So now I'm running the AP rear calipers, I need a handbrake solution. Specifically I need a mechanical handbrake solution to satisfy the MOT requirements.

 

A popular choice is the seperate 'spot' handbrake caliper: an additional, small, single pot caliper is mounted on each side which can be mechanically operated by the handbrake cable in the normal fashion. There is a design problem with this approach but it can be worked around.
 
The spot caliper can not 'float' as intended, due to a lack of space for the correct bracketry between it and the 13" wheel. This means that in order to operate with a reasonable degree of force, it must be adjusted to drag against the disc slightly. Obviously this is not sensible for day-to-day operation.
 
To get around the problem, the spot calipers are fitted and adjusted/used solely for the MOT.

 

I've opted for a combined hydraulic race/mechanical handbrake caliper from Wilwood, based on their existing 4-pot Powerlite range. The mounting dimensions and disk offset make it a direct-swap for my existing AP calipers.

 

 

 

The calipers are a very close fit within a 13" wheel (in fact the handbrake arms foul the wheel unless modifications are made to increase the clearance).

 

The caliper hydraulic inlets are an American 1/8"-27 NPT fitting. 1/8 NPT x 3/8 UNF fittings are needed to adapt to the Caterham brake lines (or there's a useful 1/8NPT to swaged collar fitting which allows connection to a new piece of braided brake hose)

 

The calipers have been succesfully installed and tested. Both the handbrake and hydraulic brake functions work really well after a bit of fettling:

 

90 degree inlet fittings have been used for the hydraulic lines to get good clearance for the watts linkage and to convert the 3/8 UNF brake lines

 

The handbrake arms have had the tops angle-ground off to reduce their height

 

The mounting brackets that sit between the AP caliper and DeDion ear to locate the brakes in the right position on the disk need modification - the top 'deck' of the bracket needs skimming by about 5mm to drop the caliper on to the disk and reduce it's height. The outer side of the valley, in the middle of the bracket needs widening to accomodate the body of the dropped caliper and to allow the inner pad to move without binding

 

Initially I didn't widen the valley in the middle of the bracket. Everything appeared to work but the inner brake pad was not able to move freely, causing uneven clamping and causing the rear brakes to stick because the pads could not move back again. After this last alteration they work well.

 

The Caterham handbrake mechanism had the bottom clevis pin and pulley bracketry removed. The hole through which it used to mount was enlarged with a size 10 drill. This allows the Powerlite handbrake pulling bar to be accomodated. The end of the handbrake cables pass through holes drilled at either end of this bar.

 

The supplied springs which keep the handbrake arms apart were over-sized and sometimes brushed the inside of the wheel so some smaller diameter ones were sourced which were much more suitable.