Brake vaccum pump seal leak

Brake peddle should be hard, if bake peddle soft check master cylinder or replce, try bleeding brake system too. Ceck if check valve is bad this is located on vacumm line from intake manafold to booter pump body. brake seal at check valve booster pump should hiss if not check vaccumm line for leaks if no leak in line replace check valve they don't cost much.

Hi, It sounds like your brake master cylinder survo is leaking causing the vacume from your engine to drop to low. You can pull the vaccum line off the survo and block the line properley then start your car and pump the brakes. DONOT DRIVE CAR with vaccum line off your brakes will be VERRY POOR.

A hissing sound when depressing the brake pedal is an indication that the booster is leaking. Another indication is that the pedal will be more difficult to push down before starting the car after it has been sitting for a while. A faulty brake booster will only make it more difficult to apply the brakes. However, it should be noted that a leak in the booster may be caused by brake fluid leaking from the master cylinder into the booster and this could become a dangerous problem.

Check the hose connections to and from the vaccum assist unit, then check the vacum assist unit for damage ( leaking/hole in seal/sucking air ).
Sincerely,

Doc Michael

The boster has hoses tho the power steering that operate it.

Hi. Power brake booster can have a big vaccum leak. does it stall in park just idling and then put on the brake. Vaccum leak is to be looked for. If you have to be driving and then brake and it stalls it may be staying in lock up.

do you see any fluid on the ground? if not...master cylinder is bad...vaccum is sucking brake fluid into the booster....is your car running poorly sometimes...if so the vaccum is also sucking it into the engine.....120$ should fix this at any brake shop

This is a problem with your fuel mixture, it is getting too much oxygen. It could be a problem with a vaccum leak, fuel filter, fuel pump, or fuel injectors.

A good way to test vaccum leaks is to: start the engine, spray carberator cleaner around the vaccum lines. if you suddenly hear a difference in the engine (RMS shoot up) then not only have you figured out if you have a vaccum leak, but you also know where it's at. Carb cleaner is basiclly a potent fuel so you'll hear the engine run stronger if sprayed directly into the vaccum line.

If you dont find that it is a vaccum line, I'd clean the fuel injectors and replace your fuel filter. If this doesn't fix your OBD problem, then it's still good to know that they are nice clean and new, neither are real expensive either.

If you dont like to keep your car full on gas, it is most likely your fuel pump. The pumps have to work harder and harder with the less and less gas you have in the tank. Also, if you have a standard tranny you are more likely for the fuel pump to go out because the revs are higher.

Let's not hope it is the Mass Airflow Sensor (MAF) because they can be costly and a pain to replace.

if you can see a good amount of wet brake fluid between the brake master cylinder and the brake booster. and you have been adding fliud often,you could have a bad master cylinder. it has to be replaced not rebuilt. you however may have a far more common problem, a rusted through brake line.have someone pump the brake pedal, than look under the car for a brake fluid leak ,repair as needed. than bleed the brakes for a good hard brake pedal
good luck chris

Ran into this problem the same way you did, but back in '75 with a Ford 289.
First of all,and you've probably done it already, is to make CERTAIN all vacuum hoses and connections, tees etc. are leak free. Then move on to diaphram actuated valves (egr valve, heater core valve, vacuum modulator valve, distributor vacuum advance.... and then there's the diaphram actuated dampers for a/c and heat in the dash) ALSO, a good idea is to add a larger than stock vacuum canister, such as a large coffee can - metal of course!