Brake pedal sinks to the floor,

[Hank Roberts]

Google is my friend.

 

I don't know if this is a real clue. But I told the mechanic about it and he said -- if by some chance this is the problem with my car, and it could be, since the brakes were done by the previous owner -- they shouldn't have missed something like this. But, he thanked me and the Internet for the idea and they'll look tomorrow. As well as looking for an internal leak in the power assist. By the way, the brake pedal has a new sort of chirp as it goes down.

 

He did suggest it's possible there is a curse on the Subaru, also.

 

But he also agreed that the older vehicles are -- like us older guys -- going to be inventing new failure modes not seen earlier in life. So, I am going to give them another shot at it.

 

-----> The possible clue, as found searching the Web <-----

http://forums.corner-carvers.com/archive/index.php/t-4097.html

QUOTE:

"... The pedal is firm until I start the car and then the pedal will go soft and almost to the floor. ....

------------

" I had similar problems in my Subaru. Primary cause was ... I installed my calipers upside down (put 'em on the wrong side) and there was a pocket of air above the bleeder nipple. .... "

END QUOTE

 

I don't know whether to hope this is the problem, and has been missed for the past three months, or that it isn't the problem. But, it's a possibility. I'll let you know.

[Hank Roberts]

Ding.

 

The mechanic called to say they found at least one cause of the pesky brake problem. They've chased this since April, including replacing the master cylinder twice and bleeding over and over.

 

This time they found something new:

 

One of the front brake hoses going to the caliper was blowing up like a little balloon, once the car had warmed up (from the cool fog in Berkeley)

 

He says the other hoses are all good. I worry about that.

 

He says the brakes will still be kind of soft, that he compared another 1980s GL in the shop, but shouldn't slowly go down to the floor now.

 

I worry about that too. Old cars are old cars. Old hoses are old hoses. But dagnabbit the previous owner replaced all the hoses. Or did he ... Hmmm.

 

The mechanic called to say he thinks now that it's safe for me to take it for the weekend, after he did a 20 minute test drive. I'll pick it up tomorrow morning and go do a longer, hotter test drive.

 

(Next -- find out if the 20-50 oil in the engine solves the oil loss problem, before the rebuilt tranny comes back from CCR next week or two, in case I need a rebuilt engine from CCR put in along with the rebuilt tranny.)

 

The mechanic (in Berkeley) says he is very, very happy to have learned about CCR -- from me, after I persisted in pushing them to talk.

 

Crossing fingers, before starting engine.

 

Pray for me.

[MorganM]

Glad they found it Hank. I was gonna mention that as a possibility but I figured they had already checked for that since its really easy to check! Guess I was wrong in my assumption :-p

 

If you got the money have them replace all 4... bet the pedal feels even better! Don't belive what previouse owners say they'ev done unless you helped them do it

[Hank Roberts]

Picked up the car this morning from the repair shop, but the brakes aren't any better.

They replaced the one hose that was ballooning. There are seven more hoses, two per wheel, the garage owner says -- he confirmed he feels the pedal sinking as I do, and is very puzzled. He's going to get a different _brand_ master cylinder to try.

 

And I'm going to have him replace the rest of the hoses. I suspect it's a bad batch of hoses delaminating internally, just my hunch knowing how things can fail.

 

To check oil consumption (and pick up gear left with a friend after the last big breakdown, I drove it 260 miles today, all freeway.

 

New intermittent problem. ARGH!

 

Once at elapsed 30 miles, going downhill, first long hill on the freeway, just as I came over the crest and let up on the accelerator, decelerating -- wheel started shaking. Putting on the brakes the car pulled slightly to the left each time. Accelerating, the problem went away. I got to the bottom of the long hill, and after a few more freeway miles the problem disappeared completely.

 

Again at about 230 miles, suddenly, the wheel started shaking. This was on the flat. Accelerating made it a little worse; putting on the brakes didn't change it.

I waited til I had a lot of room around me (this at 65 mph) and did one fast hard brake pedal.

 

Problem went away within a few minutes.

 

I've read a few places since last week on the web about brake problems with hoses that -- rather than ballooning under pressure -- collapse when pressure is removed, and prevent the associated brake from releasing completely for a little while.

 

That would, I think, also happen if brake fluid leaks from the open center of the hose into one of the laminations, an internal bubble rather than an external bulge -- this is logic, knowing how other kinds of tubes with multiple layers can fail (including arteries, for example!).

 

But does this happen on auto brake lines?

 

This is getting damned scary. Could I now have a loose brake caliper dragging rather than releasing? It pulled to the left that first time, the one they just replaced the hose on yesterday was the left front wheel.

 

Same pedal sink problem remains. The car has great high pedal after driving a while, surprisingly high; when it's stopped for a while in traffic or signal, the pedal will begin to sink under firm pressure. And if I pump the brake fast, it comes up fast, and then goes down faster than ever. Same symptom complained of since April.

[Subsforever]

For the shaking i would guess that you could also have a loose lug nut, they may not have tightened them down properly at the shop, im guessing they had to remove the wheels to work on the brakes. I have had a shaking problem before after working on my brakes and not tightening the lugnuts enough. It would shake when not under power but go away when accelerating and gradually get worse over time until both deceleration and acceleration cause shaking. not sure why in your case it is intermitent though. i would check just to be sure that all the lugnuts are tight, could be a brake issue but not properly torqueing the lug nuts could be a possiblity.

Having a lugnut loose could have damaged the stud letting the lugnut work its way off to a certain point then becuase it cant go any farther slowly work its way back on, this is just a theory though not sure if it could happen.

[Hank Roberts]

Nope, checked, good thought though. This happened only twice, each time for only a few miles -- during more than a 200-mile trip.

 

The first time this happened today I was sure I had a tire coming apart, but the behavior went away before I had even moved out of the traffic lanes. I was on a long downhill, 4-lane freeway, just starting down from the crest when it started to shake the wheel as I tapped the brake.

 

I was thinking I had a low tire, a loose wheel, threw a balance weight off -- all sorts of things, except that hitting the brakes good seemed to make the problem go away, and it didn't repeat the whole trip north.

 

That first time it happened, I had a pull to the left when braking. The second time -- at the other end of the trip -- no pull to the left on braking. And for hours in between, no wheel shake at all in all sorts of conditions from freeway to steep paved country road up and down.

 

This kind of intermittent problem is what has had the mechanic at the local garage muttering that the car must have a curse on it.

[NorthWet]

For tire shaking, check things that could cause an imbalance or permit movement. Tire balance, obviously. Axle imbalance/wear (someone recently had an issue with bad axle causing a shimmy. A warped/hard-spotted rotor (though in my experience that only affects the actual braking). And my personal favorite, worn leading rod bushings. (Also known as brake reaction rods and a few other names.) These can allow some other perturbance to cause the control arm and leading arm to let the wheel oscillate fore and aft.

 

One wrinkle on your original brake problem: Yesterday while trying to start my stalled minivan on an upward incline, car in PARK ebrake off and foot on brake pedal, as I cranked the starter my foot on the brake pedal sank to the floor. I am still trying to reason out how low-system vacuum would alow that to happen when I do not recall it ever happening while the engine is just plain off and no vacuum is to be had.

[Hank Roberts]

> as I cranked the starter my foot on the brake pedal sank to the floor.

 

WHOAH!

 

That's exactly what's been happening to me -- just never had the engine NOT start promptly, so I don't know if engine ignition is required for this.

 

You just had the starter turn the engine over but no ignition?

 

Or the starter run but not turn the engine over?

 

I assume turning the engine over does the same thing for the vacuum system (momentarily) -- sucking air into the cylinders. If that is related to the problem.

 

Hill holder somehow? perhaps coincidence but:

 

The mechanic here just told me Friday that my hill holder cable was stretched so far that it could not be adjusted -- I'd noticed hillhold working to hold the car on one of our reallly steep streets in Berkeley, one that goes straight up the East Bay hills -- but that as soon as I started to touch the gas pedal the hillholder would go off and the car would roll back six or ten feet if I didn't catch the brake fast, before the clutch could get it moving forward.

 

So -- not sure if there's any connection here.

 

Maybe we have identified a new age-related Subaru failure mode with the brakes that is just starting to happen, mine has going on 240k on the odometer.

[NorthWet]

My "incident" was in a Ford Aerostar...

 

Low fuel condition, high nose up attitude, sucky fuel system design. I "ran out of fuel" with several gallons still in the tank, but none near the pickup bung. I was trying to get the engine to develop enough power for a moment to get to flatter ground, so I was "ready to roll" as soon as it caught. Engine cranked over, sputtered, caught died, etc.

[Hank Roberts]

Still no fix on this. I asked the mechanic to go ahead and replace all the flex hoses since they finally noticed that one of them was ballooning visibly.

 

I suspect the rest could all be a little soft (3 year old, previous owner replaced them, no idea whether OEM or 3rd party) and I don't trust them.

 

Mechanic wanted to try a different _brand_ of master cylinder. No response on whether that made any difference from them yet.

[Hank Roberts]

Another possible explanation: "air relief valve partially clogged."

 

I kept searching, and found this web page, which I recommend, it's not all there yet but the Subaru info is promising:

 

https://www.tocatta.com/subaru/index.html

 

"Subaru parts and Subaru maintenance. Not only do we show you where you can get parts for your car, we also describe how to diagnose and give repair procedures for many different types of Subarus."

---------------------

 

I've been swapping email with Andy Campbell, there, about this brake-pedal-sinks. He's spending significant time thinking it through with me. And I'm taking his suggestions to the mechanics who are holding my GL hostage now (while waiting for the CCR engine rebuild to come in, sigh....)

 

I think we now have three verified instances -- yours, mine, and his -- of this slow-pedal-sinking problem.

 

AND -- He has an explanation to suggest. He confirms the Subaru manual advice about testing the vacuum booster is accurate as far as it goes but it doesn't handle a partially clogged valve, and says he's seen this.

 

I'm going to post a fragment from his email and recommend his page as a place to look and ask. Maybe he's here too and I haven't recognized him.

 

 

QUOTE

"...Another failure mode of the booster, however, is to allow continual sinking after the usual drop and hold. This effect can happen if the air relief valve is partially clogged. Pressing on the brake in this case produces somewhat stiffer braking. After braking, air continuing into the relief valve produces more pressure on the braking system, and the pedal sinks further. Such a failure will pass the Subaru test. I actually found this once on a Dodge Caravan."

 

END QUOTE from his email.

 

Now, I have to figure out where the air relief valve is -- guessing it's a part of the brake booster that the mechanic's been so unwilling to suspect.

[Hank Roberts]

The answer was -- replace the brake booster. Problem gone.

 

Oh, first I had to replace the mechanic I was taking the car to.

 

I found a total of three mentions of this problem searching (both web and newsgroups).

 

Summary --- there's a little valve deep inside the brake booster that can get dirty. It's impossible to clean those things, though they can be rebuilt. This has been a known problem on some other manufacturers' vehicles, but not mentioned elsewhere on Subaru that I know of.

 

Well, as my MD keeps telling me, these old bodies find new ways to fail, the older they get, as things start to wear out that lasted 30 or 40 years consistently.

 

Yup.

 

The local new mechanic I've been going to said he'd only be willing to replace it with a new Subaru part. I said yes, tired of living with the problem, didn't want to push getting a rebuilt one vs. new. Life's too short.

 

Problem's gone, entirely.

 

Anyone need a good Subaru mechanic in Berkeley?

 

--> Autometrics. Ask for the guy who knows how to use the Internet. Tell them the guy who came to them because CCRInc sent him, sent you.

[EYE_WHY]

So the brake booster was the culprit??

 

I still have the same problems with mine, just bled them too and in the right sequence. No noticable change except that the pedal is a wee nibbin higher, but it still sinks to the floor with pressure. Should I have a local mechanic check out the brake booster????

[Hank Roberts]

The more common explanation for the problem, apparently, would be an internal leak between sides of the master cylinder, so you should get it checked.

 

I only know of three cars in the world that needed boosters replaced -- the 2 stories I found on the net that led me to this, and mine. So mechanics may laugh at you for suggesting it. One place claimed they tested it, but couldn't describe a test procedure, I doubt they had a clue.

 

Rebuilders for these things can be found; they know how to test them, apparently. I just got a new one, too tired of the problem to risk a rebuild.

[Hank Roberts]

One last thought about this general problem -- from a mechanic's page talking about Ford and Dodge brakes:

 

http://www.asaaz.org/canyonauto/techtips.htm#rust

 

"The Sinking Brake Pedal

 

"..... If you have a customer with a 1977, or earlier, Ford diesel truck complaining about a sinking brake pedal, and you are certain it is not caused by the brake master cylinder bypassing, it may be a normal condition. With the engine running, vehicle stopped, the vacuum pump may be pulling "excess" vacuum from the booster. The vacuum pumps on some earlier models continued to replenish booster vacuum, causing the sinking pedal condition. If this "normal" condition is unacceptable to your customer, Ford offers a replacement booster, PN # F5TZ-2005-CA.

 

..... This brake "problem" is old hat, but we still periodically run into the complaint. I first noticed this in the mid-1970s with Dodge pickups, and it has slowly progressed through all the pickup lines. The dreaded soft pedal!

 

..... Typically, what happens is right after a brake job, the customer "tests" the brakes by stepping (hard) on the brake pedal, with truck stopped. The pedal sinks, is spongy, or otherwise feels crummy. To really test whether you have a spongy pedal, dump the vacuum from the booster (engine off). Now step on the pedal: Is it hard, or spongy? Chances are it is rock hard, with no sign of falling through.

 

..... What I THINK is the explanation (I have asked numerous brake hot line techs this question, with no real affirmation, or denial, of the scenario), besides firewall flex, is the master cylinder construction. In late model tandem masters, the pedal operated primary piston, except through a spring, which in reality, it's not an operational spring. The spring's primary reason for existence is to simply keep the secondary piston in place. The secondary piston is operated by the hydraulic action of the primary piston. When the vehicle is moving, and brake operations are normal, the truck stops wonderfully (even with a bit of rear wheel lock up in a quick application), but the driver never notices any pedal problem. But stop the truck, apply the brakes, and pedal feels spongy. I believe what the customer is feeling is the spring action between primary and secondary piston, an action not typically felt during normal braking conditions. The trouble starts because many techs have never noticed this "problem" until the customer points it out. Then we go crazy trying to correct a problem that doesn't exist.

 

"..... However, I have no explanation for the Suburban brake pedal feeling. I mean, those felt terrible when the vehicles were brand new."

 

----

Just to confirm, the above wasn't my problem, just adding it for consideration when someone finds this thread.

[Hank Roberts]

So, Eye Why -- still here? Did you find your brake problem?

 

I'm back just to correct this:

 

... Subaru mechanic in Berkeley?

 

--> [not] Autometrics. Their manager told me their mechanics really don't like to work on anything more than 10 years old.

 

Instead -- Unitech, on Folger in Berkeley. Real, serious, good older Subaru mechanic there.