Frozen brake fluid or...?

A couple weeks ago, it was in the negative teens (dunno what that converts to in Canadian, but damn cold) My '04 WRX's brake pedal was rock solid, but no braking force, at the first stop I came to, on my way to work. It was fine after that first stop.

Yesterday, it was -2°, and my pedal was solid, again, for the first attempt at slowing down. So, thinking there might some moisture in the fluid that was freezing up, I flushed two pints of fresh fluid through the system. Put new pads all around, too.

This morning, it was 1°. I still had a solid pedal and no brake force.

What gives? :(

Brake fluid isn't supposed to freeze until -40C...

I was doing some research to answer your question and found some helpful answers to the same problem here:

http://forums.maxima.org/fluids-lubricants/579563-brake-fluid-low-freezing-points.html

Could there be ice on the pads, rotor or pins(that the calipers slide on)? Try riding the brakes for a few seconds after you get moving (with your left foot) to see if that solves it. If you really think it is the brake fluid, you could take a small sample and try to freeze it.

I bet it has more to do with the vacuum booster not working. Easy way to try and see (if you are that curious) is to pull the line to the booster and plug it. Try out the brakes. The fact that you were able to stop sounds like you were essentially driving with manual brakes in a modern car.

Ice on the pads & rotors make sense, as does the vacuum system. I hadn't considered those two.

Not frozen, but I'm sure the viscosity is higher. I dont have an issue with the brakes on my wrx, but the clutch feels completely different when its below 10*F until I get out of the parking garage and it warms up a tad, same with the steering.

http://my.cardone.com/techdocs/PT%2053-0002.pdf Similar issue?

I'd probably just ignore it, but I'm used to heavily salted, freeze/thaw winter conditions that make daily brake testing mandatory.

I just won an argument with a tech regarding a similar issue. Monday a Saturn Vue was brought in with a rock had pedal, let it sit in the drive for three hours and the car drove normally. Tech said "No Problem Found but it needs rear pads." I argued, I sold the client rear brakes and a flush. The client was not picking the car up until today so I bet the tech lunch it was the brake fluid. Tuesday morning was 7deg, he went to pull it in and the pedal was rock hard. We replaced the fluid and set it outside. This morning was 3deg, the pedal was normal. We replaced the rear pads and I am enjoying a couple of Double Decker Taco Supremes and a Diet Mountain Dew ;)

In reply to John Brown:

Enjoying diet dew? Is that even possible?

Well compare it to your clutch pedal if it is a stick and the same fluid. Granted the hydraulic circuits aren't connected but if the clutch is stiff and the brake pedal is not at all, well what I'm trying to say is I have no idea but something else seems to be at fault.

My guess would be that sufficient water has accumulated in the brake system and it is the water that freezes. Brake fluid change, which like every manufacturer recommends every two years, will fix it.

beans wrote: In reply to John Brown: Enjoying diet dew? Is that even possible?

Not too mention, enjoying anything produced by Taco Bell as all I can think of is what will come of it later.... ugh.

John Brown wrote: We replaced the rear pads and I am enjoying a couple of Double Decker Taco Supremes and a Diet Mountain Dew ;)

Taco Bell food...so you lost the bet?

I'd sure aim at the booster. I can't imagine what you would be thawing by stepping on the brake pedal once, other than clearing up some ice in a vacuum check valve. Brake fluid would have to be very very damp to create anything more than a slow pedal. Is pedal hard if you step before moving?

Several years ago in the tatanuswagen ('82 Corolla Wagon) my clutch would not fully engage on a 0 degree (F) day. It worked fine when the outside temperature warmed up later.

My theory is that the brake fluid in the clutch had sucked in lots of ambient moisture (like it does) and lead to freezing and blockage of the hydraulic circuit.

That's the only time I've ever had that happen in a vehicle.

Well, after work, I stepped on the brake pedal before moving the car. It felt normal. Drove down the street, and it was solid again, but went to back to normal after a second pump. It was about 9° with blowing snow. Each time, the clutch was normal/fine/no issues.

1988RedT2 wrote: My guess would be that sufficient water has accumulated in the brake system and it is the water that freezes. Brake fluid change, which like every manufacturer recommends every two years, will fix it.

I did change the juice, last night.

i have no idea when my brake fluid was last changed- if ever- on my 01 GTP, but my brakes worked fine when it was -27 (without the windchill) a couple of weeks ago and when it was -18 yesterday morning.. the PS pumped groaned for a few seconds when i first started it, tho..

in the brake development world, we do "ice box" testing where the car is left in a, you guessed it, ice box overnight, about -30 C. the ice box is located so the car can be driven straight out onto a test track, where pedal force and deceleration is measured. it is normal for the vehicle braking system to have longer-than-normal response time at those temps due to higher viscosity of brake fluid, but being forced to flow through the small orifices in the MC and the ABS unit, plus underhood heat from the running engine, typically makes this a one-stop-only effect. because we do this on new vehicles with new fluid, i can say pretty confidently that it is not water droplets freezing in the brake fluid.

Last week we had temps ranging from -3 up to 5 and the first stop in my F250 was almost no bite, once the pads and maybe fluid warmed up just a little it was fine. I would guess the combination of super cold pads and fluid could be the problem.