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Losing brake fluid without obvious leaks


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My 2002 Outback is losing brake fluid.  I keep having to top it off.  I have put in at least a pint in the last few weeks.  It seems like it pretty much happens only in colder weather (which in this context is around freezing).  I don't see any obvious leaks - no fresh spots on the ground.  On a couple of occasions I have pumped up the brakes after shutting off the engine and hours later when I got back in the pedal was still firm.  To me that makes it less likely I have a leaky line (unless the ABS keeps pressure even when a wheel line leaks in those conditions?)  I pulled off the vacuum hose on the brake booster and didn't see any sign of fluid in the hose - so it didn't seem to me like the booster was leaking into the manifold.  Any common places I should look next for this leak?

Edited by msteel
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a couple places it happens:

 

fluid is coagulating behind the piston caliper dust boots.

 

up here the rear lines that go over top the gas tank will start a very slow leak at first and you can't see it because it's just collecting/disipating on top the gas tank.  when it first starts to leak it's not so much a hole as it is soaking through, weaving it's way around layers of scaled rust before it actually exits the line - it's sort of between a leak and no leak an  may not leak unless it's under significant pressure - aka vacccum assisted brake booster, or while it doesn't seem likely - temperature/use dependent?

 

the master cylinders can leak between the master and the fire wall.  i've seen this on a 2003 OBW, but the fluid leak was obvious as it was wet.

 

they have discs all the way around.

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They have discs all around.

 

Remove the brake booster hose from the booster and stick your finger in it. If it is wet and smells like brake fluid, you have a bad Master Cylinder. This is not an unusual way for a MC to fail.

 

Thats the easiest check, after that look at all the calipers with the wheels off like Gary said.

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a couple places it happens:

 

fluid is coagulating behind the piston caliper dust boots.

 

up here the rear lines that go over top the gas tank will start a very slow leak at first and you can't see it because it's just collecting/disipating on top the gas tank.  when it first starts to leak it's not so much a hole as it is soaking through, weaving it's way around layers of scaled rust before it actually exits the line - it's sort of between a leak and no leak an  may not leak unless it's under significant pressure - aka vacccum assisted brake booster, or while it doesn't seem likely - temperature/use dependent?

 

the master cylinders can leak between the master and the fire wall.  i've seen this on a 2003 OBW, but the fluid leak was obvious as it was wet.

 

they have discs all the way around.

 

I hadn't thought of the fluid coagulating, that would explain not seeing a leak.  I guess I'll have to pull the wheels then and check that.

Even though it's a southern car now, it does have rust from its early years in New York State, so I'll have to keep that location over the gas tank in mind.  My previous Loyale had an exciting sudden brake line failure from a rusted line, and I'd rather not repeat that.

 

They have discs all around.

 

Remove the brake booster hose from the booster and stick your finger in it. If it is wet and smells like brake fluid, you have a bad Master Cylinder. This is not an unusual way for a MC to fail.

 

Thats the easiest check, after that look at all the calipers with the wheels off like Gary said.

 

There is only one vacuum hose to the booster, right?  I didn't notice any signs of wetness when I checked it.

 

I had a mysteripus brake fluid loss in a 1995 legacy outbaqck to later discover it was leaking form a plug on the bottom of the ABS module and leaking down into the framerail under the airbox

 

The ABS unit does bear some investigation.  It had a small amount of some kind of fluid, but I was thinkng it was engine oil that got there during the recent valve cover gasket job (had a misfire and found the plug seals were bad and plug wires were oily).  I'll have to clean it off and see if it returns.

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OK, well the leak is obvious now.  It is at the couplings ahead of the right rear wheel.  All four lines are pretty well rusted at the couplings, although the two that come from the front are in pretty good shape up until then.  It it reasonable to put a new flare in those lines?  Or am I faced with the joyous task of replacing the lines all the way from the proportioning valve under the hood?

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I dont even know if it is possible to replace them all the back to the ABS unit. Its been ages since I had a car do this, and never one where the body didnt match (read scrap the car). You can trace the hardlines back to someplace where it is easy to add a new fitting and line. You can also start (and in all honesty I have never had good luck with this on brake lines personally) soak the nuts with nut buster, then using a proper flaring nut tool, take it apart, inspect, clean, reassemble and see what happens. 

 

If anyone here wants to totally contradict me feel free, as I havent had to do this since I owned a 73 Super Beetle.

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http://www.nbcnews.com/business/autos/subaru-recalls-660-000-autos-brake-line-rust-n147361

The above recall affects 2005+ cars but I would certainly call SOA and cry them a river... how you've been a loyal customer blah blah blah and ask them if you should contact NHTSA on their behalf since their cars are meant to stay on the road for many years and how many other owners are unaware of this serious condition.

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nah, i just pull the rear seat bottom out (very very easy) and remove the passengers side access plate/cover.  brake lines are staring you in the face there - cut/splice/flare away there and fish the new line back. 

 

cutting and running the new line is actually really really easy.  there's not much to it. 

 

the annoying part is the flaring/joining and bleeding brakes.

Edited by grossgary
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what grossgary said - pull the back seat, cut and make your new connections where they wiill be out of the weather. Have done this on an older Suby (89 GL) cant imagine the Legacy would be all that different to do it on.

 

If at all possible, take a section of the old line, with one of the threaded fittings, with you when you go to get replacement parts, that way they can match things up at the parts store so you have the correct fittings

 

you dont have to match the bends in the hardline exactly either, get them close and make sure they wont be getting rubbed anywhere and you are good to go. If you are concerned about rubbing, put a length of rubber tubing over the line in the area you are concerned about.

Edited by heartless
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what grossgary said - pull the back seat, cut and make your new connections where they wiill be out of the weather. Have done this on an older Suby (89 GL) cant imagine the Legacy would be all that different to do it on.

 

If at all possible, take a section of the old line, with one of the threaded fittings, with you when you go to get replacement parts, that way they can match things up at the parts store so you have the correct fittings

 

you dont have to match the bends in the hardline exactly either, get them close and make sure they wont be getting rubbed anywhere and you are good to go. If you are concerned about rubbing, put a length of rubber tubing over the line in the area you are concerned about.

This is a common place to rust through the brake line

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Ok, well I finally got this thing back together. As several people suggested I put new flares into the lines under the rear seat. From there I ran a length to the factory unions and this part was pretty easy. I had bent premade lines before, but I hadn't done any double flares before so it took some practice on scrap and old lines to feel like I knew what I was doing. From there the line to the passenger side wheel was pretty straightforward. But I found the driver side line to be a royal pain as it went practically over the gas tank and had obviously been installed at the factory before the tank was put in. I finally decided on the tactic of bending the line as I fished it rather than ahead of time. This worked ok, but getting the bends right was more difficult that way.

 

Of course the rust is the reason for the line failure, but the rust also meant rusted bolts, trouble getting access panels off, broken rusted bolts, drilling and tapping out a rusty bolt, etc. I told my wife several times that when her dad offered me an amazing deal on his current Outback (which is how I got this one) that she should remind me how much I hate rusty cars.

 

I'm just glad it's back running after a week.

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