I got rid of the electric ABS unit of my newly acquired series 1 Mi16,and replace it with a standard 405 brake booster and master cylinder. Now the rear steps out on braking, I clearly need a proportioning valve. As this is a completely original car in mint condition, I don't want to put one in the cabin like we do in the rally cars. My mechanic tells that there is a mounting position for one on the right side of the rear end, so in theory they exist. Any input will be greatly appreciated.