[dogsdangles]

2003 SAAB 9-5 Aero wagon here. Brake system has TCS/ECS

So I just replaced my brake booster/servo and all vacuum lines - including the hard plastic line/assembly with the check valves between the brake booster, throttle body, and vacuum pump - and now I have no power brakes! There's no air in the lines; the brake system has been properly bled per the WIS procedure, and there's no play or sponginess in the brake pedal. I'm simply not getting any power assist whatsoever while braking.

Any suggestions on what I should to do troubleshoot this issue? I don't think I quite know how to properly "listen" to the brake booster to diagnose it (indeed, the reason I replaced the brake booster was because my mechanic diagnosed it for me, and then I opted to do the work myself without confirming his diagnosis).

Thanks!

 

[Mimmi]

Did you started engine? Vacuum pump is mechanical.

 

[dogsdangles]

Did you started engine? Vacuum pump is mechanical.

Yep. Engine on.

 

[thaistatos]

do you have vacuum at the vacuum pump.
push the red part down, remove the tube, remove the red part, put your finger on it.

check both check valves of the new tubing.

 

[dogsdangles]

do you have vacuum at the vacuum pump.
push the red part down, remove the tube, remove the red part, put your finger on it.

check both check valves of the new tubing.

Hey, good suggestion!

I checked the vacuum at the vacuum pump, and I do draw a vacuum. The negative pressure is only so much that I can place my finger over the pump inlet, and easily remove it (I tried with a piece of paper first to be safe!). How much vacuum is this pump supposed to draw? Just as a guess, I'd say right now it's somewhere around 10 psi (~ 700 mbar) or less. Is that sufficient for brake boost?

So with that, I guess I get a bit of brake boost when I brake, but if I need to come to a stop quickly - if I really slam down the brake pedal - the effect leaves much to be desired.

Thanks again for the suggestions!

 

[thaistatos]

Did you removed the red part before testing? Otherwise it will not seal when you put your finger on it.

Vacuum pump, mechanically driven – 9-5 2002 | SAAB Workshop Information System Online

according to technical data:
Max. negative pressure bar 0.95
--> -0.95 bar --> total pressure 0.05 bar

I don´t now how you guesstimate your pressure level, total pressure or vacuum (0.7bar total or -0.7bar vacuum)?

I have no experience if these types of pump have any wear? They are running completly in engine oil.

Other dirty check: remove the tube, suck on it with your mouth, press your tongue against the tube and check, if the brake booster holds the vacuum (take care that nobody is watching you during the test ;-) ). repeat with second

The O rings inside the fitting (below the red part) will get hard over time and might not seal, therefore no vacuum to the brakebooster.
Metric o ring would be 8 x 2.5 mm, maybe you find something imperial.
Be careful if you remove the old ones, they tend to brake apart and fall into the intake manifold or the vacuum pump. vacuum cleaner might be useful.

Vacuum pump is not the main source of vacuum, it should only support in certain driving conditions.
Is it hard or easy to press the brake when the engine is running? To compare, press brake pedal several times without engine running, brake pedal should get very hard to press. If you start the engine, brake pedal (immediatly) should become softer and much easier to press down.