Joseph’s rear disc brake conversion
When driving on gravel you don’t get the weight transfer you get when braking on seal, and when rallying you also want a bit of rear bias to help kick the car sideways going into corners. By the time a codriver, tools, spare wheel and extra fuel are added, the rear brakes are working harder than the front! After pushing very hard on a stage with fast straights and tight corners in the 2008 Silver Fern I lost the rear brakes when the lining completely burnt off and disappeared.
So although I like to keep it in largely period spec, I converted Joseph’s rear brakes to discs! The conversion was easy to do and is shown below. The method can be used directly on the MGA or banjo axle MGB’s, or in principle on tube axle B/C/V8 or Midgets – the only difference being the actual disc used will need different dimensions.
The result was excellent, with the car recording 0.98g on 5 yr old rally tyres during the certification test. The pedal stays rock solid, no more adjusting – I had to adjust after every special stage before. The handbrake is also very good, and holds on our 1 in 3 driveway.
Here’s the details:
Calipers: MGF rear
Discs: 260mm Volvo (4.5″PCD, only change needed was to open out the holes to 1/2″)
Handbrake: Parking brake easily achieved by shortening existing cable slightly and attaching it directly to the caliper’s handbrake mechanism. Holds on 1 in 3 gradient so very effective! (Note that because of the intrusion of the fuel tank guard used in rallying, the caliper had to be mounted on the front side to get clearance for the handbrake cable. The handbrake idler is on top of the diff.)