brake issue, booster or electronic

[smoothrider]

my 2004 pathfinder has been having a strange brake issue. the brake goes low and hard. If I bleed the booster it gets better for a week... a day... or maybe next time we start the car. My wife drives it and she says sometimes it is bad for 15 min. and then it gets better. any ideas?

[Towncivilian]

Welcome to NICO.

Page BR-19 of the factory service manual has a brake booster check procedure for operation and airtightness. Follow it and see which test fails. Also check the vacuum piping (see BR-21) for cracks or other damage.

[smoothrider]

Well the booster is now doing nothing. the brakes are low and I hear a clicking by the e-brake (probably for the lights) but basicly all we have now is manual brakes and very low at that.

[Towncivilian]

Is the brake fluid level in the master cylinder between the "MIN" and "MAX" lines? Have you ever had a brake flush?

Did you inspect the vacuum piping?

[smoothrider]

I changed the master Cylinder about 4 months ago the level is max and I just took the pipe off to check it and it is good, vacuum hissed out of the booster when I removed it.

[smoothrider]

the brakes will not pump up they just stay low.

[Towncivilian]

Can you try to bypass the check valve in the vacuum hose to see if that changes anything?

[smoothrider]

I did blow through the hose, it only is possible one way so I would assume it is ok.
do you think it is not opening enough?

[Towncivilian]

I'm not sure, but if you can bypass it easily we may as well rule it out.

What brand master cylinder do you have installed? Why was the original one replaced?

[smoothrider]

could it be the brake cylinder is faulty again?/

[smoothrider]

ah we both came back at the same time with the same thought.. the original went bad just on our steet, my wife was very lucky. the replacement is an of-shore / rebuilt unit.

[Towncivilian]

It's certainly possible. Was the new MC bench bled before installation? I assume the brakes were bled after installation of the new MC as well?

[smoothrider]

Yes I bled the air out and the brakes worked great for at least 3 months and then slowly things have gotten worse.
this is not like when the MC went but I don't know, I have worked on my own cars since I was 16 and I am 57 now and I fix machinery for a living but this is one I have to say is strange. I haven't had to deal with the booster before.

[Towncivilian]

I'd lean towards a faulty master cylinder rather than brake booster, given that it's some remanufactured Chinese part. It sounds like the brake booster is working normally if vacuum is present and you checked the check valve. Perhaps look into a new master cylinder at RockAuto. I'd imagine Beck/Arnley or Cardone Select to be of satisfactory quality. If you order from RockAuto, be sure to use a 5% discount code.

I'm still unsure of the cause though - I've never experienced symptoms of either a failing master cylinder or brake booster, so perhaps you should try to get a second opinion somewhere.

[smoothrider]

Thanks for your input, it is great to another opinion on something like this. I will look at this tomorrow, perhaps I'll let someone else look at it this time. have a good night.