Just for chuckles why don't you try racing brake fluid and see if it makes a difference.

My 96 just did this this morning. 6 degrees outside, super stiff pedal and almost no braking.[...]Now, the funny thing is, I just did an engine swap on this car this weekend, so the vaccum hose to the booster was just hanging in mid air from saturday afternoon until sunday afternoon.[...]

Nipper has suggested that moisture freezing in the booster could be the problem, and I agreed with it being a possibility. Your experience would seem to support that. (Even with a "good" check valve, condensation might occur over time.)

 

That got me thinking; I wonder if applying a vacuum pump (like the ones used to evacuate A/C systems) to the booster's vacuum line for long enough could reduce moisture sufficiently to eliminate the problem. I don't know off-hand how much vacuuum the booster can tolerate, but if nearly 30 or so inches Hg can be safely applied for about an hour, that should eliminate most of the moisture in the booster; normal engine vacuum can be as high as 28 inches Hg or so during rapid deceleration.

Just for chuckles why don't you try racing brake fluid and see if it makes a difference.

In certain respects, some brake fluids designed for racing don't perform as well (especially long-term) as "standard" fluids. Since professional racers change brake fluid regularly, problems that occur with time aren't a big concern. If anyone is considering using a "racing" brake fluid for "street" use, I'd suggest reading the manufacturers info carefully first.

 

By the way, if it's DOT-5 (silicone-based), forget it; DOT-5.1 (PAG), maybe.

Yup, you'd have to pick carefully but some of those fluids are more resistant to temp changes and a bit different viscosity. Won't do anything of course if it is a booster or check valve problem.

http://auto.howstuffworks.com/power-brake2.htm

 

 

OK i see freezing as the cause. One side of the booster is exposed to moist cabin air, the other side to dry outside cold air. You Get this mix you get condensation. When the air is cold enough that condensatiuon freezes. Check valve doesnt have anything to do with it.

 

When it is below 35 the AC in the car does not work, so there is no way to dry out the air.

 

http://sg.answers.yahoo.com/question/index?qid=20070202205101AAz5pfN

 

I just searched the net and i come up with an unsatisfactory answer (flush the brakes). In that one article that stated that, the respondont just did a flush the year before. (he had a 2000 subaru).

 

Now there arew two failure modes. The one with the bad master cylinder, the pedal goes to the floor. The freezing Power Brake booster, you get a very hard pedal.

best i can tell is that we all need pwer brake boosters (im not sold on that). If there is no recorgnized problem, then there is no solution.

 

For now, DO NOT DRIVE BELOW 30 DEGREES UNTILL YOU HAVE A BRAKE PEDAL!

 

nipper

A block heater keeps the engine and compartment a bit warmer. Do folks with block heaters still have the problem?

A block heater keeps the engine and compartment a bit warmer. Do folks with block heaters still have the problem?

 

Cookie, when i use my remote starter i dont. When i just get in the car and drive i have a dead pedal.

 

Now keep in mind when i use the remote starter i have the heater on also.

 

nipper

That sounds like it could be a thrill. When I got my Chang Jaing the other day the first intersection was a similar thrill. I had the hubs powder coated and the did the inside of the brake drums too.

That sounds like it could be a thrill. When I got my Chang Jaing the other day the first intersection was a similar thrill. I had the hubs powder coated and the did the inside of the brake drums too.

 

HAHAHAHAHAHAHA

 

 

nipper

OK i see freezing as the cause. One side of the booster is exposed to moist cabin air, the other side to dry outside cold air. You Get this mix you get condensation. When the air is cold enough that condensatiuon freezes.[...]

Nipper, the way I'm reading what you wrote, you seem to be saying that you think condensation is freezing in the interior (atmospheric pressure) side of the booster (please correct me if that's not what you mean). Obviously, that would require a certain level of humidity in the cabin air. As I've said previously, I've never experienced the "hard pedal" problem on my '99, which you thought might be related to the model year. But perhaps it might be related to personal habits, in least in some cases. I try to knock as much snow/ice off my shoes as practical before driving; I wonder if some people wind up with saturated floor mats because they don't bother, and/or have passengers contributing to that. The cabin air moisture might be elevated quite a bit that way.

But perhaps it might be related to personal habits, in least in some cases. I try to knock as much snow/ice off my shoes as practical before driving; I wonder if some people wind up with saturated floor mats because they don't bother, and/or have passengers contributing to that. The cabin air moisture might be elevated quite a bit that way.

 

I don't think that has anything to do with it. There has been no moisture introduced through feet in my car in months. It sat for 4 months before driving it saturday to the garage, and then home again sunday night. Never had any snow on my feet getting in or out of the car.

 

What if the check valve isn't closed when you push on the brake pedal, you won't get any help right? Could it be a problem with the check valve being frozen or stuck in the open posistion?

Personal habits have nothing to do with it. We have zero snow here in NY (I WANT SNOW). The human body puts out a lot of moisture just sitting there breathing. Also when warmer moist air hits colder air you get condensation, and it doesnt take much ice to make a strong bond.

 

 

nipper

I don't think that has anything to do with it. There has been no moisture introduced through feet in my car in months. It sat for 4 months before driving it saturday to the garage, and then home again sunday night. Never had any snow on my feet getting in or out of the car.

 

What if the check valve isn't closed when you push on the brake pedal, you won't get any help right? Could it be a problem with the check valve being frozen or stuck in the open posistion?

 

http://www.howstuffworks.com/power-brake2.htm

 

check out the animation. You can almost see how donesation in the wonrg spot can kill the boost.

 

nipper

http://www.howstuffworks.com/power-brake2.htm

 

check out the animation. You can almost see how donesation in the wonrg spot can kill the boost.

 

nipper

 

I didn't realize I had to click on the picture to make it go. Now I get it.

It's such a pleasure to have open-minded discussion of the possible causes of this problem, rather than anyone deciding that they have all the answers.

I didn't realize I had to click on the picture to make it go. Now I get it.

 

neither did i the first time

 

From having rebuilt a few boosetrs, what looks like a small motion on the animation is even a much smaller motion in real life. So I can see how it would freeze. This still isnt right, but now that we are aware of it, we can make sure we dont mve the car untill the brakes work in bitter cold weather. Besides the engine will thank you for waiting a few minutes.

 

nipper

It's such a pleasure to have open-minded discussion of the possible causes of this problem, rather than anyone deciding that they have all the answers.

 

Damnit there goes my reputation ...

 

nipper

i've seen this same phenomenon on older generation Subaru's as well. a cause that suits a wide range of vehicles rather than model/year specific vehicles may make the most sense most of the time.

 

can dessicant be placed inside the brake booster? i've never had to replace one but i'm guessing probably not.

Trucks and busses use dryers in thier air brake systems.

i've seen this same phenomenon on older generation Subaru's as well. a cause that suits a wide range of vehicles rather than model/year specific vehicles may make the most sense most of the time.

 

can dessicant be placed inside the brake booster? i've never had to replace one but i'm guessing probably not.

 

The problem is on the atmospheric side of the booster, and there is no place for dessicant.

 

nipper

Trucks and busses use dryers in thier air brake systems.

 

 

Simply put (from a dryer mfg site)

Air has the ability to hold water in exactly the same way that a sponge can hold water, also the air around us contains water - in the form of vapor.

When air is compressed, water drips out in the same way as squeezing (compressing) a wet sponge. If you listen to the weather forecasts, they talk about low pressure fronts. When saturated low pressure air moves towards a high pressure front, the low pressure air gets squeezed (compressed) a little bit - it's going to rain.

If you let go of the sponge it expands back to its original size and now has the ability to absorb some more water. Air does the same when you expand it, it becomes drier and will readily absorb water from its surroundings.

And-------

(condenstaion)

An example is a window in a warm living room on a cold winter night. When the warm air inside the living room touches the cold glass, the temperature of the air in contact with the glass drops and water condenses out of the air on to the window. The bigger the temperature differential, the greater the condensation.

 

nipper

:banana:Success! On Nipper's suggestion, I removed the vacuum hose assy between the brake booster and the intake manifold. The check valve is embedded in the hose, so it's not something you can remove separately and replaced. It did appear to be sticking a bit (the old suck test), so I cleaned it with carb cleaner and dried it out with compressed air. The past 2 mornings, when the temperature was 10 deg F (yesterday) and 8 deg F (this morning), no problem at all! Had good brakes from the moment the engine started. Problem solved, at least for now! Though the car was in the garage those past two nights, the garage is unheated so it's, at best, only a couple of degrees warmer than the outside.

 

I'm not sure if this fix would solve everyone's problems, but you sure can't beat the price ($0). I'll probably buy another hose/check valve assy to have around in case the problem resurfaces.

 

Thanks for all the suggestions. This problem has been hanging around for over 3 (4?) years. I brought it up to the dealer's attention when the car was still under warranty, but they did nothing because they claim they could not duplicate the problem.

 

If anything changes, or if the problem comes back, I will post an update.

From http://www.ultimatesubaru.org/forum/showthread.php?t=29192&page=4 :

im wondering if there is some condensation freezing in the booster due to a bad check valve.[...]

From this thread:

[...]OK i see freezing as the cause.[...]Check valve doesnt have anything to do with it.

[...]

 

From this thread and http://www.ultimatesubaru.org/forum/showthread.php?t=29192&page=4 :

:banana:Success! On Nipper's suggestion, I removed the vacuum hose assy between the brake booster and the intake manifold. The check valve is embedded in the hose, so it's not something you can remove separately and replaced. It did appear to be sticking a bit (the old suck test), so I cleaned it with carb cleaner and dried it out with compressed air. The past 2 mornings, when the temperature was 10 deg F (yesterday) and 8 deg F (this morning), no problem at all! Had good brakes from the moment the engine started. Problem solved, at least for now! Though the car was in the garage those past two nights, the garage is unheated so it's, at best, only a couple of degrees warmer than the outside.

[...]

If anything changes, or if the problem comes back, I will post an update.

 

If nothing else, USMB is "consistently" entertaining.

Well, I had the same Phenom this morning, except this morning it was 7 degrees instead of 6 Anyhow, I 100% agree it's an issue with the booster/check valve. After two HARD presses of the pedal I had perfect brakes. I think I'll be checking my check valve tomorrow morning.

 

Keith

YAY we are on to something. I think ill wait for it to get warmer then 17 degrees to try it on mine too.

 

nipper