Only period modifications used in rallying on the particular make and model of car are permitted for both Category 1 and Category 2 Historic Rally Cars. Modifications are only allowed if they were available before 1.1.68 in the case of Category 1 and before 1.1.75 in the case of Category 2 Historic Rally Cars.
Category 3 run to the specification as shown on there homologation form.

Master Cylinders.

Single outlet master cylinders may be replaced by a Tandem or Twin cylinder arrangement.

The fitting of a dual master cylinder or any other type of device providing a simultaneous action on all four wheels and divided action on two wheels is permitted, providing the original brake pedal and pivot point are used and they cannot be adjusted to effect brake balance by either the driver or co-driver when normally seated in the car.

Brake Servo.

These can be added or removed.

Brake Discs.

The use of grooved or cross drilled brake discs are not allowed unless it can be proved it was as used in period.

Brake Calipers.

Brake calipers must be of the same material and dimensions as used on the original items. The number of pistons must remain the same. The mounting points and there locations must be the same.

Flexible Brake Hoses.

These can be replaced by Aero quip type of flexible pipe and fittings.

Brake Lines.

These may be run internally inside the vehicle to avoid the risk of fracture, or damage etc.

Brake Compensating valves.

Adjustable brake biasing valves are not allowed unless it can be proved it was used in period.

Friction Material and Brake fluid.

The make and specification is free.

Hydraulic Handbrake.

Hydraulic Handbrakes are generally not allowed unless documented evidence is provided to prove they were used in rallying to the make and model of veicle in period. There must also be a mechanical means of hand brake operation fitted as well.