Brake booster leak

[Souperoo]

My 2004 Forester started loosing the vacuum in the canister after sitting overnight.  Press on the brake before starting and it would be rock hard, start it and it works.  I first suspected the check valve in the hose but that didn't cure it.  It kept getting worse, to the point that it would loose vacuum in 10 minutes.  It also started running a little odd and I was thinking the vacuum leak was the problem.

 

I just changed the vacuum booster and I am hoping that was the problem.  On the test ride it did seem to run a little better.  The brakes work great.  But a question.  After turning off the engine, how many pumps of the brake pedal do you get before it runs out of vacuum?  I'm only getting 1.5.  Is that normal?  I'll know in the AM if it held the vacuum overnight, I hope so because it was a real PITA to change.  Worst part was working under the dash, that isn't exactly comfortable.  I know I should have posted here BEFORE buying/installing the booster but didn't think it could be anything else.

[1 Lucky Texan]

not sure what's normal, have read often that it is "1 or 2 stops" so, maybe you're on target?

 

If you still have a concern, perhaps you could compare vacuum gauge readings; examine hooked up normally, then compare to a reading with the brake booster hose pulled and its port plugged?

[Souperoo]

Hmm, the pedal only went half way down this morning, so it only had a little vacuum left.  It does however seem to be easier to pull out in 1st (standard shift) then it was before so maybe the old one did have a significant vacuum leak.  Changing the booster included disconnecting the brake lines from the master cylinder which meant bleeding the brakes, and I like to go overboard and flush the system (used a quart of fluid).  In the front the old fluid was really dark on both sides, so at least that has fresh fluid again.  For whatever reason, the rears came out clean from the start.  All but one bleeder required a map torch till they were red then quenched with a wet rag (rinse and repeat) twice to break them free.  Pretty easy to bleed them by yourself.  Put a hose over the bleeder and into a can and pump away keeping the master full of course.

 

Oh, my A/C took refrigerant when I first got the car.  Underneath the booster and master cylinder is an a/c line with a joint.  It had some oil around it so I tightened it up and was surprised at how loose it was.  Hopefully that was the only leak.  I sure am hoping I run out of problems soon.

[Gloyale]

My 2004 Forester started loosing the vacuum in the canister after sitting overnight.  Press on the brake before starting and it would be rock hard, start it and it works.  

 

 

this is normal.  

 

I don't think you really had an issue.

 

Placebo affect of having done something is making it seem better.

[Souperoo]

this is normal.  

 

I don't think you really had an issue.

 

Placebo affect of having done something is making it seem better.

All I know is that the first couple weeks I owned it, it didn't do that.  Then it started to do it overnight, rock hard in the AM.  Then after 10 minutes.  Now it takes overnight and I got 1/2 pedal worth of vacuum.  That's a big difference, not the placebo effect.  Now thinking it runs better without the vacuum leak, that could be the placebo effect.  (however it does run smoother after I wash it   )

[1 Lucky Texan]

system is supposed to give you a coupla stops after an engine stall while driving. I doubt the system is intended to retain a full vacuum overnight (Perhaps a new car CAN, and an older car can't - but it really doesn't NEED to.)  as, before driving in the morning vacuum will be re-established quickly after starting the engine.

 

BUT, bleeding brakes with full brake pedal travel has occasionally been reported to compromise master cylinder seals.... dunno if that could match the symptom you have or if you bled the brakes that way......?

 

 

do you still have the old booster? maybe a test for it could be rigged-up?

Edited May 30, 2018 by 1 Lucky Texan

[Souperoo]

Like I said, the old one started loosing the vacuum in 10 minutes.  Also I've had many high mileage cars that did indeed hold the vacuum overnight,  I've never had a car that didn't.  If not for that, I never would have suspected it was going bad.  There are only 3 things that can cause the problem.  The check valve inside the vacuum hose, the hose itself, or the booster.  I'll ask my mechanic friend if the vacuum leaking down in 10 minutes is normal on some cars.  Since the new hose with the check valve didn't fix it, I saved the old one.  So just for curiosity's sake, I'll swap it with the new one, that's easy enough.

 

No, a bad master cylinder would act completely different.

 

The proper way to test it would have been to use a vacuum pump with a gauge.  Simply pump and pull a vacuum, hold it, and watch the gauge to see if it leaks.  But I don't have a vacuum pump.  The old booster is boxed up to be shipped for a core credit.

[1 Lucky Texan]

it may take a lot of pumping but, aren't there hand-operated vacuum pumps? maybe loaned-out by parts stores. usually used for brake bleeding.

 

 

 

www.youtube.com/watch?v=h0Z4WPqhLqc

Edited May 30, 2018 by 1 Lucky Texan

[forester2002s]

My 2002 MT Forester has never held brake vacuum for very long after the engine is shut off.

I've always considered it normal (I bought the car new).

 

The driveway in front of my garage has a slight downward slope.

So, when I activate the remote to open the garage door, I turn off the ignition and put the car in Neutral.

As I coast slowly into the garage, I can feel the vacuum dying.

By the time that the car comes to rest, there's no brake-assist left.

 

Why do I do this?

Mainly so I don't introduce too many exhaust-fumes into the garage.

 

But it also reminds me of the fictional character 'Garp' in the novel (+1982 movie) 'The World according to Garp'.

Garp (played by Robin Williams) rolls his car like this into his garage, mainly to amuse his kids.

But one day there were unexpected consequences!  You'll have to read the book, or see the movie, to find out what happened.

[Souperoo]

Hmm, I saw the movie but don't recall that scene.  In fact all I can picture from that movie is that beautiful house he lived in.