I now need new rear brakes to match the Wilwood Tiger front brake kit – 11.75” rotors, radial callipers with 4 x 1.75” pistons, and Wilwood BP-10 pads with a nominal friction rating of .046.
This is not my first go around with rear discs, and I have learned a bit more since my 1980 approach of simply finding something that will fit on the rear, while using a proportioning valve to try and match the front brakes. Complicating the issue is weight transfer and all that entails, tire grip, tire size, pad coefficients, pad area, calliper piston area, rotor OD, fore/aft car balance, pedal ratio, proportioning valve slope, master cylinder bore, deceleration rate, centre of gravity height, ............ This latest rear brake design attempts to take these issues into account.
Dan Walters wrote in Tiger Tales several years ago about using 04 Mustang Cobra rear rotors, and a 38mm single piston rear calliper. I looked at different brake bias combinations, and pad coefficients, to match the Cobra rears to the Wilwood fronts. With .55 performance pads, and a .37 slope proportioning valve, the Walters Cobra design, would match the Wilwood front kit. If one wants to use more common .40 street pads then more clamping force is needed at the rear. Size matters, and the larger 93-98 Lincoln MK Vlll single 45.2mm piston calliper gives 40% more brake torque than the 38mm Cobra calliper on the same 11.65 OD Cobra rotor. This is a good match to the Wilwood front kit with .046 pads.
A .75” bore, dual circuit master cylinder is used to keep the hydraulic pressures up and leg pressure down as there is no servo in the system. Nothing new here, and I used one from a Ford Courier pickup, with a .37 slope Wilwood proportioning valve. With the .75 master, leg force will be acceptable using the stock pedal ratio - a higher ratio pedal would be better.
The system is fitted using the Lincoln callipers now but I am now redesigning the bracket to rotate the calliper downward to gain a bit more calliper to frame clearance. I have 15” wheels and these brakes will not fit using the stock 13” wheels.
The only bespoke part is the mounting bracket to fit the Lincoln calliper. Machine work is required to bore the hub on the Cobra rotor, drilling the rotor for our stud pattern, and facing the stock hub to insure it is flat.
