Voyager 2000, brake fluid boiling

Recently I was driving down a long hill. At the end of the hill I
noticed that the brake pedal was kind of spongy and a few meters
ahead, the pedal just went to the floor without stopping the car
(luckly I was driving very slow when this happened!). I was able to
stop to car using the parking brake, and a mechanic took a look at
it. He told me the brake fluid boiled because of excesive use while
descending the hill and that it caught some air, and that he needed to
bleed the system to get the air out. He also said the rear brakes were
not "well calibrated", so all the work was being done by the front
brakes. So he proceeded to bleed the brakes and properly "calibrate"
the rear brakes, he added some more fluid (generic "heavy duty", it
was in a rural area in mexico and that was the only thing available).
I was very paranoic for the rest of my trip, but I didn't have any
other incident of losing the brakes. But since that day, the ABS light
some times comes on after 30-40 minutes of moderately traffic
(randomly, not every single time).
Another mechanic that looked into it told me that ABS brakes should
never be bled (the way he did) and that was probably the reason why
the light is coming on. I was more concerned about mixing up the brake
fluid.
I bought this vehicle with 17K kilometers on it (at least that is what
the odometer says, but in mexico you never know), and I don't know
anything about the services that were performed on it.
Any ideas from the experts, as to what could cause the light to come
on?

TIA

 

Classic case of brakes "fading". Use a lower gear so you don't have
to ride the brakes. Bleeding the brakes is the right fix.

The front brakes always do more work than the rears. It's also easy
for the rear brakes to not do their job, especially for drum brakes.
The proportioning valve is IME *NEVER* right. However, all drum
brakes are self-adjusting and (it sounds like) he didn't replace the valve,
so you got ripped for the "calibration".

There are special procedures to bleed a system with ABS; probably
he didn't follow them. Have a shop you trust, or specialty brake shop
or the dealer shop ($$$) do a brake fluid flush. That will take care
of any concerns you have about brake fluid quality (personally,
I wouldn't worry - brake fluid is brake fluid in most cases.)

Floyd

 

In the first world, virtually any commercially available brake fluid meets
the legal minimum specs.

The original poster is from (and in) Mexico.

DS

 

Did you downshift the transmission while descending the hill? I haven't
checked my van owners manual lately, but many recommend you downshift on
a long hill to assist the brakes.

It almost sounds like the fluid was contaminated with water. I'd have
the system flushed and bled properly.


Matt

 

Correct me if I am wrong, but I thought it not wise to mix DOT3 and DOT4
fluid?
Not that this would even count in Tijuana I guess!

 

DOT 3, DOT 4 and DOT 5.1 are fully and safely intermiscible.

It is DOT 5 (silicone-based fluid) that mustn't be mixed with any other
brake fluid.

 

Conventional brake fluids absorb moisture which eventually lowers their
boiling point. Unless conditions are severe, this is good because when it
is cold, the absorbed water doesn't freeze. However, under severe
conditions the fluid is more likely to boil. When it boils, you run into
the problems you described on the hill. Some car companies suggest the
fluid be changed every two years. Others allow it to go longer. It may be
that the front brakes had to work especially hard on the hill because the
brake pressure equalizer for the rear brakes wasn't working correctly. It
may be that rear brakes (usually drums unless an all wheel drive model)
weren't adjusted properly or were not functioning. If they didn't work
well you might not even notice because the front brakes may have normally
picked up the slack. It may have even been the case that the system was
normal and that your load, the hill, weather, and your driving style were
too much for the weak brakes on these cars. Taking the car out of drive
certainly would have helped. In any event I would definitely check the rear
drums, pads, and adjusters if drum brakes, and the pads and calipers if
discs are on the back. In addition, I would check the pressure equalizer
between the front and rear brakes.

It seems to me the mechanic who worked on the car may have not been too far
off. It sounds as if he adjusted you rear brakes, added fluid and bled the
system.


As far as the ABS light is concerned, brakes can usually be bled without
upsetting the ABS. However, if the fluid in the ABS unit is disturbed by
conventional bleeding, or conventional fluid flushing, you will have
trouble. The factory manual gives the procedures for flushing the ABS
correctly, and it is not easy. You need a dealer or a real specialist.

In any event, after a fluid boiling situation, I would want to have my
system checked, completely flushed, and refilled with fresh fluid. This
means a trip to a dealer, or a specialty shop who knows how to do the job
correctly.

 

It almost sounds like the fluid was contaminated with water. I'd have the
system flushed and bled properly.

The brake fluid used in most cars (DOT 3) is highly hydroscopic. That means
it is a chemical mixture that absorbs water. It is essential to flush out
the system once in a while to remove the moisture. DOT 4 is a bit better and
fully compatible with DOT 3. DOT 5 is silicon and is not hydroscopic, is
vastly superior, but is not compatible with Hydroscopic fluids. If the flush
is not complete the DOT 5 fluid will actually trap in moisture; and may be
incompatible with some older calipers, etc.

DOT 5 should have been a standard feature for 10 to 15 years already, but
only a few cars have used this grade of fluid.

Richard.

 

No, because water absorption is actually desirable in some situations,
such as cold weather and steel brake lines. With silicone fluid, any
moisture that gets into the system doesn't mix with the fluid, but
settles into low points in the system. There it can either freeze or
rust the brake lines from the inside out.

Don't confuse different with better.


Matt

 

Oh; so I guess the airforce, airlines, and the NATO/Military motor pool guys
don't know what they are doing. Same with some very top of the line motor
car venders?

Richard.

 

Richard, Matt is correct. DOT 5 is not "vastly superior" across the board.
It has a higher boiling point than DOT 3 or DOT 4, but the lack of water
absorption ability *is* frequently a liability, for exactly the reason
(and with exactly the results) Matt described. DOT 5.1 gives the same
ultra-high wet and dry boiling points as DOT 5, but without the marked
difference in water interaction compared to what virtually all automotive
brake systems are designed for.

There is also the issue of DOT 5's tendency to trap microfine air bubbles
-- this is definitely not a "vast superiority".

As far as the air force and other military bodies: Is your vehicle painted
olive drab? Does it have a 28v electrical system and 8-ply tires?

No? Well, why not? I mean, the air force and NATO vehicles have all those
things...

 

I doubt you will find plain steel brake lines on many airliners or
military aircraft. They are likely stainless steel such that rusting is
much less of an issue. Also, airplanes spend a lot less time in contact
with road salt.


Matt