Mystery brake fluid leak

[turodoggy]

Hi,

96 Legacy Outback with all wheel ABS disc brakes.

 

About one year ago, I had to change the front wheel bearings. I ended up taking the front struts off instead of just the hubs and stuff. The camber bolts were seized, even with a Propane torch and an electric impact gun. I figured anything more and I risk breaking something. This meant the front calipers had to come completely off, and all fluid was drained out of the system. At least I got a full flush on the brake fluid, with noticeable difference in braking anyway.

 

Since then I slowly lose brake fluid. Its not consistent though. I can check it after 1 week and it will still be full, sometimes I check it the next day and its half full. I can't figure out any patterns. I drive the car Monday through Friday, most Saturdays, and only some Sundays, so yeah, I can't see why I wouldn't lose anything in one week, but I can lose half the reservoir in one day sometimes.

 

Typically, leaving my driveway causes the ABS to turn on a little. Slight downhill on a gravel driveway, but never going fast or anything. Otherwise I have never gotten the ABS to turn on, well maybe one time. I drive a lot of highway, and main roads with minimal stop signs and red lights, and a little city driving. Overall not that much brake usage per trip, unless there happens to be a lot of deer out one night (yeah, some country driving).

This doesn't change for the days I lose half the reservoir either. That is what confuses me.

 

There is nothing special that causes it to lose fluid, and I almost want to rule out a brake line since it can go without losing any fluid. I've also purposely taken trips where I use the brakes harder just to see if that is the cause, and that doesn't affect it either it seems.

 

Anyone have any ideas of what to check? Sorry if I'm slow to check anything, I have a lot to do typically, and I can't always sit down to type up messages.

 

Thank you

[1 Lucky Texan]

I have read several posts of people having to replace leaking lines that run over the gas tank. I think the use the old line to pull the cupronickel (?) replacements through?

[nipper]

If you bled the system by pumping the brakes, you may have damaged tired seals in the master cylinder and are burning brake fluid. Check the line to the booster is it wet?

[turodoggy]

I have read several posts of people having to replace leaking lines that run over the gas tank. I think the use the old line to pull the cupronickel (?) replacements through?

 

Last year, when I changed the front wheel bearings, I got under the chair to check this spot since I read it was a common leak. Mine looked perfect actually. I think before I got the car, the PO got the car undercoated, so I have minimal rust under there, and this car has been in the salt belt all its life. I already planned on replacing this with the Copper-Nickle lines if it ever got rusty. More flexible, easier to work with, and won't rust sounds perfect to me.

 

 

If you bled the system by pumping the brakes, you may have damaged tired seals in the master cylinder and are burning brake fluid. Check the line to the booster is it wet?

 

I know I was careful of this when I did bleed the brakes. I just checked it, and the brake booster and line look dry, but the part of the intake manifold that the line attaches to was a little moist. I'll probably pull the master cylinder off to double check this.

 

Just the part that confuses me is in the last two weeks, I've been driving the car more, and some days using the brakes more, and I barely lost any fluid in that time, if any actually.

 

I may agree though, the brakes seem slightly weaker than they use to, so the MC may be leaking. I just had all 4 tires off to check the brakes since I am going to be replacing the rears soon, and I know there is no air in the line at this point.

[mikec03]

 

the PO got the car undercoated

The undercoating wouldn't reach the break lines which do run over the gas tank.  I've had two 90's subaru on which I had to replace the brake lines so I think that is your problem.  Incidentally, the fix is to run new brake lines from the point they exit underneath the passenger seat, around the gas tank on the right side, and connect to the break lines at the existing unions.  

[idosubaru]

brake lines above the gas tank leak due to rust.  you can't see all of the line without dropping the gas tank.  the fluid just collects up there and dries up into old caked on dirt/dust. 

 

at first it starts seeping through layers of rust.  it's not a hole, but layered rust and the fluid makes its way out and may vary based on environmental conditions. 

 

once the rust blows out - then you'll get a big leak, loose your braking, and see fluid dripping down the gas tank. 

 

i'm not sure how to test for that - but that happens often enough and i've never herad of any causes of any other "mystery" brake fluid loss that doesn't result in fluid leaks being seing. 

behind the piston boots can take on some fluid, but they dont' hold much until they leak/show. 

[CNY_Dave]

Engine running in P, lean on that brake pedal. If a line is not about to pop, you can apply all the force you can without hurting anything.

 

If the pedal sinks, it's the MC or a leaky line or wheel cylinder (if it has drum rears).

Could be a caliper leaking behind the boot, but I have never actually seen that.

 

I'd pull the MC off the booster and push it forwards just enough to check for fluid, lines still connected.

 

I don't suppose it could be the reservoir to MC seal, and it's just dripping on something hot enough all the leaked fluid is evaporating...

[Bushwick]

When you did the wheel bearings, are you positive you tightened the axle nuts to spec before inserting the cotter pin?

 

 

I couldn't get the axle nuts cracked on another car (actually bent a 1/2" breaker bar trying), and talked a shop into cracking them free, then snugging them up so I'd be able to have them removed at home. They misunderstood, and left them a little better than hand-tight. I drove roughly 2 miles like that at slow speeds, and it actually affected the front brakes and made them feel soft- all from the axle nuts being a tad loose.

 

While that really won't account for missing fluid (unless it's getting so hot it's boiling off?) it can account for a soft pedal when everything else checks out. And no, you probably won't feel anything odd in the steering, I didn't. Was one of those "you'll never believe it's possible until you experience it" situations.

[turodoggy]

Sorry for delayed response.

 

The brake line above the gas tank was good. Its possible to check without dropping the tank. I think I cheated and used my phone to take a picture of it in the spots that I couldn't reach.

 

I haven't seen any fluid at all, still.

It also isn't consistent. I went over a month recently without losing 1 drop (I always refill it to the full mark) and then in one day I lost half the reservoir.

 

The only spot I noticed moister was the brake booster vacuum hose. But I'm not sure if its brake fluid, and I tend to think its not, but I'm not 100% sure since there isn't a lot of it. I also pulled the MC off and didn't find anything between the MC and booster.

 

I've pushed on the brake pedal very hard before, and it holds.

 

My main issue is that there is these periods of time that I don't lose fluid. There was a time I had to refill the fluid a few times a week, and other times I go weeks without touching it.

 

I read something about the axle nuts not being tight enough in the service manual or something when I installed the bearings, so I know they are plenty tight. Looking it up again, if I'm correct I went to around 140 ft/lbs torque.

Now I know when I took the axle nut off, the passenger side was very easy to get off. Probably why the bearing went bad in the first place. Its why I always double and triple check everything, even if it takes longer, I know I wont have a problem.

 

Is there any other fail points besides the MC and the brake line that would be hard to notice? Its disc brake all around, and I just pulled all of them off a few weeks ago, so I would have known if any calibers were leaking.

I wouldn't think its the rubber hoses, it just wouldn't make sense how I can go a month without losing fluid them.

I'm going to try to recheck the line above the gas tank again just to make sure something didn't happen more recently and for my comfort.

I may just change the MC because I fell that is the most likely cause but its hard to prove. I also remember the brakes having more power to them. The odd thing to me is that I've never been able to lock these brakes up, or trigger the ABS, even from 50+ mph and applying max pressure I can to the peddle. The car defiantly stops quickly though.

 

If i look for a new MC, is there any that would be an upgrade for the 96 outback?

[1 Lucky Texan]

any fluid around the ABS pump?

 

does this car have a hill holder? something with that?

Edited May 19, 2016 by 1 Lucky Texan

[turodoggy]

any fluid around the ABS pump?

 

does this car have a hill holder? something with that?

 

I suspected that at one point but at the same time, I don't see enough fluid running from around the ABS pump either.

 

No hill holder. Its a automatic with 4 wheel ABS disc brakes.

[mikaleda]

Its rare, but I've seen it happen before

A bad master cylinder leaking into the vaccume booster.

 

All you need to do to verify if this is the problem would be to separate the master cylinder from the booster and look for fluid residue.

 

Edit: just read you already did that, it is possible its leaking slow enough to suck it through the vac line and burn the fluid maybe?

Edited May 21, 2016 by mikaleda

[turodoggy]

Its rare, but I've seen it happen before

A bad master cylinder leaking into the vaccume booster.

 

All you need to do to verify if this is the problem would be to separate the master cylinder from the booster and look for fluid residue.

 

Edit: just read you already did that, it is possible its leaking slow enough to suck it through the vac line and burn the fluid maybe?

 

Well I usually seem to lose half the reservoir in one trip when I do lose anything, so I wouldn't know if it is losing it slowly throughout the trip or if one event is making me lose that amount for some reason.

 

I should mention that I always seem to lose the same amount. Half the reservoir (about), and then if I don't fill it, it is just below the low fluid sensor before it causes a problem.

 

The main reason I can't rule out the MC is that if it is leaking into the booster at the beginning of my trip, by the time I stop (almost always 30 + mins driving time), the vacuum could pull up all of the fluid.

[Fairtax4me]

I suspected that at one point but at the same time, I don't see enough fluid running from around the ABS pump either.

So there is fluid around the ABS pump?