[Lynn]

Actually, on the 69, I believe the check valve is underneath the brass flare nut mating surface.

Here is how to diagnose. Get the front brakes warm, then get the front wheels off the ground quickly. While an assistant tries to rotate one of the wheels, crack the line at the master cyl, being careful to catch any fluid. If the wheel suddenly rotates easily, then you found the problem.

To remove the check valve, you will need to take the line loose from the master cyl. You will see a pressed in fitting in the master cyl. Screw a sheet metal screw into the brass fitting about a full turn. Then pry the fitting out with a pair of dykes (yeah, now I know we have "high and hard" and a pair of dykes - oh well). The check valve is just plastic and can be removed now, as it is held in by the brass fitting. You can re use the fitting.

If I remember correctly (been 30 years, you know) the old rebuild kits come with the check valves, and the instructions say to discard for disc brake cars.

If the wheel doesn't rotate easily when you crack the line, then you probably have a piston caliper problem, which is very unusual on a GM car since the pistons are metal. Now, those damn fords, well this happens all the time because of the composite pistons which swell over time from, you guessed it, exposure to brake fluid.

Hope this helps.