main benefit, and it is spectacular during sustained use or in the mountains.
• Consistent braking feel: a disc brake responds proportionally to the force applied, whereas a drum brake has a self-seizing effect that makes braking less linear.
• Performance in the rain: a disc wipes itself clean with a single rotation of the wheel, whilst a drum retains water.
• Maintenance: immediate visual inspection and replacement of brake pads without removing the hub.

However, the conversion does not necessarily shorten the cold stopping distance of a light vehicle: on the first application, a good drum brake performs almost as well. It is with repeated use that the gap widens.

What a complete kit should contain

• Discs – solid, grooved or ventilated, depending on the intended use.
• The calipers and their brake pads, along with the brackets or yoke assemblies that position them opposite the disc.
• The mounting brackets on the steering knuckle or axle, which are the truly specific components of the kit.
• The appropriatehoses, fittings and, in some cases, a brake manifold, as the location of the connection point may vary.
• The fasteners to the required strength grade, bearings and hubs if the installation requires them.

Discs sold on their own are also available, to replace worn parts in an existing conversion. Make sure you check what you’re buying: a disc on its own won’t convert anything.

The bore pattern: the dimension that determines everything

The bolt pattern of a hub is specified by two figures: the number of bolts and the diameter of the circle on which they are arranged, in millimetres. A conversion kit dictates its own bolt pattern, and this is not always the same as the original.

The consequence is straightforward: if the kit changes the bolt pattern, your current wheels won’t fit, and you’ll need to factor compatible rims into your budget. Some kits deliberately adopt a more common bolt pattern, precisely to broaden the choice of rims; others retain the original bolt pattern so that nothing else changes. Also check the offset: a brake caliper may rub against the rim, and this is something you’ll only discover during a test drive. Finally, make sure the kit covers both wheels on the same axle: converting just one side will throw the braking balance off, which is dangerous.

How the conversion affects the rest of the braking system

A disc and a drum do not operate with the same hydraulic characteristics. A drum has a self-squeeze effect that amplifies the braking force; a disc does not and requires greater pressure. Changing one without considering the rest will cause the braking system to become unbalanced.

• The front-to-rear brake force distribution is altered. With a rear conversion in particular, a suitable brake force distributor or limiter is often required.
• The master cylinder must be able to supply the required volume: an unsuitable diameter results in a pedal that is too stiff or has too long a travel.
• Power-assisted braking may be desirable on a vehicle that did not previously have it, depending on the weight and intended use.
• The parking brake, if it previously acted on the rear drum, must be adapted: not all rear conversion kits include this function, and it is a point checked during the MOT test.
• The brake fluid must be completely replaced and the system carefully bled.

Modifying the braking system may also affect the vehicle’s roadworthiness: check the applicable regulations before starting the work, and have the result tested on a brake test bench.