u: Brake / Transmission Vacuum Supply How the System Works . . . The system contains I power brake booster I automatic transmission vacuum diaphragm I vacuum reserve tank Power Brake Booster . . . Whenthe brake pedal is depressed . I valves inside boostersupply vacuum to rear of a diaphragm I the diaphragm is pulled back I this action gives an assisted force to the master cylindermaking it possible to brake the vehicle with less force I when pedal is released, the vacuum supply is ended and the diaphragm is vented Automatic Transmission Vacuum Diaphragm The vacuum diaphragm . . I is connected directly to intake manifold I engine vacuum controls hydraulic pressures inside the transmission I as engine vacuum changes with load conditions, vacuum diaphragm changes the hydraulic throttle pressure Inside the transmission the result is even, smooth shifting Vacuum Reserve Tank Because engine vacuum varies with throttle position . . I the reserve tank is used to store vacuum this stored" vacuum is used as a steady source of vacuum for components in the heater-a/c system temporary closrng of vacuum actuated components is avoided when engine vacuum drops Trouble-Shooting Power Brake Booster if a problem in the power brake booster is suspected . . . I check master cylinder fluid level If fluid level is correct. or additional fluid doesn't correct condition . . . I set engine at idle I connect vacuum gauge to booster feed If vacuum is less than 10 inches (Hg) . . . I check vacuum available at intake manifold I if less than 10inches,repairor adjust engine If intake manifold vacuum is at least 10 inches . . . I check supply hose to booster for damage or blockage lfhoseisOK . .. I check forvacuum leak elsewhere in system if 10 or more inches of vacuum ls being supplied to the power booster . . I place transmission in NEUTRAL I turn off engine I release parking brake I pump brake to exhaust vacuum from system I start engine. while applying pressure to brake pedal It brake pedal tends to fall away" . . . I the power brake booster is OK If no effect is felt under foot pressure . . r I replace the booster If pedal operation feels spongy underfoot pressure . t r I bleed hydraulic system of air Automatic Transmission Vacuum Diaphragm If you suspect a problem , t t I check and correct automatic transmission fluid level "this does not correct condition t . . I check vacuum available to diaphragm If it is less than 10 Inches (Hg) . . . I check vacuum available at intake manifold if intake manifold vacuum ls less than 10 inches . .. I repair or adjust engine If intake manifold vacuum is in inches or more . . . I check supply hose for leakage and blockage lfhoseisOK I check for a leak or disconnected hose elsewhere In system if condition still exists . . . I attach vacuum tester I vacate to 18 inches (Hg) vacuum Ifthe diaphragm will not hold 18 inches of vacuum (the needle drops) t . . I replace the diaphragm NOTE: Furlherinformationwillbe found in Ford Transmission Publications Vacuum Reserve Tank If a malfunction is suspected . . I disconnect vacuum supply line at the engine I plug the line I disconnect the outlet line from tank I attach vacuumtester I vacate tank to 10 inches (Hg) vacuum if the reading on the tester drops . . . I repair or replace the tank If level remains constant on tester gauge . . . I attach vacuum tester to check valve I vacate to winches (Hg) I remove plug from the supply line If reading drops . . . I replace check valve