No Brakes When She's Cold...**Update #1**
 

I start the car in the morning nad I have my power assisted brakes. I pump the brakes 3-5 times and it's like I have shut the car off and have manual brakes :? Then after 5-15 seconds, the brakes function normally.

Only happens on a cold morning, +20°F and colder

I have never bled the brakes, never needed to.

Do I need to, or should I bleed the brake system?

Vaccum lines?

Does my car not love me anymore? :cry:

Thank You :D

It scared the (fill in the blank with a descriptive adjetive) out of me the other morning when it finally stopped in the middle of the intersection :shock: Like it does me any good to the car stop there :lol:

vaccum leak to the booster?

Failing brake booster?

Random guesses.

Those would be my guesses, also. Check for cracks in the large vacuum hose leading to the booster, or at the connection to it.

How many miles on the car? Is it the original master cylinder?

that doesn't sound like the MC neccisarily. If that was the case, then the pedal would go all the way to the floor, even if the engine was off. the pedal wouldn't have that hard feel.

I would say definitely something to do with the brake booster. possibly failing, or maybe just a leaking vacuum line.

179K on the car and I have not changed it since I bought it at 95K

Should I change it and have the system bled out?

I will check the vaccum linse and feel for a leak as best as I can - probably just swing by the parts store and pick up a new hose.

Thanks for all of the input - keep em' coming :D

Ok, went to Shucks, popped the hood and checked the vacuum line (running from the PCV on the S/C to the brake booster) while the car was running. I did not feel any leaks.

Shut the car off, pulled the vacuum line off the brake booster check valve, started the car back up (it sounded like I had put an aftermarket cam in the car :lol: ) grabbed the vacuum line coming from the top of the S/C and put my thumb over it. It's not lacking any vacuum :lol: and the car resumed normal purring.

I think the check valve and the rubber grommet are on their way out. Shucks did not have it, so off to the dealer I went because I need brakes. The GM part #, if anyone is curious, is 18029764 for $22.80. It is both the check valve and the rubber grommet.

I also ordered a coolant recovery tank, pt # 25636828 for $19.09. How is the coolant tank cheaper than the check valve :? :lol: The one I have right now has a crack where the plastic was joined together and I am getting debris in the tank. :evil:

Thanks for all the replies! :D

Given the fact that it only happens when it is cold, it sounds like water in the lines. Have you bled them yet?

The reason I ask, is that I have a similar problem with the clutch in my Isuzu Trooper as it is hydraulic. I found that the cap on the hydraulic fluid was letting in moisture and causing spongy clutch and to partially freeze when it gets real cold. I think it may be suspect because when I replaced my master cyllander, it did not come with a new resovour(spelling?).

This sounds like it's booster related. Once you get the parts and swap them out..please post the results.