Last year my 1998 Dodge Caravan needed new brake lines. This year we had to have the pads/rotors/drums replaced as well as a cylinder in one of the rear brakes. 2 weeks ago while driving down our hill to a major Highway, the brake pedal went to the floor and basically scared the shit out of my wife and daughter. We took it back to the place that worked on it and they bled and flushed the system, saying there was air in the system. Today, same hill, same lack of brakes. Back we go and now they are saying that it is either the master cylinder or the ABS brake valves. They can not tell which so all need replacing. To me this is awfully coincidental that this problem is occurring on the back of the recent work. They said there was no way to foresee these problems when the brakes were done. They didn't see this problem when the brakes were worked on. They did list a number of other things on the van that would need to be addressed in the future.

My question is: is this reasonable? Is it reasonable that these problems were just waiting in the wings or is this a problem created by them? Is this common? I have never had problems with master cylinders. This is my first vehicle with ABS. The brake system basically worked fine when it was first worked on. After their servicing, I loose my brakes twice.

If there is a thread on this subject, aim me to it. Thanks

Is it reasonable that these problems were just waiting in the wings or is this a problem created by them? Is this common?

My advice is to take the van to a second shop. It doesn't appear the shop you're working with is capable of diagnosing ABS or brake problems in general.

Here is an answer that I received from an automotive mechanic teacher who most likely taught a good deal of the mechanics where I live.

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Your problem is a common one and I have heard of it far too often. This is result of lack of knowledge by some auto technicians,perhaps not their fault ,but true never the less.

Here is the scoop;
When any vehicle has been in service for more than five to six years the Master Cylinder may be compromised. Under normal circumstances the pistons within the master cylinder only travel a short distance when applying the brakes. brake fluid is very hygroscopic and absorbs moisture. Over time this moisture falls to the bottom of the master cylinder piston bore and just lays there causing rust and sludge. as mentioned the pistons under normal circumstances only travel a very short distance and DO NOT come in contact with the sludge and corrosion. But... , once the brake hydraulic system is opened up and requires bleeding, pumping the brake pedal now causes the master cylinder piston rubbers to plow through the sludge and rust! This causes the rubber piston seals within the cylinder to become scored, scratched , and damaged. The results of this are not immediately evident but show up later. The symptoms include slow pedal leakdown upon light brake application and the pedal goes to the floor! The cause IS NOT air in the system. The pedal goes to the floor because the damaged master cylinder pistons causes the fluid to bypass the piston rubbers and the pedal goes to the floor. Upon a hard brake application the fluid will do the same but will not occur every time, only when under hood temperatures are high.
It is highly unlikely that the ABS system is causing the problem. I recommend you change the Master Cylinder with a new one and have your technetium do a brake hydraulic system fluid flush and fluid change. That should solve your problem.

As a final note : One should never conduct any service work to a brake hydraulic system that has been in service for more than five years without changing the Master Cylinder.

Reasonably good advice Mequa. However, if you change the brake fluid every two years or 24K, you eliminate the need to change out the MC. You can also buy brake fluid test strips at most auto parts stores. It's the rusty crud that kills brake calipers, MCs, wheel cylinders and ABS valves. If you change the fluid, they can last for, well, much longer than 5 years.

Well you went and did it. You got me all confused now. How have I managed to avoid any major brake problems without flushing brake fluid or changing a single master cylinder in 30+ years of owning 12 cars, possesing the majority of them at least 10 years, all while living in the midwest and northeast snow belts, England, and now a Socal desert? Am I just a lucky man?

I love your posts RIP! I also love a good challenge. I guess you know what article I'll be adding to my blog this weekend!

You know, it never used to be such a problem. But these days, with very delicate valving in the ABS assembly, any dirt or grit can really foul things up. Honda and Toyota have brake fluid changes listed in their maintenance manuals. Domestic car makers simply ignore the entire issue.

Theoretically, a brake system is a semi-sealed system. The only time it's exposed to air is when you check or add fluid or do a brake job that involves opening a line. The MC has a rubber gasket, the calipers have a square cut "O" ring, the wheel cylinders have rubber cups, and the flexible brake lines are made out of rubber.

But think about this: As wheel cylinders fill with fluid, hydraulic pressure pushes the rubber "pucks" against the metal push piston. (the piston pushes the rod, the rod pushes against the shoe) The pucks have a lip seal that theoretically squeegees against the bore of the wheel cylinder. But the bore on the side opposite the fluid is always exposed to outside air. So, as the rubber pucks wear, they actually pick up some of the outside moisture and drag it into the fluid side of the cylinder. The fluid absorbs the moisture. The moisture causes rusting. The rusting turns the fluid brown.

It also turns out that the rubber seal in the MC isn't as air tight as we were led to believe.

As if this isn't enough, brake fluid contains corrosion inhibitors. They wear out and corrosion sets in.

The two brands of test strips on the market operate differently. One brand measures H2O levels in the fluid. The other (supposedly more reliable) test strip measures copper content in the fluid. That company says that as the steel component in brake fluid lines deteriorates, the concentration of copper in the fluid increases. So a high copper content is a sign of steel degradation and fluid exhaustion.

Try these links:

http://www.phxsyss.com/tutorial.html

http://www.babcox.com/editorial/bf/bf40142.htm

http://www.search-autoparts.com/searchautoparts/article/articleDetail.jsp?id=8027

Rick