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Discussion Starter · #1 ·
My 95 900 had sat for a little over a week. I cranked the car up and eventually the idle calmed down to smooth. I applied the brakes and nothing at all. I thought maybe there's a leak somewhere, but the car still had fluid. I was able to use the e-brake to drive the car around. If you put the car in the on position but not cranked it will make a buzz sound from the engine bay under the battery. Also if you apply the brakes it will make the sound continuously. I know the abs module is behind the battery but is there something under the battery that this could be. Also could it be my NSS causing this because it is linked to my brakes upon starting the car. Once the car is running usually the noise goes away. Thanks
 

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Intrex Ed.......Also could it be my NSS causing this because it is linked to my brakes upon starting the car.

? Must be a custom job ??
Your master cylinder has leaked internally , now needs to be resealed and rebuilt.
 

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Discussion Starter · #3 ·
lol

I misunderstood the NSS system. Would it not be cheaper to just buy a used cylinder instead of rebuilding mine?
 

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Fearful it is if the prime consideration is economics re the master brake cylinder.

I do not think I would trust a used one which may have been sitting and rotting. .. ..unless it is for a very short time.
 

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There are two pistons in the master cylinder. Not a common failure. Hard to believe both piston seals would fail completely, and at the same time (!).

All I can imagine that would make any kind of buzzing sound when you apply the brakes while stopped would be the ABS, but even that seems unlikely, because it does not do anything until the car is actually moving at least 3-4 miles per hour. Noise from the ABS while the car is moving and brakes are applied is possible, because there are several solenoid controlled valves, and a small hydraulic pump operated by a DC motor, used to modulate brake fluid pressure to the wheels.

The only thing directly under the battery on the turbo is the windshield washer pump (at the washer fluid reservoir inside the wheel well). In the case of some "S" (non-turbo) models, the secondary air injection system is in the same area.
 

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Discussion Starter · #6 ·
the car has the 2.5 6 in it. The noise is definitely noticeable. You can feel it vibrate everything in the front left of the car. I'll try to get a pic or possibly a small video of the noise. The abs isn't making any noise. I'm not familiar with these cars at all and it's really frustrating lol

btw, thanks for the replies. this is helping me narrow it down.
 

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Discussion Starter · #7 ·
i'm getting ready to take out the cylinder later this week. I'm still confused on the noise it's right below the battery. You can feel it vibrate everything on that side of the car. I check gear box light has come on a few times when the car is cold. Once the car warms up it's fine. Is there a possibility that this could be part of the reason why the noise is happening??
 

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intrex_ed said:
You can feel it vibrate everything on that side of the car...
Ok, "vibrate" and "buzz", to me are two different things. I assume from the first post, you mean it does this, whether the car is moving or not. If it is coming from the ABS, then you should be able to feel it if you put your hand on it.

The Check Engine Light, that is more a function of one of the emission control systems, or engine diagnostics, but I would have an auto part store read the fault code, before anything else, that is a free service.
 

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IF the V6 uses air injection, same as the I4 w/o the turbo does; then you could be hearing the air injection pump.

If this pump is mounted using the same poor quality mounts Saab uses for the air cleaner, then probably the mounts are all broken and noises are easily transmitted...
Then, I would forget about this , turn up the music and repair the master cylinder, and do this , ASAP...I fear for the life of the ABS:cheesy:

Out of curiosity, has the brake fluid ever been renewed ??
 

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Discussion Starter · #10 ·
based on the previous owners probably not. i was going to do flush the coolant, steering, and brake this weekend, but the problem popped up before that. i apologize for the noise explanation. never heard anything like this before, and i've been around a fair share of cars, but never a saab. i just bought the car and only put a few hundred miles on it and these problems pop up.


i'm going to take it to get a engine diagnostics and then decide whether i'm going to do the repair myself or take it to a mechanic ($$$$$). btw, the check engine light hasn't come on, it's the "check gear box" which I was told is more than likely the NSS needing to be cleaned or replaced.
 

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The buzzing and/or vibration you're experiencing is the SAI pump, the secondary air injection pump which is mounted directly below the battery tray, bolted to the frame with three bolts. Its primary function is for emissions control during COLD start conditions only, and should turn off shortly after receiving a command from the ECM. The Pump will vibrate when its so to or about to give up and quit. I've already changed my SAI pump on my V6 3 times now, and each time there was a strong vibration heard coming from the front as you described. You can simply unplug the wiring connector to the pump and just disable it, it won't effect anything with performance of the engine. You may get a CEL light, but I haven't when i've disconnected mine, and mine is OBD2 while yours should still be OBD1, you shouldn't get a code.

As for the NSS, Neutral Safety Switch, yes, they periodically need cleaning, or easiest and more reliable, just replace it. Most likely cause for the Check Gear Box light.
 

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intrex_ed said:
Also if you apply the brakes it will make the sound continuously. I know the abs module is behind the battery but is there something under the battery that this could be. Also could it be my NSS causing this because it is linked to my brakes upon starting the car. Once the car is running usually the noise goes away. Thanks
The SAI system uses engine vacuum to operate, as does the power brake booster, you really should check all the vacuum lines, and more importantly, the check valve located inline the brake booster vacuum line. If a vacuum line is broken it can cause some of the problems you describe above. Maybe some of the vacuum line may be hooked up incorrectly, you need to check them. Shouldn't be related to NSS, might just be coincedence. Once the car is running and warmed up, the SAI pump will turn off, no more vibration.

Hold off on the brake master cylinder fix, you have to concentrate on the power booster and the vacuum line that supplies it first. You have to check the check valve which is moulded into the vacuum line that comes off the back of the intake manifold and goes to the power booster.
 

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Discussion Starter · #13 ·
^^ will do. thanx

btw, I'm still confused as why the noise occurs continuously while applying the brakes. i will check what you've mentioned and hopefully i can get it back on the road. i love the car overall, just frustrating when you're not used to knowing how to work on it or diagnose simple problems.
 

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There is some information missing here.

The secondary air injection system (SAI), and the SAI pump, are only used for the first few minutes of driving, until the oxygen sensor heats up enough to regulate the emissions. The air switching valve in the hose from the SAI pump to the exhaust manifold is controlled by vacuum, through a control valve at the firewall. The SAI system would not turn on and off when applying the brake while driving.

The hydraulic brake system works even when there is no vacuum to the brake servo. The brakes still work, but there is no power assist. It takes about 4x the foot pressure to exert the same force, so the brake pedal feels very firm, but even if the brake servo has no vacuum, there is no need to use the handbrake to stop.

- Vibration, buzzing, whatever you want to call it with engine running at idle, car not moving, foot off the brake, that could be one thing.

- Vibration when the brake is depressed, car moving or not, something else.

- Vibration when brake depressed and car moving, something else again...

(hope that helps to sort it out)
 

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The Yellow circled items are the SAI pump system, the red are for the brake booster, the green are check valves. Check the red areas for tightness, check the green areas for cracks, and make sure the vacuum lines are routed correctly.

Here is another shot of the SAI pump solenoid valve. The hoses are vacuum lines that operate it.



If these all check out, then move onto the ABS unit. To do this, disconnect power to the ABS unit by pulling the fuse, or disconnecting the wiring harness to the unit. Your brakes will still function as normal. If the noise still occours, then its not the ABS pump.
 

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Discussion Starter · #16 ·
lol. i'm going to try each thing that has been suggested. i'll also take a short video clip and see if this clears up any confusion on what is going on.
 
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