Jaguar World's Technical Advice Service

E knock off

- Ray Ingman

Q I have an uprated Series 1E-type 3.8, which I use hard on the road and extend its use to track days, both at home and across Europe. Modifications include Superflex polyurethane bushes, Gaz adjustable shock absorbers, Rob Beere Racing torsion bars, Harvey Bailey anti-roll bars front and rear, topped off by 6.5in competition wire wheels fitted with 225 Toyo tyres.

There is an intermittent problem with the brakes: I encounter disconcerting long pedal travel after travelling at high speed through any series of bends – particularly if I ride the kerbs to optimise my line. This occurs despite having fitted all new hydraulics, including an inline vacuum servo to the front line (replacing the Kelsey Hayes standard unit), Girling XJ/S2E rear calipers and three-pot BG Developments’ front callipers fitted to the original front uprights. I use Castrol SRF racing brake fluid, Goodridge braided hoses and Mintex M1144 fast road pads.

Derek Smalls

A All the improvements are excellent choices that should enhance the car and the enjoyment you derive from it without spoiling its intrinsic character.

However, the problem you have harks back to the original design of the stub axle, which is exacerbated by the increased loads that your modifications impose on the suspension. The phenomenon you are experiencing is known as ‘pad knock off’. The relatively slim stub axles, and hence hubs and discs, flex within the calipers under heavy load and consequently retract the pads back into the calipers. On the initial subsequent brake application, the first element of pedal travel returns the pads to their accustomed position in light contact with the discs – worryingly, having no effect on retardation. Under extreme conditions, you may even have to repeatedly tap the pedal before normal clearances and operation resume.