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Intermittent brake pressure

1996 Honda Accord 166k. Intermittently I lose pressure in my brake system. This means loss of pressure in the pedal, with the pedal traveling to the floor slowly when depressed. When I pump the pedal I get temporary pressure followed by loss of pressure. It seems to correlate with warmer outside air temperature (>80), though I can go for days without experiencing it.

When I had it in the shop recently for other work they looked for any leaks in the lines or master cylinder and found none. The only brake work I’ve had done was many months before the problem arose, so I don’t see a correlation there.

Any thoughts?

You are decribing classic master cylinder failure. You need to replace it, and you need a more competent shop.

Please get it fixed quickly; you are an accident waiting to happen.

That’s a classic sign of a brake master cylinder that’s leaking internally. No leaks outside the brakes system. It’s happening inside the brake system.

Replace the master cylinder and that should fix it.


I wholeheartedly agree that the symptoms point directly to an internal leak in the master cylinder. I also agree that you need a new shop.

Make this a fourth vote for replacement of both the master cylinder and your mechanic. Any mechanic who doesn’t recognize your exact description of a master cylinder with an internal leak is…not very competent.

Vote #5 here.

Thanks all for the feedback. The unanimity is comforting. It’s already in the shop.

Hopefully it is not in the same shop as previously!

Your original mechanic is not to be trusted, as his incompetence in recognizing this problem could have led to total loss of your brakes.