Voyager 2000, brake fluid boiling

"jmom" wrote

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