I'm gather up some parts to convert my '65 122 single circuit brakes to dual circuit brake system.

I want to leave the rear drum brakes alone, and just add a second proportioning valve (replace both valves with similar units).

My questions is adding 4-piston calipers to the front. I have located a '70 1800 that I can get the brake lines, brake junction boxes, proportioning valves, calipers, mounting brackets, backing plates, etc.

I looked up the parts between the '70-'73 1800, '69 -'70 (B20)122 and the '65 (B18)122, and it seems that the steering knuckles are the same between the three models, the wheel hubs/rotors are the same between the B20 and B18 122, and the calipers/mounting brackets/backing plates are the same between the '70 1800 and the B20 122.

There is a difference between the wheel hub/rotors of the '70 1800 and the B20 122. The wheel hub/rotors from the 1800 are taller than the ones from 122s (B18 and B20).

My plan is to use the existing steering knuckle, wheel hub, and rotors (to keep the bolt pattern the same between the front and back), and replace the backing plates, caliper mounting brackets, calipers, and the plumbing from a 4-piston 1800 setup.

Has anyone converted their 3-piston caliper setup (single circuit) to a 4-piston caliper setup (dual circuit)? Does anyone see a problem with this conversion as described?


The difference between the 4-caliper 1800 wheel hub/rotor and the B20 122 wheel hub/rotor kind of bothers me. I'm planning on doing a fit test on my other inoperable 122 ('66) to see if the 4-piston backing plate/mounting braket/caliper will actually fit onto the ealier 3-piston 122 as planned.

I also wonder about using the rear disc proportioning valves on the rear drums?

Paul