Determining if there is moisture in the brake fluid? Hot wheels... literally

[Camry LE 94]

I got my brake fluid flushed during last Winter because my BRAKE light came on. After the fluid exchange, the light went off...

A month ago, I went to get my oil changed at Firestone, and they informed me that my brake fluid had excessive moisture in it. They said they tested it, and showed me a small strip containing a sample of my brake fluid and said it was the worst possible...

My brakes do make the front rims very hot, especially during the warmer months. Could excessive moisture be the culprit of this rim heat? Or is the only culprit dragging brakes, where-as the slider pins need to be greased again? Brakes are new, but did not grease the slider pins during installation.

[hill8570]

Hot rims are dragging brakes, not moisture.

Excessive moisture will cause severe brake fade (your brakes won't stop worth a crap after a couple of hard, high-speed stops, due to the moisture turning to steam in your brake lines).

Seems unlikely you've got much moisture in the lines after only a year unless the shop who did the original flush where total incompetents.

IIRC, the "dip strips" don't test for moisture, they test for copper, with the thought being that if there is excessive copper the fluid is corroding the brake lines and needs to be flushed. I've got mixed feelings about those -- in theory they sound good, but if you browse the internet, there are tons of shop testimonials of the form "I've had lots more flushing business since I've starting using these strips", which kind of implies to me that the strips are too damn sensitive.

[93celicaconv]

Either your caliper pins are binding, your your caliper pistons are binding.

Typically, whenever the calipers are removed for whatever purpose (like installing new pads, or just inspecting), I always remove the pins and lube them. Toyotas aren't known to have great calipers due to pins binding, so I always lube them. And most times, they are already starting to rust and bind when I remove them.

If your wheels are hot already, you must be getting poor fuel mileage. You will do much better when you remove this drag on the wheels.

[73sport]

In short moisture will kill the system and in my experience, where there's moisture there is almost always air. Air and water expand when heated and could cause your brakes to drag. Sitting in traffic underhood temps hit the lines under the hood and in the wheel well and can play a role even if your not using your brakes heavily.

That is not to say that you don't have hung calipers, you may and it is more likely that this is playing a role in the hot wheels. << EDIT >> "This" being either calipers don't float or slide or pistons not returning all the way.

As for the home DIY's: that aged bottle of brake fluid should be thrown away. Brake Fluid absorbs moisture from the moment you open it and simply opening a bottle on a humid day and or topping your system off on a humid day adds moisture to the system.

Always open a new bottle. Try to do it dry low humidity days. Get your system flushed at least every two years to remove sediment and moisture to prolong the hydrualic components.

You should be able to freely spin the wheels anytime the wheel is off the ground. If this is not the case, inspect, clean and make what ever repairs are needed to free up the rotors.

[Stillrunning]

Originally Posted by Camry LE 94

They said they tested it, and showed me a small strip containing a sample of my brake fluid and said it was the worst possible...

No need for a "test", just look at it. Cloudy means moisture. Here in NC I have to change brake fluid once per year due to humidity. Up north probably not quite so often, but good practice just the same. Easy to change yourself with a helper.

[AlmightyCamry777]

if your brakes are hot, one of the first things to suspect is sticking piston in the calipers. Your car is 14 years old, you might want to think about replacing the calipers with new/rebuilt ones.

[JohnGD]

Maybe that Firestone shop didn't know you had it flushed last year.

One reason the brake light came on was because the brake fluid level was low in the reservoir. In a properly working brake system, this would also coincide with brake pads/shoes near minimum thickness. Otherwise, the mechanic needs to check for leaks in the system before blindly adding brake fluid into the reservoir.

So if a shop recommended a brake fluid flush only because the light came on, then they're less than honest.

Unless you have problems with the reservoir cap or other rubber components, you generally shouldn't reach 3% moisture content until about 2 years after getting a proper flush, especially if you are using a decent fluid like Castrol GT LMA (low moisture activity) or Valvoline Synthetic brake fluid (not to mention ATE Gold 200, etc). However, poorly maintained shop equipment could dump moisture-laden "new" brake fluid in there. See if the shop is willing to test your newly flushed system.

If the rims got very hot but the calipers were properly lubed and sliding, then I would suspect the square-cut seals in the calipers weren't doing their job in retracting the pistons. It's probably time to rebuild the calipers and wheel cylinders. I do them on a preventative basis, and of course I flush the old fluid out every year. About $7-9/quart (~$14/litre for ATE). Cheap enough.

It's easy to check if the caliper pins slide if you're mechanically inclined and can do your own work.

Originally Posted by Camry LE 94

I got my brake fluid flushed during last Winter because my BRAKE light came on. After the fluid exchange, the light went off...

A month ago, I went to get my oil changed at Firestone, and they informed me that my brake fluid had excessive moisture in it. They said they tested it, and showed me a small strip containing a sample of my brake fluid and said it was the worst possible...

My brakes do make the front rims very hot, especially during the warmer months. Could excessive moisture be the culprit of this rim heat? Or is the only culprit dragging brakes, where-as the slider pins need to be greased again? Brakes are new, but did not grease the slider pins during installation.