1965 Chevy C-10.
Manual brakes.
Disk brakes on front - drum in rear.
Single brake fluid cylinder.
I think it would be safer to convert the single cylinder to a dual.
Question:
Is it necessary to replace all the brake lines when doing this or is it possible to just replace the cylinder and modify the lines at the cylinder? (The lines seem to be in decent shape).
I would replace the lines if for no other reason than to limit the number of unions in the lines. When the master cylinder is replaced you will now have two lines running to the proportioning valve. The proportioning valve regulates the pressure to the rear lines thereby helping reduce rear wheel lock-up. It also contains the switch for your in dash brake warning light. The new valve will have two inputs and two outputs. The plumbing most like will require numerous small pieces and fittings to match the old lines to the new valve. Each fitting has a potential to leak so the fewer the better. If you check some of the old truck restoration sources like LMC, Ecklers, Classic Industries you may find prebent lines in regular or stainless steel. They are more costly but the lines are bent and flared perfectly you will have to decide if the convenience is worth the cost. While you are looking for kits consider an adjustable valve. It will allow you to tune the brakes for minimal lock-up.
