I all my past cars, even when the car was off, the car would stop when I pressed on the brake pedal. After a couple presses or after a couple of days, the vaccuum in the brake booster would run out, and you'd need to step on the brake pedal really firmly to slow or stop the car.

However, I was moving my '97 SE 5sp w/abs out of my garage the other day and onto the driveway. I didn't want to start the car for 5 seconds and turn it off again, so I just pushed the car out of the garage, steered it, and pressed on the brake pedal to stop the car on the driveway.

Low and behold, the brake pedal goes straight to the floor and the car starts to build speed going down the driveway heading for the street. I pump the pedal twice more and twice more, it goes to the floor. I pull the handbrake/emergency brake and the car stops just as the front wheels are entering the street.

Luckily I didn't hit anything or anybody, but in cars past, the hydraulic braking system would still work even though the power assisted system failed or was off. I thought it was a safety thing that you have a manual backup (much like steering has to work if the power assisted steering system fails, albeit with higher steering effort).

Which brings me to this... if my car dies for some odd reason as I'm coming up to a light or on the freeway, I won't won't have any braking... Has anyone else experienced this on thier cars? I don't know if this is normal on the Max's. Thanks.

-V

 

I would think if your car died for some reason while you were driving, you should still have enough pressure in the braking system to at least stop the car.

 

don't do that again

even though it should work, while the car is off you never know what's really hapenning

it's a good thing you used the e-brake

 

This is how your Maxima should work too. Even after the stored vacuum has been dissipated the brakes should work in non-assisted manner.

This is not normal. It is a defect symptom. A dangerous defect.

This is not normal. It is a defect symptom. A dangerous defect. (Repeated for emphasis.)

Your car has a defect in the brake system, and possibly more than one defect. It seems clear that your power brake booster loses vacuum instantly rather than keeping a normal reserve. This could be due to a defective brake booster unit or a defective vacuum check valve. Please refer to the Chilton repair manual (page 9-3) or the Haynes repair manual (page 9-16) for a basic power brake booster check. I don't see any mention in those books of the check valve. Identify the rubber vacuum hose which connects to the front face of the booster, Follow that vacuum hose for about six inches. There, at a junction between two lengths of rubber hose, is a plastic check valve.

The hydraulic brake system should always work. It is independent of engine power and electric power. It should work under all conditions, even if the power assist unit has failed.

This a serious and dangerous defect. Please fix this problem right away.

 

Agreeing with Daniel here. You need to go to a trusted mechanic or reputable brake shop and have your brake system inspected. Something is very wrong.

 

...for all the advice. I didn't think it should be like that. After reading these responses, I went ahead and did some more tests today in an empty parking lot/dead end street.

While driving down the street, I turned off the ignition, no radio, just to the point where the steering is unlocked. I pressed the brake pedal several times, and there was enough vacuum for several concerted stops. After the 3rd or 4th stop, the vacuum ran out and the break pedal was really heavy, but I was able to stop the car by pressing on the pedal with lots of pressure. I repeated the above twice more with the same results.

Those results conincide with what you have told me and what I thought should've happened. Which makes me wonder what happened that night that the brake pedal kept going to the floor. Hmmm.... I'll check and let you guys know if I find anything else out... That was the whole reason why I specified that I had ABS brakes, I was thinking the ABS system might've not cut out completely and was somehow dumping pressure as it does when a wheel locks up.

-V

 

Brake pedal to the floor is a symptom of low brake fluid or a faulty master cylinder. Intermittent brake pedal to the floor is an early warning of a failing master cylinder.

 

Agreed. Master cylinder looks to be the culprit. Nissan should pay for this, but I doubt it since you're probably just out of warranty......

 

Hmm...How could you tell if it's the brake booster or the master cylinder that's bad? I sort of know how a good brake booster should be like, but how do you tell if the brake booster is bad. His symptons sound like a brake booster problem.

This is when a brake booster is good.

1. With the car off, press and hold the brake peddal.
2. Start the car and the brake peddal should go down very slightly.
3. Still hold the brake peddal and turn off the car. The peddal should raise slowly.

If the Master cylinder is bad, you would have no or little brake pressure regardless the car being on or off.

His problem only happens when the car is off and leads me to believe it's the brake booster.

Any other thoughts?

 

Brake pedal to the floor, like Daniel B said, is absolutely not normal. Even without residual pressure (which lasts like one stop then that's it), the brake pedal should provide some resistance to give you the feel of pressure (and hence stopping). I have found, however, that in my Maxima I have to literally stand on the brakes to stop the car when the pressure is gone. I have tried this test in other cars and I didn't have to press as hard as I do in my car. And it's not like I can't press hard either, I'm 6'2" 190lbs, and had to literally press so hard that I lifted myself off my seat!

 

bill99gxe---> I'd check to see if it was under warranty (time wise), but I don't think the 132,000 miles on the car would look good to the dealer

I took a look at the master cylinder, and the fluid level is ok and there don't seem to be any leaks between the cylinder and the booster which seems to be a common area for leakage. I've done followup tests afterwards, and it seems like the residual vacuum pressure in the car will stop the car easily for the next 2-4 stops with the ignition off. In those residual tests, after boost vacuum ran out, the car would stop, albiet with LOTS of pedal pressure. The pedal was rock hard, and since I only weigh like 135lbs as compared to Eric L , it took a herculean effort to get the car to slow/stop.

Since my master cylinder appears fine and the car stops ok now, should I still worry? Or could what happened the other day been some fluke with the ABS modulator somehow being stuck in the pressure dump mode as the car was being turned off when I parked it causing the brake pedal to go straight to the floor? Thanks.

-V

 

Originally posted by vmok


hehe.....SMALL step-out on my part. I figured a 97 would have no more than 70k...... Not that Nissan would really care if you had only 100 miles on it anyway.....



I would.



Good possibility of an ABS related problem....didn't consider that originally......with the seemingly inconsistent behavior and my experience of a similar occurence with my dad's old 89 Max (which I believe the 3rd and 4th gens share master cylinders) that required a master cylinder replacement, I assumed master cylinder. I'm not versed in ABS equipment failures and their effects so I won't speculate. Find a REAL good brake shop and let them have a crack at it......