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Discussion Starter #1
Have had rear brakes replaced, lines flushed, abs module repaired, and hard vac lines to brake booster replaced.What are the possibilities? I need to replace my front brakes but I cant see that making the pedal itself feel stiff, thoughts?

I've also been replacing all my vacuum lines but still suspect a vac leak. Replacing coolant bypass valve in literally a hour or two, could it possibly be making a big enough vac leak to cause the brakes to feel stiff? Previous mechanics confirmed all my brake lines are solid but I need to double check that too (can't really trust any mechanics around here to give you the full truth.)
 

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How old is the car? Have flexible rubber hoses been changed? I have experienced them when they decay inside the rubber swells and closes off the flow of fluid.
Just a wild shot in the dark if your vacuum lines and booster are OK.
Bill
 

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Discussion Starter #3
car is a 2000 so about 20 years old. To my knowledge they have not been changed, I'll have to look into that.
 

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Interesting comment about the rubber lines restricting flow. I have never found that to be the case but I guess it's possible, typically when the rubber lines are getting old they will flex too much under pressure and give the brake a soft feel. I roadrace motorcycles and can attest to there being a significant feel change when going from standard rubber to steel braided (stiffer) lines. Unless it takes a very high amount of pressure I think what you're feeling may not be abnormal - for what it's worth I thought the same thing about my 06 at first but got used to it quickly. Let us know what you find.
 

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I had a car on which I thought a caliper was frozen. It took effort to get braking action, and then the brake would drag. It was the flexible hose. The inside has closed right up.
But, do you have a frozen caliper, blankcortex?
You said you changed the brakes.
 

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The 9-5s can have a pretty stiff brake pedal, compared to say an NG9-3. On my car, more braking means pressing harder, not pushing pedal further in. (At least mostly pushing harder.)

You can try working the pedal with the engine off, and then start the engine. If there's a noticeable difference, then the vacuum assist is working fine.

Also, you can try rolling gently forward with the engine off (and nothing near you) and see if the car can be stopped with the vacuum assist all used up. If it's still possible to stop the car without going to max leg effort, the brakes are probably okay.
 

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more braking means pressing harder, not pushing pedal further in.
I agree with this, it has to do with the hydraulic ratio of slave cylinders to master being low. I don't know what the piston sizes are for each caliper on these cars but you'd calculate the ratio of (total caliper piston area)/(master cylinder area). I can tell you on sport bikes a change between a master of 16mm to 19mm keeping the same calipers is a massive difference, dropping hydraulic ratio down to less than 20:1 gives a very hard lever feel with almost no travel, very good for modulation because you just modulate pressure not position. My point is that I always just thought the hydraulic ratio was low on these cars, inherent to the particular parts they're set up with. Maybe someone can chime in with some piston diameters, it would be interesting to know the ratio to compare now that I'm thinking about it.

If yours is really bad maybe you do have an issue, but if you need to do them anyway I'd replace the pads in front first, the majority of the braking power comes from the front and if your pads suck your pads suck.
 

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Is your car an automatic with a vacuum pump? The vacuum pump can developer a “leak” where it sucks in engine oil which then works it’s way into the booster, filling the brake booster. That will give you a hard pedal and eventually lead to brakes dragging because the calipers can’t retract.
 

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Discussion Starter #11
So at this point only the rear brake pad and rotors have been replaced. Calipers on the rears were operating normally. The mechanics didn't say anything about my rubber lines but I wouldn't expect them to go out of their way to say anything.

The front brakes I suspect the passenger side caliper is sticking infrequently, I experience steering drag to the right occasionally, its more pronounced when using the brakes. I've also noticed my passenger side rim looks blackened with metal dust that none of the other rims have. Is this indication of a sticking caliper?


I'm still planning the front brake job but I'm planning to do both calipers as well as pads and rotors. I'm still ruling out all vacuum leaks and caliper performance before thinking about the brake booster being done for.
 

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Discussion Starter #13
Successfully replaced coolant bypass valve. Already noticing my heater is working immediately instead of taking a long time like usual. I will do a test drive later and report back if the fixed vacuum leak was the cause.
 

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Discussion Starter #14
Also I can say from previous experience that without the engine on, its nearly impossible to fully stop the car (max leg power).
 

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How much DIY are you willing to undertake? And have the brakes always been like this since you owned the car?

If it were my car (I once owned a 1999 9-5 2.3t), I would visually check the hard brake vacuum hose that you had replaced. Then I would CAREFULLY use a plastic pry tool or forked interior fastener removal tool and slowly lever the hard plastic line connector out of the brake booster. Doing this with the car cold and sitting a while, it should give a "whoosh" as the connector pops out of the grommet - that's the vacuum in the booster being released. If you have a leak, there will be little or no vacuum to release, and not much sound.

Since you indicate that braking response really hasn't changed much, there may be nothing really wrong with the braking system - but your front pads could be an issue. The fronts do the majority of the braking, and 9-5's were designed with a boost/assist level appropriate for semi-metallic pads. A number of owners on this and other boards have complained that ceramic pads don't give them enough "bite" for their liking, and that this is more noticeable in cold/wet conditions. You might want to search 'brake pads' and owner opinions before you replace those front pads.

Hope this helps.
 
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