Ken, that sounds totally wrong. In my books, impossible.

You can't compress a liquid.
You can compress a gas ( water vapor ).

Water in the lines means it can get hot enough to vaporize.
When you get vapor ( or air ) in a hydraulic system, the vapor compresses instead of the caliper, and you LOSE braking power... not get more.

I'm sure your brakes locked for some other reason.

 

But you are forgetting the vapor is steam because of the heat in the brake system. So what happens is you bear down on the brakes the temp comes up boils the fluid, makes steam which raises the pressure and the brakes lock. then when you release you have foamy fluid and it acts like air. The moisture can cause some swelling of the brake seals causing them to stick or hold and not release. Also if the calipers are made of aluminum there will be corrosion which also can swell and stick the piston. I have seem these things with my very own eyes.

 

My wife drives a 2004 X-Type Jaguar. I know that as part of the 20,000 mile service (which is done free under warranty) Jaguar changes the brake fluid for you.

~John

 

I am not contesting the "corrosive" or damaging effect of water in the brake fluid.
Water in brake fluid is definately undesireable.

FYI

Saturated steam at 212'F = atmospheric pressure.
at 250'F ~ 15 psi above atm
at 300'F ~ 50 psi above atm
at 350'F ~ 100 psi above atm

350'F may be enough to just "barely" get the pads to move against the disc/drum, if there was no way for the fluid to move back up the lines.
I read online it takes 75 psi to overcome the return spring.

Brakes in passenger cars and light trucks, when applied, can reach 1000 psi.
Brakes in heavy equipment, or race cars, can reach 2000 psi.

I think that steam, if any, in the brake lines would act like air in the lines, and give you a soft or spongy brake pedal, and add to pedal travel required to stop, since it will REDUCE the pressure... not increase it. But then, when the brakes are applied, and you get above 100 psi ( which sounds like every time you use brakes it is above 100psi ) the steam should be forced back into liquid, and you should be fine.

Probably why I can drive just fine, in summer, in the mountains, with a 20 yo car with 10 yo ( at least ) brake fluid.

As always, YMMV.

 

Since when does Aluminum rust?
I bought an old Insight because in addition to great MPG, the body is not ever going to corrode!

 

Disk brakes don't have return springs. You are correct that most of the time boiled brake fluid feels like air in the lines (my experience with cars) but most people pump the brakes before they realize what is happening. When you release the brake the pressure is released and the steam "boils" out. Corrosion is what I have seen on most motorcycles. Brake fluid temps normally get to the 325 range in stop and go driving or if the caliper is a little sticky it can go out of sight. You may have been lucky, but you have never had to replace wheel cylinders or master cylinders?

BTW if you keep a good coat of wax the Insite wont corrode

 

Please excuse the length of this post. I apologize in advance, but moisture in a hydraulic system simply do not mix.

Mark, our resident master mechanic, explained it well. Even a slight amount of water in a motorcycle hydraulic system can cause havoc when the extreme heat generated by the friction of the pads against calipers is radiated back into the wheel cylinder, and causes the minute water vapor to vaporize and expand. And believe me, it can happen very quickly. Unlike a car, it wasn't a case of spongy feel on the brakes, because I didn't have to actuate the brakes - the expansion in the wheel cylinder did it without my permission, at a very inconvenient time. The front brake was obviously the one affected most. Cycles utilize separate front/rear braking systems (two separate master cylinders). But when the front locks up, it raises the hair right on the back of your neck as it throws you forward and the rear of the bike wants to slip around to the front at the same time (momentum).

If this were to happen in an auto with 4 wheels on the ground, it wouldn't be nearly as dangerous as it is on a two wheel cycle, and you are surrounded by traffic. When my brakes locked up on the old cycle that day, I instantly wished I was back up at 3000 feet in the old Cessna 172, away from the traffic. (:

In my non-hybrid cars, where pads need to be changed more frequently, I've found this to be the most opportune time to flush/bleed the system. You are already sitting on the floor, working on the brakes, with your grubby clothes on. Perfect timing. Without fancy equipment, I simply use a hand vacuum pump with rubber tubing, being real careful not to allow air to be suctioned back into the line. I’ve been doing it this way for years with great success. You may need your wife to pump/hold the pedal to do a conventional bleed at the end, but that's no big deal. But you’ll probably have to take her to dinner that night.

Bottom line, if you ride a cycle, pay CLOSE attention to brake fluid condition. In a car, pay attention. Water and hydraulic fluid just don't play well together. I'm not an expert auto mechanic, but I've worked with both hydraulic and pneumatic gun drive systems for 28+ years on a daily basis. It's extremely hard to keep water vapor out of either pneumatic or hydraulic systems. In the industrial environment, filters, dryers, desiccant, pressurization, and many other elaborate measures are used to separate condensation from hydraulic and pneumatic pressurization systems.

 

Aluminum doesn't rust, but it certainly does corrode which really amounts to the same thing.

I had a small motor-home years back with an aluminum body. It had spots that where corroded clean through leaving holes in the body. It was not rust, but it really amounted to the same thing, a hole is a hole whether it was caused by rust or corrosion made little difference to me.........

~John