Hello everyone,

As I've been ironing a lot of the kinks out in my car, I've learned a lot about it. However, since the temperature has been getting to about 0C and colder at night, I've had a very strange brake issue.

The pedal is incredibly hard to press until the car has warmed up fully and has braked a few times. Until then, the brakes are hazardously laggy and stiff. It's as though there is no power brakes, but even worse as they almost seem to hesitate.

I think it might be a problem with the brake booster, or moisture in the brake lines. I can hear an airy sound from the pedal area when I press it, too. Anyone experience this in the cold before? It's getting dangerous to drive!

Thanks!

When was the last time the brakes were bled? I've heard of moisture getting into the brake lines. My goodyear tire shop were I get my cars aligned told me that I had moisture in my brake fluid and the system needed to be flushed. When I went to flush and bleed, the fluid was kind of yellow and the viscosity was a lot thinner than regular brake fluid.

Your issue could be since it gets pretty cold to where you are, the moisture in your brake lines are freezing....?

Sounds like that could be the problem or at least be contributing to it! However the fluid in my master cylinder is clear... I'm guessing that doesn't matter, though.

I was going to do a flush anyway, but how can I check if the brake booster is bad? The airy sound is worrisome and the pedal definitely has too much travel (fixed temporarily by pumping the brakes twice), but the pedal doesn't sink when I apply constant pressure.

Definitely do a good brake bleed with a buddy. While you are at it do the power steering (see my post on power steering above). And when you get all done and everything is working good take it to a good transmission shop and do the transmission as well. Drop the pan and replace the filter and put in good dexon IV synthetic. Use that same fluid on the power steering as well. Just suck the fluid out of the steering bottle and replace doing that about a dozen times. Take care of this baby as you will never find a newer car that is as good. Have fun with. Almost every time I take mine out I get complements. We are all lucky that own one.

EZ- in your PS thread you mentioned dexron VI, but in the post above dexron IV. Which one is correct?

Your problem when cold is not likely related to water freezing in the brake lines as it would not go away by driving the car.

Trace the source of the air hissing. This sounds like a vacuum leak.

It could very well be--but what role does the cold take in this situation? The brakes are fine until it hits 0C, at which point I have to warm the car up. I'm definitely going to do a good flush and bleed, but if there is a vacuum leak should I take care of that first?

Thanks!

Yes, your symptoms sound like no/low vacuum to the booster. No idea at this point why it's related to the cold.

I'm sure it could be both issues. I am doubtful of the previous owners maintenance...

What is a common area for it to leak? Should I check the brake booster in the bay or will I have to pull out the underscuttle for the dash?

The brake booster will have a rubber membrane inside it (that is the vacuum diaphragm). Just like the air suspensions fail on the x350s in cold weather, can easily see the same happening inside your booster. Or the vacuum line going to the booster is failing/leaking. My guess is after some engine heat warms it up the leak stops. Definitely agree with previous posters, find and fix the vacuum leak first.

I'll definitely check the booster out, and possibly the lines. I think I'm in need of a good bleeding, too...

I still find it weird, since it only happens when the temperature is 0 or below. Coincidence?

Thanks so much for your help everyone!