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Old 04-04-2016, 01:23 PM   #4
fdryer
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Join Date: Jan 2006
Location: NYC
Posts: 39,219
 

2003 L-Series 3.0L Sedan
Default Re: 97 SC2 (No ABS) Brake Pedal goes to the floor

When you drove the car with the parking brake applied, the rear brakes dragging and causing brake damage also cooked brake fluid. The overheated brake fluid expands and either expands to return fluid back into the master cylinder or has no place to go when brakes are applied (master cylinder ports are closed off to allow building up hydraulic pressure when stopping with the vacuum brake boost multiplying braking forces). Heated enough, brake fluid will boil and may create air as DOT-3 brake fluid easily absorbs moisture. Once this occurs, its wise to simply flush all brake fluid and replace it - a full system flush and bleed. Somewhere during this overheating phase, it may have damaged the master cylinder seals or at least the rear wheel cylinder seals, being closest to overheating brake shoes. Replacing both front calipers and one rear wheel cylinder leaves one more wheel cylinder in question. Remember, anytime brake fluid overheats, in this case with Parking brake applied for 10 miles, may cause more damage than can be seen. Since brake fluid doesn't let anyone know when it overheats, hot oil can cook rubber seals hidden from view. Replacing both wheel cylinders is just another procedure to eliminate problems. Brake oil seeping out the rubber seals on wheel cylinders is a tell tale sign of damage.

While your situation is completely different from another member here, its worth mentioning as a precaution and heads up warning. A member inadvertently put the wrong caliper on his front end resulting in air remaining in the caliper and unable to bleed it. It was determined he put this caliper upside down with the bleed screw towards the ground, effectively never allowing air to leave since air simply floats up, away from the incorrectly installed caliper. This new member didn't realize calipers are made for right and left side and simply ordered the wrong caliper. Even his close up picture was overlooked by everyone. A trip to a brake shop and about an hour of several brake techs butting heads determined the wrong caliper was installed with the bleed screw pointing down instead of up. Once this was clear, this member realized his mistake and hasn't replied........... Simple error but eluded everyone here.

The last wheel cylinder not replaced and a full system flush of all old brake fluid may correct this issue. NEVER use the engine for brake bleeding or flushing procedures. The brake vacuum boost unit multiplies brake pedal effort and can cause injury to anyone not aware of higher hydraulic pressures if a bleed screw is opened. Think high pressure when vacuum boost is used. Brake hydraulics are always flushed/bled with the engine OFF. You're probably not aware that all car brakes are dual diagonal systems - the right front and left rear are on one line of the two lines leaving the master, the left front and right rear are on the second line from the master. Master cylinders have two pistons, each one serving half the brakes. Dual diagonal brake lines are designed so in the rare case one line is damaged, only one half the brakes are lost. The remaining half can still slow a car down while not throwing the car sideways as the diagonal brakes prevents brakes from pulling a car to one side.

By creating an unusual situation, careful assessment of the entire brake system is needed to fully appreciate what occurred and what's necessary to restore full braking function back to normal. This may be one of a few exceptions where everything must be considered and replaced to remove and eliminate a sinking brake pedal.

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