1960s 1960 hard brake pedal

[60eldo]

When i apply my brake sometimes not always i get a hard brake pedal. Would that be the check valve or the booster. How to test them?

[TJ Hopland]

If you have a poor running engine with poor vacuum there could be times there isn't enough vacuum to properly operate the booster.  IF the check valve or booster is bad that just increases the chances of an issue because you may not have the reserve built up to operated the booster if/when there isn't a lot of engine vacuum available which is normal under certain operating conditions.

Also if the booster is leaking that can be a significant vacuum leak which could be part of your other issues.  Seems like people brought that up a time or two troubleshooting your issues.  Did you ever do any testing related to the booster?   

[Gabe Davis]

Take a look at the bottom of the vacuum reservoir too. My 59 had some pinhole rust spots. I ended up putting a booster/master from a 68 in it which has the reservoir built in and I bypassed the original. But a small vacuum leak could be causing issues.

[60eldo]

 I disconnected the booster and plugged the line at carb, then checked vac.,,,,no change, also put in a different reserve can,,,no change. Going today pick up new check valve, try that. But brakes were good after the new engine was put in, then after about 400 miles, got the hard pedal. so i dont think its engine vac,,maybe im rong