Brake hissing sound

Hi all -

My 1998 manual 4x4 Tacoma suddenly started making an air hissing sound when I press the brake pedal. Braking got worse when it started - which makes sense. I just assumed it was the brake booster. So, I replaced it and got the same symptoms. I thought maybe I got a bad new booster, so I put in an another new one. Same symptoms.

I guess at this point it can only be the master brake cylinder or a vacuum leak. The funny thing is, my master brake cylinder is not leaking brake fluid.

Any ideas what is going on?

 

The vacuum hose tht comes out from booster

 

Thanks for the reply. Are you talking about this hose? My hose was still good. Replaced it anyway. Still have the same problem.

 

The hose goes to that silver valve on the booster
Assuming that valve new/came with new booster?

 

Has to be V leak

Can u get a buddy to start taco and press brake while you’re under hood listening?

if you hear something
Can confirm that area with soapy water spray or windex for exact loose hose

 

More than likley the vaccum diaphragm.

 

In both new boosters? What are the odds?

 

New = Never Ever Worked. Too many times you diagnose an issue and put a new part in and it doesnt fix the problem, so you go down a rabbit hole diagnosis only to discover that the new part is bad also.

I have a buddy that is a Ford Dealer, Master diesel tech, he oversee's 3 apprentice techs. Brand new 6.7 going into a 2022 F350. They start it after the install and it has a hard miss. It also had a cadence in the cranking like there is bad compression. Power Balance shows a low cylinder. What they found is that when they pressed the camshafts together, they are hollow and oil runs throught them, the factory assembled the intake cam wrong. With these trucks you have to take the cab off to access the motor for major repairs.

 

Can start the car with foot on brake pedal and the vacuum should pull the pedal down lower enough to feel.

 

Well - vacuum off the engine is good.

 

Can pull a vacuum on the booster (at the other side of the hose going into the booster from the engine) and see if the vaccum holds.