Subaru no brakes when cold outside

I am desperate and have spent a lot of money and seen several mechanics now, i need help. For the past 3 yrs only in the winter when its around 30 outside where my car is parked after i start the car and put it in reverse to back up i have no brakes, the peddle is hard, i have to put direct pressure and hold it down til it softens to the floor after about 5 to 10 seconds then i have brakes for the rest of the day. But this winter and its still cold out it has been happening intermittently during the daytime going front or back i have to try and pump the brakes til the peddle softens or i just press the peddle hard and hold til it softens and then it works takes about 3 to 4 seconds in the middle of the day. Only happens when i first start up the car. I have replaced the pads, rotors, master cylinder, flushed the whole system and the latest money drop was replacing the booster. Please can anyone help me?

The booster replacement should have done it. Presumably that booster came with a new check valve. If not, scold whomever replaced the booster and have the check valve changed. Was the vacuum line for the booster also replaced? This line also has a port on the intake that it connects to, and that intake port needs to be checked for restrictions.

Just to elaborate for you, imagine that on the other side of the brake pedal is a vacuum cleaner and when you press on the brake pedal it turns the vacuum cleaner on and thus sucks your foot / the brake pedal to the floor. That’s more or less how the booster works, and if it doesn’t work the pedal feels really stiff and hard to press down to get braking force. It’s what it feels like to not have power brakes.

But the booster gets the vacuum power from the engine from a big black tube running between the engine and booster. The check valve is a doorway and lets the engine suck air out of the booster (so it has vacuum) but doesn’t let air back in (so it holds vacuum). Your booster check valve is probably freezing up or the whole connection is otherwise restricted so that the engine can’t create the vacuum in there as well as it should.

What year is this Outback?

Yes, the model year is a very important detail.

While the hard pedal is pretty sure to be an indication of a problem with the brake booster, the detail about the pedal going to the floor worries me that there could also be a problem with the master cylinder.

There was a recall of Outback & Legacy models from the mid to late '90s, for replacement of defective brake master cylinders, and the symptom was lack of braking ability in very cold temperatures. Because recalls never expire, if your car is one that was recalled but never repaired, if yours is one of the recalled lot, then you can have the master cylinder replaced at no charge by a Subaru dealership.

What is can you tell us about the model year and the exact model of your Subaru?

Its a 2003 Outback Legacy LL Bean edition 6cyl. the Brake mechanic was sure it was the booster so he replaced it. I will have to ask him about the check valve, intake port and vacuum line. I did replace the master cylinder and flushed the entire system last year it didn’t help. I wasn’t so worried because i have a long drive way and after 4 or 5 pumps to the pedal it would go to the floor and work fine after that. But now its doing it in the middle of the day where i am around other cars and its not freezing temps out so that is different this year. Thank you so much for your input i really appreciate it and would really like to get this resolved.

Just to clarify VDCdriver’s main concern, when you say the pedal “would go to the floor” do you literally mean that it goes to the floor of the car and bottoms out? Or do you just mean it presses down normally without the stiff feeling. The former case is very bad and is usually a master cylinder problem. The latter is just normal booster operation and is a matter of how you are describing it.

I have a new driver in the house and he normally drives a car with a very firm brake pedal. The pedal in my car is softer. He drove my car one day and reported mushy brakes. I told him to pump up the pedal with the car off until it felt stiff to see if it holds or sinks. It held. I then said to start the car and tell me what happened and he said the pedal went to the floor - by which he ONLY meant it sinks TOWARD the floor - once the engine runs and the vacuum assist kicks in. It was just his choice of language. Anyway - point is, be sure that the pedal is not literally bottoming out. And with the car off if you pump the brake pedal it will get that stiff feeling. And if you hold pressure on it, it should NOT sink. If it does sink then your car isn’t safe to drive. If you then start the car and the booster system is working, the pedal will sink - but NOT bottom out.

After i start the car put it in reverse i put my foot on the pedal and its hard doesn’t move and the car is still going backwards. after a few seconds if i either push on it hard several times it softens down and the brakes are working fine. Sometimes i have tried just to push on it with hard pressure and finally it will press down normally and then i have brakes that work fine.

I see what you mean if the car is off and i push on the brakes it goes down part way and the more i pump it gets firmer. I just backed up and the brakes are working normally this am its 45 out.

What about the brake self adjuster?

Your car has disc brakes on all 4 wheels, so there is no self-adjuster as you had on older cars with rear drum brakes.


Have your mechanic squirt some penetrating oil on the hinge point of the brake pedal.

is this something i could do myself?

I am not aware of any peculiar issues with Subaru power brakes but the vacuum booster on the vast majority of automobiles would have such a problem if moisture were anywhere in the booster circuit. There is a relief with a filter around the brake pedal plunter and a check valve at the vacuum supply hose and if either is damp it can block air (vacuum) and cause the pedal to be high and hard while not holding the car against the engine.

maybe replacing the booster wasn’t enough sounds like there are a few components attached that may be a problem i am taking it back to my brake guy next week i will be sure to mention everything everyone has mentioned thanks so much

If you are up to contorting yourself into a pretzel like position, then get a can of PB Blaster or Seafoam and crawl around under the dash so that you can see where the brake pedal pivots. The re-contort yourself so that you can aim the spray at the hinge/pivot point. Be careful to not get any in your eyes, maybe wear goggles.

Also spray the hinge point where the piston rod from the booster is attached to the back of the brake pedal.

It’s a lot easier for the mechanic with the car up on the lift, all he has to do is open the door and lean in.

Ha good idea i may leave that for the mechanic next week. thanks for the idea. i am writing all these down for him.

Ha cigroller you are so smart. After spending over $1,000. in r/r’s on my brake system it was in fact the $25.00 booster cable that they hadn’t replaced when they put in the new booster. Dang I hope this helps some other poor unsuspecting soul. thanks wish i would have known about this site sooner.

@CindyLouHoo, everyone gets lucky once in a while! Thanks for reporting back - we often never find out what happens. I’m so glad that you have it fixed. But so sorry that you had to go through the ringer first. Best wishes.