Brake pedal going to the floor after startup

GORDON CHUMWAY

MEMBER
2005 NISSAN XTERRA
4.0L
V6
4WD
AUTOMATIC
140,000 MILES

I had a soft brake pedal and bleeding the system did not help. I put on a new master cylinder and bled the system (bench and at the wheels). Seems good but as soon as I start the ignition and I push the pedal it goes right to the floor. Bled again and again and same result. Put on another new master cylinder and same result. Tested the master on the bench and it seems fine (good flow on both lines). I am stumped, no leaks anywhere and I do not know what to do next.

Thursday, November 1st, 2018 AT 5:50 PM

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

If the pedal is going to the floor then we have a leak or air in the lines. There are no other causes of this as the pedal is dropping because it doesn't have proper pressure against the pedal due to the system not being sealed.

Here is a guide that helps with this:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

The way to test this and find the issue is to cap off the master cylinder when on the vehicle and make sure there is a hard pedal. If not the master cylinder is the issue.

If there is a hard pedal then we need to put each line back on one at a time until the pedal is soft again. This will tell us what section of the system is leaking pressure or has air in it. At that point, crimp off the rubber lines at each wheel and narrow it down even further.

Let us know what you find with this and we can go from there.

Thanks

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