I have recently bought my daughter a 1993 Honda Civic Auto 1600, it has an intermittent issue with the brakes, at the traffic lights while holding pressure on the brakes they sometimes fade (the pedal drops) this is as I said an intermittent fault as it is ok one moment and the next it isn't, when I first noticed it I thought the MC was bypassing but because it comes and goes I am not so sure? Does anyone have a similar issue or can relate a possible cause and suggestions on a repair. My first instinct is to overhaul the MC or possibly change it with new.

 

Are you loosing fluid?

Before change anything, check for fluid leaks. i.e. calipers, brake lines, rear drums or calipers, also lift the carpet in the driver side and check for fluid in the floor behind the pedals.

 

No fluid leaks visible or fluid loss from the reservoir.

 

Normally the MC's works fine or went bad, not intermittent but all is possible, maybe can be a start to going bad seal in the MC the culprit.

If you have access to a vacuum pump perform a test in the brake booster. Maybe a small leak in the diaphragm is affecting when you left the pedal pressed for long time.

 

Hmm I don't have access to a vacuum pump, my first thought was the diaphragm in the booster, but because it is intermittent it has confused me, the strange fact is when you apply the brakes it is a solid pedal until you hold pressure for a while under load, but as I said it does point to a MC issue, I may have to bite the bullet and take it to a Brake repair Specialist to diagnose.

 

sounds like it could be a bad rear brake cylinder starting to go, did you check inside the boots and all?
wouldn't hurt to check either way