This just started tonight - twice when I applied my brakes it felt like I was braking with no power assist like when the car is off. The car still stopped but it took a lot longer to stop than it should have. What's even more strange is that while this was happening the engine would race to about 2K RPM's until I came to a complete stop. This only happened twice and I was out for a couple of hours and used the brakes many times with no problems. Does anyone have any idea what could be causing this? I'm afraid to drive the car now because I don't want to get into an accident if I have to brake quickly and the car doesn't stop. I drove up and down my steet when I got home trying to duplicate it with not luck.

 

Check the vacuum line from the manifold to the brake booster. The brake booster is the big black round thing on the drivers side firewall. The vacuum line runs out of the booster to the intake manifold on the passenger side. It's rubber but has a section of metal pipe in the middle.

A leak in the line would cause the power assist to stop assisting and could also cause a change in the RPM.

Jiggle the hose at different places and listen for a change in RPM or a sound like air sucking. Especialy look at the ends near the clamps. That's where hoses usualy fail. If you find a damaged section of hose then it's an easy fix. Just make sure you use vacuum line to replace the section.

Let us know what happens.

 

I'm not sure if this is the same problem I had last year because I never had rpm issues.. but on cold mornings last winter, mine would do something like that. I would press on the gas, and the pedal would go down and pretty much get stuck, but not brake hardly at all. After a few minutes it would release and brake like normal. Like I said, it only did it several times, and ONLY on really cold mornings. We ended up replacing one of the vacuum lines that led to the break booster, and it's never done it since. I really can't remember which hose it was... but it's one that has a check valve in it. Hope this helps.

 

Did you check the brake fluid level in the reservoir? Every time you stop it leans forward and if the fluid is too low, air could get in the lines. Also if the brake master cylinder is getting bad it could be loosing presure.

 

Bah... your answer is better than mine lol

 

That was the first thing I checked but it was right at the full line. I was hoping that's what it would be.


I will check that first thing tomorrow morning. That's a really good suggestion. I'll let you guys know how I make out.

 

I just went out and started the car and checked the vacuum line. Everything seems to be tight from the brake booster to the manifold. I wiggled it in several different places and didn't hear the rpms go up. Any other suggestions? I can't really take it to Nissan or my mechanic because it happens infrequently and I'm having a difficult time duplicating the problem.

 

Well, like Derrick2k2SE said... there is a metal piece inside the rubber hose that is a check valve... when this was happening to me, my dad thought that maybe there was water or moisture inside that was freezing, not letting anything through the hose. I replaced mine because it wasn't that expensive anyways... since my dad is a mechanic at the dealership
Mine hasn't had that problem since last year when I replaced it.

 

I can try that but did you replace the whole thing from the brake booster all the way to the manifold?

 

I would also check for vacuum leaks all around the manifold. The rising RPM can be a sign of a vacuum leak. I guess a large leak could cause the booster to loose vacuum as well. I really don't know.

Are you sure you didn't have your foot on the gas and brake at the same time?

 

Just the hose with the check valve

 

The first time it happened I thought for sure that must have been it but when it happened again I knew there was something else wrong. I went out in the car today and it did it once. It seems to happen only when I'm braking somewhat hard to come to a quick stop.