|
|
Posted by Paul(in NY) [12.64.134.185] on Sunday, September 12, 2010 at 09:57:56 :
In Reply to: close call! posted by Doc Dave [66.82.9.59] on Saturday, September 11, 2010 at 21:33:05 :
In two of the posts regarding rusted brake lines, the pedal went to the floor when the brake line failed. On modern vehicles with a dual chamber master cylinder, this is NOT supposed to happen. The front and rear brakes are actually separate systems, each being driven off the respective chambers in the Master Cylinder.
A brake line failure on either the front of rear axles, should be limited to only the
front or rear (depending on which line failed) and the other axle having brakes. The pedal will be lower, but its designed to not have a total failure.
So why did the pedal go all the way to the floor as in a Total System Failure ? Could the master cylinder be seriously blowing by ? Then this begs yet another
question.
On modern vehicles a brake pressure balance valve is found at the master cylinder.
Both brake lines enter this valve. In the valve is a piston that is centered and held centered by equal pressure on each brake circuit. If either circuit fails (such as a blown line) the pressure immediately becomes unbalanced, the piston is driven to one side of the valve or the other (depending on which line failed) and when the piston moves off center a switch is activated to illuminate the brake light on the dash to notify the driver of a brake malfunction. This brake pressure balance valve DOES NOT reset its self when the problem is corrected, it must be done manually.
And then on new vehicles with ABS, all this is intertwined through the ABS system.
What troubles me is that it appears that two of the vehicles mentioned might
have additional brake system issues.
1. The broken line allowed the pedal to go to the floor (Total Loss of brakes) This should not happen
2. The brake pressure balance valve did not switch on (piston move) with the unbalance of brake pressure and illuminate the dash warning light.
Paul
Follow Ups: