I have a weird problem with the brakes on my 2009 Jeep Grand Cherokee. It seems like it is related to the snow and ice. Maybe an ABS thing. When I step on the brake, I feel a little resistance, but it goes down much further than usual before I really feel resistance and I feel the car start to slow down. I definitely notice it when there is ice on the road, but then it mysteriously resolves when the weather improves. The pads look okay. There is fluid in the cylinder.
What you are feeling is your abs trying to prevent locking your tires. The delay in slowing is the tires re establishing grip.
Nothing to worry about. Drive accordingly.
Nah, I know what you are saying. buy it’s not that.
Then describe your problem better.
Is the brake warning light “ON” ?
To my mind, that is the classic symptom of a worn-out master cylinder. If you have sufficient fluid, but are experiencing those symptoms, I strongly suggest that you have your mechanic check the master cylinder–before you wind-up with really serious brake problems.
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I am also suspicious of the master cylinder. However, I am wondering whether it is truly an ice/snow problem, or is it really a cold weather problem.
Have you checked to see if you are losing fluid? If there is fluid loss at one wheel, that also might have this symptom.
+1
Because the seals in the master cylinder shrink slightly in very cold temperatures, I think that this points to a cold weather problem, rather than an ice/snow problem.
It could be a cold weather thing. Yeah. That’s totally possible.
I haven’t noticed any fluid loss. I’m kind of skeptical that it would be that because the reservoir is still full.
Worn out master cylinder does kind of make sense. I have about 100,000 miles on there. So she’s getting up there, I guess.
Is there any way to “check” the master cylinder? I think my mechanic would just be like, yeah, we can change it for $1000 and see if that helps.
I’m not getting any warning lights at all.
When it’s cold and the brakes act up, open the hood, and heat the master cylinder up with a heat gun/hair drier.
If the brake pedal is no longer spongy, replace the master cylinder.
Tester
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I do feel like the ABS has been coming on a lot lately. I wonder if I’m losing pressure in one whole circuit. I think that would explain the pedal going so far down and it would also cause those wheels to lock up more easily and trigger the ABS.
I just put plastic film over the windows in my office here to block the draft. I literally have my heat gun sitting on my desk. Why do I not think of that? 
I agree with Mustangman, I think you are just feeling the normal operation of the ABS. The Abs is preventing lockup because the road is slippery your car does not feel like it is slowing as fast as it should so you are pressing harder on the pedal harder, but the abs is still preventing lockup so to you it feels like the pedal is spongy.
If your mechanic would charge that type of price for replacement of a master cylinder, then I respectfully suggest that you need to find a new mechanic.
A knowledgeable mechanic can test your master cylinder to determine if it needs to be replaced, and if it does need replacement, the total bill for both diagnosis and repair should be a mere fraction of $1,000.
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Yeah, I just pulled a number out of thin air. But that’s good to know.
I know. That would kind of make sense. But I have driven 60,000 miles in this car. I know what the ABS is supposed to feel like. There is something else going on.