Brakes - Part 1 - Decision Time

My original intentions for the brakes on Project Snake were always to refurbish and reuse the original brakes from the donor car.  As Jon at AK told me "if they are good enough to stop a 2.5tonne Jag, they're good enough for a 1.4tonne Cobra".

When I sourced the donor parts from Simply Performance, they suggested that getting the biggest brakes possible from the outset would be the best path to take.  I wanted vented discs on both the front and the rear and Ben at Simply Performance suggested using a car with the larger XJ twin-pot calipers at the front.  Seemed like a good suggestion at the time and that is what I went with.

So the brake discs and calipers I got with the donor vehicle are summarised below.

The eagle-eyed amongst you will spot that the rear disc diameter is larger than the front, which is unusual.  Usually, under heavy braking and weight transfer towards the front end of the car, it is the front brakes that do more work in bringing the car to a halt, and hence traditionally they are larger.  I assume that the use of the twin-pot caliper at the front provides enhanced braking performance over the larger disc / single-pot caliper arrangement at the rear and allows a slightly smaller disc to be used. But who knows what was in the mind of those engineers at Jaguar?

It seems however that those twin-pot front calipers are a bit of an enigma.  Whichever of the usual Jaguar part suppliers I looked at to try and find service parts for these calipers, they didn't seem to exist.  Even typing my donor car VIN number into various parts websites still kept on bringing up the single-pot caliper.

Twin-pot Front Caliper

Single Pot Rear Caliper

Disc Thickness (Thicker Front on Left)

Disc Diameter (Smaller Front on Left)

Front disc 10mm smaller diameter than Rear...?!

I contacted Ben at Simply Performance and he suggested that maybe if I measured the piston diameter in the caliper then I might be able to find suitable replacement piston/seal kits from another caliper option.  No joy there; the diameter of the twin-pot pistons is smaller than any of the other standard front (or rear) pistons in the various calipers over the years.

I did find a couple of places online that claimed to be able to refurbish the calipers, but given my failure to find any semblance of service parts for these unicorn calipers, I wasn't convinced.  I did eventually discover that Ward Engineering in Colchester, which is a specialist in the supply of reconditioned Jaguar axles and brakes, did offer a reconditioning service for the twin-pot calipers.  However, by then, my plans had taken a slight change.

Switching from an LS3 engine to an LS7 with close to 660hp got me thinking that, despite Jon's adage above, rapid and stable deceleration was going to be a top priority.  The oddity of the smaller diameter front discs compared to the rear on my donor vehicle was also starting to perturb me; I didn't want any unexpected twitchiness under heavy braking.

So when the UK taxman gave me a very unexpected but very well received tax rebate, my mind was made up.  It was time to buy an AK Big Brake Upgrade Kit!