I have a 1974 F250 4x4 and recently developed a leak in the metal brake line that goes to the rear tires. Does anyone know what dia. this line is? I want to purchase the longest straight piece available at the auto parts store but I need to know the dia. I tried to measure it with a pair of dial calipers however the outside is so rusted I can't get a good reading.

 

3/16" is standard. Over the years it could have gotten changed to a larger diameter though. Best bet is to get a tubing cutter, cut out a chunk of the line, and bring it in to match up.

 

OK, thanks! I'll buy a piece and try it. Another thing, I changed this truck from drum brakes on the front to disk and since this conversion the brake pedal is soft. No matter how much I bleed them, I can't get a stiff brake pedal. Is it possible this requires a different proportioning valve?

 

It does require the correct proportioning valve, and may also require a different master cylinder.