Re: Power brake booster engages on its own.

Posted by HH56 On 2015/3/20 18:08:10

I woud check the pedal and rod alignment first. If there is anything binding or out of alignment so the pedal can't retract fully when your foot is off then it might be activating the vacuum section. With the engine running so there is vacuum grab hold of the pedal and try to pull it back. If it moves at all and the problem goes away then check the carpet or that the screws on the floor plate are not loose or missing so the floor plate slipped or the rod is not at an angle between the pedal and brake unit. Less likely but has happened is the pedal bracket on firewall has developed some kind of bind.

If that doesn't seem to be the problem then something has happened internally like maybe a broken spring or failed valve or diaphragm.

EDIT: The 53 unit should only have the one hose connection on the side. Confirm that is correct and an earlier unit with two hoses hasn't been installed. If it does have two hoses make sure the vacuum supply is on the upper connection.