yo,
As ELMO advised;
LOW PEDAL (Excessive pedal travel to apply brakes)
◦Air in hydraulic system - bleed hydraulic system thoroughly.
◦Brake shoes need adjusting.
◦Low brake fluid level - fill reservoir to proper level.
◦Poor quality brake fluid (low boiling point) - replace with approved fluid.
◦Broken front or rear hydraulic line (dual system master cylinder) replace hose.
◦Soft or weak hydraulic hose (expanding under pressure) - replace hose.
SPONGY BREAK PEDAL (Springy sensation to pedal upon application)
◦Air in hydraulic system - bleed system thoroughly.
◦Brake shoes need adjusting.
◦Poor quality brake fluid (low boiling point) - replace with approved brake fluid.
◦Soft or weak hydraulic hose (expanding under pressure) - replace hose.
◦Faulty check valves in master cylinder - repair master cylinder.
by OUR SPONSOR here;
Jeff's Bronco Graveyard
and here is the EVTM (prob by Haynes or Chilton)
It provides a few tests centering on vacuum supply to Booster
the entire Electrical and Vacuum Troubleshooting Manual (EVTM), Partial for a 79 & F Series
Source: by Ziggy (topsig) at
http://www.supermotors.net/registry/media/905065
Tests, to Pinpoint Elusive Brake Problems, Part 1, general
Source: by Larry H at
http://www.mightyautoparts.com/pdf/articles/tt82.pdf
"WHEN THE PEDAL GETS SPONGY
A spongy brake pedal is an indication of air in thesystem or a brake hose expanding under pressure. We have had good technicians swear that they ran a gallon of brake fluid through the system and still had a spongy pedal. Many parts get replaced needlessly, when only some basic checks are necessary to isolate the cause of the condition.
When diagnosing that spongy or dropping pedal, try these simple checks to isolate the culprit:
• First, make certain there is an adequate level of fluid in the master cylinder. If the fluid level is too low, then bleed the system before continuing. Make certain you follow the proper bleeding procedure, sequence, and recommended wait times between pedal strokes, if applicable.
• A quick test for air in the system can be accomplished by pumping the pedal 15-20 strokes, and on the 20th stroke, hold firm pressure on the pedal while a helper removes the master
cylinder cover and observes the fluid as you side step the pedal. A geyser of fluid confirms aerated fluid. Take precautions to ensure that the fluid does not come in contact with a painted surface.
• If bleeding of the system has been performed with no positive results, then isolating the trapped air or problem component will be the next step.
• Remove the lines at the master cylinder and plug the master cylinder outlet ports. A full pedal should be present. Sponginess or a dropping pedal confirms a problem in the master cylinder. Any presence of bubbles in the reservoir
is an indication of air being trapped in the master cylinder bore. If a full firm pedal is encountered, reattach the lines, bleed and proceed with the test.
• Isolating the trapped air to a given caliper or wheel cylinder is the first step in achieving a firm pedal. A small air bubble can be a nuisance for the technician when trying to obtain a firm pedal. Locating the trapped air can be accomplished with a pair of crimping pliers or two flat washers and a pair of vise grips. Restrict the fluid flow by pinching off the hoses (do not crush) that supply fluid to each caliper or wheel cylinder and check the pedal height following each crimp. Example: If restricting fluid to the right front caliper results in a high and firm pedal, it confirms an air pocket in that caliper, or a damaged hose expanding under pressure..."
Tests, to Pinpoint Elusive Brake Problems, Part 2, general by Larry H at
http://www.mightyautoparts.com/pdf/articles/tt83.pdf
=====================
Using vise grips often damages rubber hoses.. some parts stores may have a special Clamping tool for this job. such as this @ JEGS http://www.jegs.com/p/Stainless-Steel-Brakes/Stainless-Steel-Brakes-Hose-Clamping-Tool/1191260/10002/-1
