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2015 Nissan Pathfinder

Legend:

  • DF: Driver Front
  • DR: Driver Rear
  • PF: Passenger Front
  • PR: Passenger Rear

About 2 months ago I took it in for a safety inspection (bi-annual safety inspection is required where I live) and the PR pads were over 90% used but the other 3 pads were fine. I got the pads changed so I could get the pass on the inspection but the fact that one caliper was going through pads like that made my think about inspecting and replacing any worn out parts.

Rotors are less than a year old.

On the PR the caliper came off easy (none of the pins were seized) and after some research I decided to rebuild it with new seals ($8 vs $120 for a new caliper).

On the DR one of the pins was not easy to get out so I changed the whole caliper.

I saw a bleeding method of using a bottle and hose where one person can do the bleeding as long as there is fluid in the bottle so that when you let off the pedal it can only suck fluid back instead of air. I tried this method and found the pedal soft and the vehicle didn't stop well in the driveway. The next day I got a help to bleed it with the 2 man method. I was at the bleeder screw. I saw air bubbles coming from the new caliper. I bled all 4 brakes according to the service manual for this vehicle: PF, DF, PR, DR. I went through a half bottle and the fluid in the reservoir looks new and is full.

After bleeding I test drove and found it stopped very well in the drive and on my country roads at high speed. I felt confident I had resolved the issue.

I was going to pick up a friends trailer in town but as time and the drive went on I got more worried about the brakes. While driving about 50% of the pedal does nothing then I can feel the brakes slowing me down. If I slam the brakes the vehicle stops very quickly. So to make it clear I'm not having issues stopping the car.

When I'm sitting at a stop or light I noticed the thing that caused me alarm: The pedal slowly sinks to the floor. If I pump the brakes it gets a little stiff then sinks again. It might be just nerves but I think I noticed it lurching forward ever so slightly (especially with the AC on and the rpms slightly higher to turn the compressor).

So to sum up when I am driving along and I need to stop I can stop quickly if needed, but when I'm stopped at a light the pedal travels and feels spongy.

I've read a few posts on Nissan forums and there is never a resolution, just a large bill of replacemnet parts. Someone even suggessted removing the ABS fuse. I'm lost on this one.

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If you are certain that you are not leaking brake fluid anywhere, then your master cylinder needs to be replaced or rebuilt. Brake fluid is leaking past the seal within the master cylinder from the high pressure side to the reservoir side of the seal. This doesn't affect emergency braking because the leak is slow, but it's unsafe and should be repaired promptly.

Edit for clarification: This "leak" is internal within the master cylinder. There are no visible drips or wet spots and no loss of fluid with a worn master cylinder seal.

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  • I ordered a new master cylinder. I will update when it's installed. Commented Aug 22, 2022 at 10:01

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