Question about brake failure

[meck]

A rear brake line broke yesterday on my '94 Ranger, and I was left with no brakes at all. I thought the dual master cylinder setup on vehicles was supposed to leave you with brakes on two wheels if a line broke. Why did I have no brakes? What happened yesterday felt no different than what happened to me long ago on an old '64 chevy that predated the dual master cylinder.

 

[alwaysFlOoReD]

How did you come to a stop? Your e-brakes worked? Im my experience the pedal drops down quite a ways and the pedal will feel like nothing is there until you press a lot harder.

 

[adsm08]

The dual chamber master does leave you with operational brakes on the side that hasn't experienced the failure, but since the pedal feel is dependent on the whole system being sealed you will loose all pedal feel.

Also, since the chambers can't be sealed from each other perfectly you will loose performance.

 

[Mark_88]

Yeah, they can go very suddenly under some circumstances. If it's the rear lines broken you will have fronts until the master runs out of fluid...and the light on the dash will light up if that sensor is working properly.

You can plug the line at the master if you have the right sized bolt or plug and drive home using the fronts only...but only if you can be sure the fronts are working and only in an urgent situation...like no money for a tow.

I actually did this and ended up driving for a few months once...but didn't like the idea that I was doing it (so don't do it, right?).

 

[meck]

Well, it doesn't sound, then, like the dual master cylinder is worth a whole lot in terms of safety. I hit the brakes, they went nearly to the floor. Went for the ER brake and got stopped on the side of the road. Looked under and saw the fluid coming out. By the time I got back in the truck, there was no pedal at all. Thanks, though, for your answers. Somehow, I had come to think that I was protected from catastrophic brake failure. Guess I was wrong.

 

[adsm08]

It is better than the older designs, but it has it's limitations. It is especially limited in the event of rear failure. Modern systems have a proportioning valve that keeps the front brakes from engaging until the rear system pressurizes unless the pedal goes past a certain point. And as we have already pointed out, it doesn't matter how things work you are still losing fluid from a sealed hydraulic system, so one leak and there goes your pedal feel.