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SLOW brake fluid loss mystery


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11 replies to this topic

#1 uniberp

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Posted 10 February 2013 - 07:54 AM

Every three months the brake light on the 99 Forester comes on. Topping up the brake fluid turns it off. No leaks/ dampness underneath anywhere, no spots on the ground, brakes work fine, brake linings fine. Fluid was flushed last brake job 2 years ago.

 

Ever encounter this type of thing?



#2 Fairtax4me

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Posted 10 February 2013 - 09:59 AM

Look for any dampness around the master cylinder and booster, front and rear calipers, ABS control unit, and the hill holder if the car has it.
There could also be a leak at the proportioning valve which I think is somewhere along the rocker panel inside the car.

#3 CNY_Dave

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Posted 10 February 2013 - 11:43 AM

Probably leaking into/against the brake booster through the rod seal.



#4 grossgary

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Posted 10 February 2013 - 12:27 PM

if rust is ever an issue then they can leak above the gas tank area and not be readily detectable on the ground until it really blows good.

 

calipers/drum hardware can hold fluid if the seals brake and the rubber dust boots retain the fluid - but after months I'd assume you'd have seen some fluid by now.



#5 MilesFox

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Posted 10 February 2013 - 01:27 PM

Brake lines usually rust out at any fitting, grommet thru the body, or plactic clips that secure them to the body. Insect all these areas. Inspect where the brake lines pass thru the body under the rear seat.



#6 fishy

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Posted 10 February 2013 - 07:30 PM

Definitely check ahead of the right rear tire where the lines come out of the body and love to collect rust. I just had a fantastic brown-shorts moment last week when the lines on my Impreza blew out exactly in that location.


Since it's a fun story:
I was approaching a round-a-bout at enthusiat speeds when another car appeared from a blind entrance and was going to be in the same place as me very soon. I jabbed the whoa-peddle and POP! no brakes!

Luckily the other guy saw me coming in too hot and backed off a bit so I made that split-second call and welded my right foot to the floor and beat him through the round-a-bout. I'm sure he thought I was a collossal A-hole for cutting him off like that but he would have thought even less of me if I had parked my Impreza in the side of his Cavalier.


That's my "cool story, bro". Check for weeping rusted lines before they become a high-velocity problem.
 



#7 uniberp

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Posted 06 August 2013 - 05:56 AM

Probably leaking into/against the brake booster through the rod seal.

 

So how do I confirm this without complete disassembly? Would the booster fill with brake fluid? Could I drill a drain hole in the bottom of the atmospheric side and see if it drains? Seems like there would already be a weep hole.

 

I want to tackle this this week, I want it off the list.

 

I guess that means its the master cylinder, but I feel like I'm thowing parts at the problem, and I've never been too keen on remanufactured hydraulics.

 

Again, there are no drips, stains or softness to the pedal.  I suppose it could be that hidden over the tank line, but you'd think I'd seen a half pint on fluid leak somewhere.

 

:angry:



#8 grossgary

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Posted 06 August 2013 - 07:50 AM

So  I suppose it could be that hidden over the tank line, but you'd think I'd seen a half pint on fluid leak somewhere.

 

:angry:

friend of mine had a weak brake line i couldn't track down either.  checked it out, nothing, no wetness....she drove it around...still couldn't track the problem down.  replaced her master cylinder due to no seen fluid loss anywhere.  

 

eventually got really bad and ended up leaking enough that i saw it finally dripping down around the top of the gas tank.  pulled the rear seat and got to it through the passengers side access hole i believe.  but prior to that there was no sign of fluid.  the seats are like two bolts, really easy to get to actually, like 15 minutes to pull that plate off.

 

***doesn't sound like your issue though...you said "every three months"....that sounds really long to keep going on.  hers happened over a matter of weeks, couple months tops. like you say, seems like you'd see fluid somewhere?

 

not saying that's your issue - but MC and PB failure is so rare i'd want to diagnose it too as you said.



#9 Fairtax4me

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Posted 06 August 2013 - 09:40 AM

A slow enough leak from a caliper seal could boil away due to the heat of the brakes, before being visible or leaving a trail of fluid on the ground. I would start by pulling each caliper and checking the dust boots for fluid. Are any excessively dirty or damp looking?
Compress each piston and if the boot doesnt collapse all the way use a needle to poke a small hole in the boot. If air comes out put a little RTV over the hole and move on to the next caliper. If brake fluid comes out thats the source of your leak. Be sure to check all 4 calipers.

You don't have to disconnect any of the lines on the master cylinder just to inspect behind it. Just unbolt it from the booster and pull it out a little bit and look behind it with a flashlight. The lines are made to flex a little in that area, and there is enough flex to pull the MC out a bit.

#10 uniberp

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Posted 09 August 2013 - 10:07 AM

Look for any dampness around the master cylinder and booster, front and rear calipers, ABS control unit, and the hill holder if the car has it.
There could also be a leak at the proportioning valve which I think is somewhere along the rocker panel inside the car.

 

^Best Answer.

 

I believe I located the problem and fixed it. Very slightly loose banjo bolt on the front right caliper. It was not obviously damp, but comparison to the left side showed it was slightly darker in color with slightly more accumulated dust.

 

I realized that the fluid capillaried all over the housing, and most of it likely evaporated from the high heat generated by a caliper.

(How you like them apples... I used "capillaried" and "caliper" in the same sentence. May not be proper term.  ;) )

 

So I just tightened it a smidge, since it took only about 10 ft lbs (by feel). The hose was not damp at all, so I don't suspect the swedge. There's a copper crush washer on each side of the banjo, and I can't remember ever replacing the hose and it looks OEM. I don't wanna pull it all apart with my filthy hands and risk dirting the thing up. I sprayed it all with brake cleaner and will watch for the dampness to return.

 

Come to think of it I put KYB's on it a few years back and may have disconnected the hose at that point and replaced it as matter of course.

 

The through-body grommets are good and the lines ok. Easy to find the rear pass side one.

 

Thanks everybody.


Edited by uniberp, 09 August 2013 - 10:20 AM.


#11 Fairtax4me

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Posted 09 August 2013 - 04:42 PM

Yes, lots of heat on those capilers. I mean... Caliparries... :D


Hope that fixed it!

#12 grossgary

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Posted 10 August 2013 - 07:28 PM

now you can delay your next brake fluid bleeding. lol!






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