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Brake pedal sinks to the floor,


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#1 Hank Roberts

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Posted 12 July 2005 - 05:21 PM

again .... 1988 GL 4wd SPFI.

Brakes have been done, and bled.
And went flat, and bled.
And went flat, and bled.
And they found an internal leak in the master cylinder and replaced it.
And they went flat again.
And they bled them and found more bubbles but no leak anywhere.
And they went flat again.

The mechanic is, unfortunately, apparently a theorist. He's done Subarus for so long he knows exactly what could be wrong.

And he says he can't see any sign of a leak.

So it has to be the new master cylinder they put in is bad.

Well, I figure -- these old vehicles may be inventing new ways to go wrong, that the expertise of the mechanic is blinding him to.

I asked him to promise swear to God cross your heart hope to die if I catch you lying, to have his youngest assistant with the best eyes look very carefully along all the lines for any sign of a little leak.

I can _imagine_ that there's a crack somewhere that is letting a bit of air into the system but not making a big puddle of fluid.

Anyone with experience got any other ideas where to look?

This has been the car from hell, now -- three months and still in and out of the mechanic's -- first Subaru I've owned.

#2 grossgary

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Posted 12 July 2005 - 06:20 PM

sounds like a master cylinder. if the master cyilnder went bad while installing new brakes, then it wasn't done correctly most likely. the cap was probably left on the master cylidner while at least one piston was pushed in, that will ruin the master cylinder seals. if that were the case then the mechanic, not the car is to blame for that failure. now..on to your problem....

based on the pedal going to the floor i would suspect or at least want to start looking at something between the brake pedal and master cylinder. check to make sure that when you push the pedal the master cylinder is indeed doing something. will the fluid bleed out okay? in other words it is actually under pressure when the pedal is pushed? that will verify the pedal linkage and booster are doing their thing.

was the new master cylinder properly installed and bled before anything else? there are directions tpyically with the new part on how to prime the master cylinder and get all the air out of it.

if that was replaced then i'd possibly suspect the brake calipers. the calipers have an oring around the piston that can leak and then once past the oring the fluid could be partially or completely contained by the rubber dust shield around the piston as well. that is where i would suspect a minor leak that isn't detectable. caliper rebuild kits are inexpensive...a few dollars typically.

was it bled correctly, i'm guessing so, sounds like you're tried alot.
make sure all the pads were installed! forgetting one, the caliper piston could get pushed out of it's cylinder.

another test would be to attach some clear hose to each bleeder screw at each caliper (one at a time). make a loop in it so no air can get back into the caliper. the fish air-line hose at wal-mart works okay, i have some that i use for bleeding. this will allow you to bleed without getting air in the lines AND you'll be able to see your fluid. if one particular line is indeed causing the problems then you should see large amounts of airbubbles in whatever lines is causing the problems....right, left, rear, front caliper line. this will narrow down where your bubbles are coming from if that's the case.

#3 EYE_WHY

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Posted 12 July 2005 - 09:29 PM

I (think) I have the same problem (?) My brake pedal goes a good ways down to the floor without doing any stopping at all. Infact, the other day I had to stop quickly from about 55mph. I jammed the brake pedal to the floor (and I mean the floor, as in I was pressing it all the way in) and I didn't slow down as fast as I would have liked to, I was scared to the point of thinking about yanking up on the e-brake but before I could, traffic started moving again. Still, the experience left me a little weary of the braking power of my 94' loyale. Any ideas?

#4 busdriver

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Posted 12 July 2005 - 10:00 PM

I've been having a problem losing fluid and poor braking as well, until I realized the rubber gasket has to be just perfect on the m.c. for it to seal correctly. it wasn't letting the system pressurize (if you will) and let fluid leak out. Just my two cents.

#5 aba4430

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Posted 13 July 2005 - 05:53 AM

The pedal on my 87 Brat was not very firm for years. Just last month, I replaced the rotors and pads (front) and this time we left the hand brake released when bleeding. This has made a huge difference to the pedal feel. It is rock solid and firm now. Just a thought, unless you find something mechanically messed up. In any case, if you manually bleed your brakes, try doing it without the hand brake applied.

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#6 Bill90Loyale

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Posted 13 July 2005 - 02:09 PM

My brakes blew out about a month ago. Turned out that the little hangers for the metal brake lines to the rear brakes allow corrosion to attack the small diameter metal brake line right where the hanger is - which finally springs a slow (or in my case) massive leak. Replaced rear lines. Brakes are fine.

#7 MorganM

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Posted 13 July 2005 - 03:52 PM

Ensure you are bleeding brakes in crossdirectional patern; rear right, front left, rear left, front right. Also ensure that the new master clyinder was 'bench bleed'. Once the MC is bench bleed then you bleed the rest of the lines.

I use speed bleeders; the true 'one man bleed kit'. http://www.ultimates...t=speed bleeder

Pump the pedal and hold it tight; with the engine off. If it slowly sinks to the floor then you have a leak somewhere. If it holds tight but isnt giving proper braking power then you simply have air in the lines. Leaks are easy to find; look for the wet spots!

#8 Sweet82

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Posted 13 July 2005 - 04:52 PM

I (think) I have the same problem (?) My brake pedal goes a good ways down to the floor without doing any stopping at all. Infact, the other day I had to stop quickly from about 55mph. I jammed the brake pedal to the floor (and I mean the floor, as in I was pressing it all the way in) and I didn't slow down as fast as I would have liked to, I was scared to the point of thinking about yanking up on the e-brake but before I could, traffic started moving again. Still, the experience left me a little weary of the braking power of my 94' loyale. Any ideas?


Pump your brakes, don't just hold them to the floor. If they come back alive you should consider bleading them and then start looking at the mastercylinder. I'd bet you have a mastercylinder problem too. :eek:

It's not a big deal to replace. Lots of good info in this thread.

Good Luck,
Glenn
82 SubaruHummer
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#9 Syrinx

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Posted 13 July 2005 - 09:20 PM

I have found sometimes that after doing the brakes, bled good and tight then driving, the brakes go soft again and require re-bleeding. Somehow I never got all the air out in the first place.

I addition, the hilholder is a prime place for air (vacuum) leakage/suction. This has beena repetative problem for me over the years.

From what youv'e said it sounds like a mechanic problem. The brake system is one of the most simple closed loop systems around and doesn't have many failure points.....

Soft brakes mean only two things: bad seals or a leak. That's it. no mystery there.

#10 Hank Roberts

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Posted 13 July 2005 - 10:36 PM

... the hilholder is a prime place for air (vacuum) leakage/suction. This has beena repetative problem for me over the years.

From what youv'e said it sounds like a mechanic problem. .


Hillholder -- now this car also has its fourth and I hope finally correct replacement used transmission, not yet tested by me (the brakes went flat the most recent time when I went to drive it away from the mechanic with the 'new used Japanese' transmission in it).

How's the "hill holder" connected up to the transmission and brakes? What could they have forgotten to do, or done wrong?

As to leaks -- the mechanic's proclaimed there's no way there could be a leak that didn't make a big puddle. I tend to believe the posting earlier that it's possible an O-ring is leaking inside a dust cap and letting air in, rather than a lot of fluid out, and making a hard to see or hidden wet spot.

I'm going to present THAT printout to the mechanic tomorrow and see if he says he knew it all along but was sure it couldn't be happening - his usual answer when I show him suggestions made online here (sigh).

And he hasn't yet seen the eye doctor to replace his "dime store reading glasses that he's been blaming for trouble seeing things. I get, kinda, frustrated .... but he promised to have a young coworker with good eyes look for leaks, so, I'm hoping for better news tomorrow.

Hill holder? First I"ve heard of that possibly being involved. Say more?

#11 MorganM

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Posted 13 July 2005 - 11:31 PM

It's not a one way system. ANY leak (O ring or whatever) is going to push out fluid when you hit the pedal and suck in air when you let off. Eventually, no matter how small the leak, you will have a puddle on the ground.

Since you arent actually working on it yourself then you are at the mercy of whoever is working on it; I really doubt he's gonna stand there and debate with you what you 'read on the internet' (mechanics LOVE that!) vs what he thinks needs to be done. If you do not think this service station is giving you comprehensive service it's time to take it elsewhere or take matters into your own hands and do the suggested things mentoned in this thread.

Good luck and use the e-brake if you take it to another shop! :drunk:

#12 NorthWet

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Posted 14 July 2005 - 12:00 AM

The hillholder has 2 brake lines running to it: One front brake, one rear brake, diagonally located from each other (I can't remember exactly which). It has a valve in it that either lets pressure pass through it or holds the pressure until the valve is deactivated.

The valve is activated by both vehicle inclination (has to be nose-up a certain number of degrees) and cable movement from a cable connected to the clutch release fork.

A little story: 82 wagon, brake pedal went to the floor, no obvious sign of a leak. Bled the system, no change. Changed the master cylinder with a believed-good used unit, still the pedal went to the floor. Got distracted for a week, came back to bleed the master and brakes more thoroughly, and found the brake pedal rock hard (in a good brake sort of way). I do not know what happened. Maybe a dry seal swelled to usable again, maybe an air bubble worked its way out. I do not know.

Simple brake systems sometimes act strange.

#13 fiater

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Posted 14 July 2005 - 01:02 AM

This reminds me...

Pedal was always lowish on my 86 Brat. Stopped OK, and pedal never sank lower with constant pressure, just engaged lower than I'd like. I noticed when I adjusted the hill holder to the clutch release point that when the hillholder was engaged, the pedal would be perfect, and start pressurizing within the first 1/4 inch or so. Once the hill holder disengaged, the pedal returned to its lower engagment point. I figure maybe it's some bit of reserve space to ensure the hill holder wont get stuck on? Replaced the MC twice, still have same prob. I just live with it now. BTW, if I pump the brakes on a stop, it seems to bring the pedal up to where it should be. No leaks, and brakes evenly. Just my thoughts.

Carl
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#14 EYE_WHY

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Posted 14 July 2005 - 11:47 AM

I haven't noticed any puddles from brake fluid and with the car off, the brake pedal is hard as a rock. I really want to get this fixed, it makes me nervous to think that I may not be able to stop in time if something happens in front of me.

#15 Sweet82

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Posted 14 July 2005 - 12:04 PM

I haven't noticed any puddles from brake fluid and with the car off, the brake pedal is hard as a rock. I really want to get this fixed, it makes me nervous to think that I may not be able to stop in time if something happens in front of me.


Your problem is not going to cause puddles of fluid to pile up on the floor. Your system needs bleeding or your master cylinder needs replacing!

Pump your brakes when you need to stop!
Bleed your brakes as soon as you have time.
If this does not cure the problem.
Replace your mastercylinder!---then you need to bleed the system again :lol:

Quit worrrying and do this!

#16 NorthWet

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Posted 14 July 2005 - 12:49 PM

... Replace your mastercylinder!---then you need to bleed the system again :lol:

Quit worrrying and do this!

"Replace your mastercylinder"... yet again. Sounds like easy advice as long as you are not the one who has been frustrated for a month just trying to get your car running, and having a succession of improper or non-working parts installed. If I were this guy I would be pretty near the end of wanting to deal with these problems.

In my 35 years of working on cars, I have never had a master cylinder, either new/rebuilt or one that I have rebuilt myself, fail to work after I have installed it. (Well, until recently.) I have never had to bleed the master cylinder, and wheel bleeding has never failed to give good results (I have probably been lucky on this score). I imagine that most peoples' experience with brakes are similar: You get the parts replaced and they work.

So, after spending $100+ for a master, plus paying the mechanic to install it, I wouldn't think that the best advice that we could give him is to put on another master... at yet another $100+ plus labor.

I am not trying to upset anyone :) , but Mr. Roberts seemed frustrated in his "transmission" thread, well before this brake problem reared its ugly head. I know it can be hard to diagnose from a distance (my last post showed that I couldn't do it with my hands on), but hopefully we can help Mr. Roberts before he decides that the best fix involves a gallon of gas and a match. :rolleyes:

#17 Hank Roberts

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Posted 16 July 2005 - 05:18 PM

>gallon of gas and a match
Yeah, I listen to Car Talk myself.

Well, I just went to pick up the car.

Only the front office/bookkeeper was there to give it to me.

It's exactly the same. I got flat denial from her, she said her Subaru brakes (an automatic) are exactly the same.

It's like this.

Engine off, pedal is firm and high.

Turn the engine on, the pedal starts to sink, and in about three or four seconds is way down below the gas pedal reaching a firm stop just half an inch or so above the depressed clutch pedal.

It comes up when I pump it, and goes down again when I hold it down firmly.

When I drive it, it's firm at each stoplight or stopsign, at first. If I'm on a slope, the pedal slowly sinks down over a few seconds. If I lift up my foot and press down again it's still very mushy and low, and pumps up in three or four presses-and-releases.

This does not feel right. This does not feel like it did for a few hundred miles, a couple of times, in between the several times this has been bled, and the two times the master cylinder has been replaced now.

They told me yesterday (when they called me too late to pick it up while the mechanic was there and said I could get it from the bookkeeper today) that this last round had been a defective master cylinder, the new one they put in last week was bad.

Each time this has taken a few days and a few drives.

Now -- as long as I am very light on the pedal the car will stop fine, with the pedal fairly high.

If I don't PRESS DOWN on the brake pedal, am real light on it, it stays held properly.

The pedal only goes down if I stand on it a bit -- as I would on a 4wd road, or sudden stop, or on a steep hill.

So -- give me a sanity check. I never owned a Subaru before this one. It's been about 1000 miles in 3 months, been in the shop over and over for this problem, and others.

Am I missing something here? As far as I'm aware, once the vehicle is halted by the brakes, there should be nothing left to compress -- the pedal should have maybe a slight bounce to it but not any further motion down to the floor.

I am supposed to now take the vehicle out for 500 miles and really test this fourth attempt at replacing the transmission -- which means going up onto the forest service roads.

Do I have anything to worry about with this brake pedal behaving as it is? It scares the hell out of me to imagine a bad situation on those roads and these brakes. But the woman today tells me hers are just the same on her GL (automatic).

Of course she also says they never hold the brake pedal before starting the engine -- hers is an automatic, but she refused to do that, so didn't feel it suddenly lose pressure and sink as soon as the engine started. Not the little 'step down slightly' of the vacuum assist, but like it starts to leak or get bubbly as soon as the engine turns on.

Right now, I believe I have to take it back in Monday. But when I do the work order --filled out by the woman who just tested it, the front office/bookkeeper -- is going to say "customer claims pedal sinks to the floor but I could not make it happen."

Each of these go-rounds makes me late to work, too. So it's not going to be fun.

Is there any way what I'm describing can be normal on the Subaru?

#18 Hank Roberts

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Posted 17 July 2005 - 01:19 AM

>gallon of gas and a match
Yeah, I listen to Car Talk myself....

Is there any way what I'm describing can be normal on the Subaru?


NOTE there are two different people describing the same problem in this thread, me and Eye Wh.

NOTE, while it's been three months and three master cylinder replacements and seven or eight bleed and fluid replacements for me, I'm not being charged for these -- the shop in Berkeley charged me once, the first time, for finding the problem -- and is still trying to find the problem.

I can't do this myself -- my hands don't work. Carpal tunnel, failed surgery. So I keep trying to figure out what's going on.

A few more hours of searching, and I find over and over, for all kinds of cars and years, that "pedal sinking to the floor while at a stopsign" is always described as indicating a master cylinder failure.

I can imagine three bad ones in a row. Heck, I've seen so much manufactured junk for sale the last decade that I am never surprised when the first three or four of anything I buy come out of the box as crap.

So I guess I just go back to the mechanic on Monday and say try again.

#19 NorthWet

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Posted 17 July 2005 - 09:41 AM

I am in a little bit of a hurry so don't want to look back for some info but want to throw something out before I forget it totally:

Are you losing fluid? One possibility based on high-and-firm pedal while engine off but sinking pedal when power-booster is working is that the power brake booster diaphram has a tear/rupture, allowing engine vacuum to be applied to the master cylinder seal and sucking fluid into the power-booster.

The booster may have a vent that prevents this, though. Even if this is the case, perhaps a leaking power-booster might give you your sinking pedal feeling... I will have to think about that.

#20 Hank Roberts

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Posted 17 July 2005 - 10:37 AM

Mine is not losing fluid -- no wet spots according to the mechanic, and no sign of low level in the reservoir.

Eye also said his is not losing fluid.

#21 Hank Roberts

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Posted 17 July 2005 - 10:49 AM

Could the booster diaphragm 'balloon' without actually leaking? So when the engine is running, it makes the total space available for brake fluid larger?

Old machinery discovers new and unexpected ways to fail. I know that.

Mechanics who are sure they know it all are most likely to be surprised by new failure modes that develop when materials start to degrade -- or new parts are made with new failure modes out of the old spec.

In other words , help!

#22 heartless

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Posted 17 July 2005 - 06:49 PM

Engine off, pedal is firm and high.

Turn the engine on, the pedal starts to sink, and in about three or four seconds is way down below the gas pedal reaching a firm stop just half an inch or so above the depressed clutch pedal.



I am no mechanic, never claimed to be, never will....that being said, IMHO, this sounds like a vacuum issue to me...

read this thread this morning, had to go into town later and actually paid attention to my brake pedal when i started the car - absolutely NO change in height.

call me an idiot if you like, but that is my 2 cents worth.

Hope you can get it sorted out soon, Hank. and just for informational purposes, let us know what it turns out to be when you do.

#23 NorthWet

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Posted 17 July 2005 - 07:16 PM

Could the booster diaphragm 'balloon' without actually leaking? So when the engine is running, it makes the total space available for brake fluid larger?...

Brake booster is not supposed to be in contact with the brake fluid; atmospheric pressure (or thereabouts, depending on venting) on one side, intake vacuum on the other. If reservoir is not getting low, losing fluid to the booster is not the issue. But if you have a reliably firm pedal with the engine off (and booster "drained" of vacuum), but a sinking pedal when engine is on, that sounds like the booster could still be an issue.

I agree with everything else about finding new failure modes, etc.

#24 MorganM

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Posted 18 July 2005 - 09:05 AM

Ignore that lady and her automatic Subaru; she obviously has no clue what you are talking about or she'd have had her brakes fixed already! I'm willing to bet she took them to that shop and ended up with the same results but actually belived the bull they are telling you... that is fine and normal. It's not!

Are they bleeding in proper order? How exactly are they bleeding your system? I've bleed quarts through my system and still had similar symtoms you describe. Simply drove me nuts! It barely felt safe.... brakes would fully enguage but I had to pump them up like you describe. I finally got my brakes back to normal using the cross directional patern getting that last bit of air out.

Demand all your money back from those dudes and go to another shop. It's not your master cylinder. I think there is still air in your system somewhere. You arent loosing fluid so you obviously don't have a leak. Air compresses WAY more easily than the hydrolic fluid in your brake system.

Remember your e-brake is cable actuated and seperate from your hydrolic system. It can and will stop you on your way to another shop! :drunk:

#25 Hank Roberts

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Posted 18 July 2005 - 10:58 AM

> started the car .... no change in [brake pedal height

Well, if you have a car with a vacuum booster working -- that's the specified test. You should notice a slight drop in the brake pedal, per the manuals, for a vacuum assist that's working normally. And there are several other steps for testing that.

None of the vacuum booster results allow that the "little decrease" in pedal height then continues slowly down to the floor though.

> bet she took them to that shop and ended up with the same results
> but actually belived the bull they are telling you...

The woman who insisted the brakes are fine, just like in her car, is the office manager/bookkeeper for the mechanic shop. She's the one I picked the car up from Saturday.

Berkeley has this problem with self-esteem. Way too much of it around.

Yeah, I plan to tell the owner that she's probably at the same risk of brake failure in her Subaru as I am.

It's apparently temperature-related -- I had the car out at 7 am this morning in the cold fog and the pedal still sinks when held down, but not as rapidly, and doesn't reach the point of going 'clunk clunk' on the stops at floor level in 30 seconds at a stoplight. Yesterday when it was hitting bottom fast and repeatedly, it was 80 to 90 degrees. It definitely gets worse when the car's heated up and the brakes have been used for normal driving for half an hour or so in hot weather.

So -- anyone able to recommend a competent Subaru mechanic in or around Berkeley, California?




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