last two rides I've experienced issues with my brake cables. Both front and rear, but the rear is more extreme.

After about two hours in -5 to -7° celsius, my brake cables seem to get sticky in the housing. When I release the brakes the front brake slowly opens and the rear releases the tension, but continues to drag on the brake track. At stops I'm having to reach back and manually open the brake. It's definitely the cable or housing. If I squeeze the caliper together by hand it snaps right back when I let go. After warming up indoors for a bit the brakes behave normally.

Cables and housing were replaced this spring and are the same brand that were previously on the bike. I've rode in much colder temperatures and never had this problem.

I took the cables out and blew out the housing with compressed air thinking there may be water in the housing that's freezing, but that didn't solve the problem.

I've ordered some T9 waterproof lube as a last resort so we'll see if that fixes the problem next week.

Could this just be a bum set of cables/housing? The cable itself looks perfect, no rust or fraying, but I obviously can't inspect the inside of the cable housing.

If the cables operate normally at warm temperature, then the cold temperatures must be impacting normal operation. Identifying which material causing the problem will require a little testing. Some possible deleterious conditions are 1) existing lube in cable housing (especially wax based) affected by temperature, 2) cable length shrinking due to temperature difference, 3) condensation in housing, 4) cables may be operating in warm temperature at maximum friction loss capability of levers, in cold temperatures friction loss exceeds lever power.

It sounds like you have checked for water, but condensation could be trickier to eliminate. My guess is that the cables are rubbing somewhere and the cold just amplifies the problem.
Hope you find the problem and report back. I do a fair amount of cold weather riding and always need input to improve my winter rides.

I'd check out T9 cold temperature properties before using it.

Could be differential shrinkage of the cable and the housing. If the housing shrinks more due to the cold than the cable does, it could be getting too tight around the cable. Longer reach to the back would accentuate the effect, i.e. more friction for the longer reach. I would lubricate the wires with something that doesn't stiffen in the cold, like Teflon or silicone. That won't keep the outer from tightening on the inner, but will reduce the coefficient of friction. I have to say you may be fooled by the calipers snapping back. Try very gently releasing them, not snapping your fingers off the edge of them like opening a Zippo cigarette lighter (you have to be a certain age to understand this reference). Roughly releasing the calipers often causes them to open even when they would stick with a gentle release. It could still be the calipers needing loosening or lubrication at the center fixing nut.

But let's be honest about this. I doubt the brakes were designed with -5 to-7 deg C in mind. That is pretty rough cycling weather. More power to you, but I can only say I will never know if my own brakes have the same problem. Ain't gonna happen.

I had cables sticking on an old bike that had hardly been used but was old. i resolved it by blowing wd40 through the housing. it was good after that. in my case i think it could have been rust on the inner cable.

Rusty brake cables really ought to be replaced and not relubed.

The increased amount of friction in the rear brake, along with your good troubleshooting (caliper is okay, warmer temps is okay) screams to me freezing lube. The lube used in the cable housing is different than what it used to be. There may have been little/none before (with teflon lining that's not unheard of). I use a wax based lube and it seems okay.

Finally it may be that there is a bit of rough cut housing/liner which is okay when the lube is warmer and working well but the cold temps pushes it just beyond the cusp of smooth cable movement. The fact that both brakes are sticking says that this is not really the case. To check this you can loosen the cable anchor bolt and just slide the cables back and forth. You shouldn't feel significant resistance.

I'd clean the lube off the cable, "rinse" out the housing (WD-40 or similar solvent rich lube) and use a much thinner lube. I like White Lightning, it works well to about 20 deg F. Don't use as much lube as possible - that works well when it's pouring rain or you're going through stream crossing, but in cold weather you want a scant amount of lube so that there's room for the cable to move in the housing/liner.

Hope this helps.

If you have decent cables and housings, you shouldn't need any lube. In fact, it will tend to gunk things up which is what it sounds like you have.-5 to -7 C really isn't a big deal as far as cables are concerned.

Could be if you have lubed cable housings and due to temps. it getting thicker and creating the slower release. If it works any other time in warmer temps. I think it is a easy conclusion.

Lots of us ride in sub freezing all the time. No big deal and I can't recall having a similar problem. Maybe shoot some WD-40 down the housing, then it will finally get used for it's alleged intended purpose: Water Displacement.

Then maybe a little heavy oil on the cable instead of grease.

Do the levers move freely in the cold ?

yup. wd40.

This.

Now the liners are so scored that the drag will only increase.

It's time for new housing and possible cables.

Unless it's lubed cable issue, again wd40 washes out lube and moisture, the original stuff is not a lube. Messy. Have to take everything apart to do it right. Best long term easy fix is really good stainless cable and housings. Do it yourself with the right tools. Caveat - I have no idea what "really good stainless cable and housings" are, just what I've read here on BF.

I thought Yokozuna and may still be but had some shift issues when I used it to recable my bike. I went back to Shimano PTFE coated cables!

if you are intending on replacing cable and housing as people are suggesting, you might as well spray wd40 into the old stuff before throwing it away. nothing to lose.

True! Can't hurt to try and see for sure.

Easiest way to deal with this is never have old cables/housings. If you replace them regularly, chances of heads pulling off, cables seizing, or even decreased performance drops dramatically while you get a lot more miles without needing to fiddle with anything.

Another +1 to you. It seems we are of the same mind here.

Op, ideally, do the work once.

It is already too late for the housings, the damage is done. Spraying with WD-40 is a temporary fix that will still leave you with spotty shifting and then back to cruddy shifting again. Not a solution unless budget is an issue then this will indeed buy you some time to shop for a deal but shop you will.

Another consideration is where you are riding. If you are riding in a winter climate and there is a lot of moisture or road grime, I might just tough it out for the winter and live with the shifting (and a handy can of WD-40 and a compressor) and then install shiny new cables, housing and tape for spring.

Any way you go you will be replacing the housings soon, at the very least.

was gonna say clean and lube which you are doing. also not all cables/housings are created equal, but new cheap stuff can still be better than old better stuff.

Lube arrived today. They claim that it's good to -40°. I know I'm being cheap, but I would like to get these cables through this winter. I don't want to re-cable and re-wrap the bars just to do it again in four months when the spring comes.

A friend suggested that I also try trimming 10mm off each end of the housing which can't hurt and the housing is long enough to try.

Keeping in mind that cables that if shortening the cables sharpens the bends, your problems could be made worse...