Bad brakes

[Schurkey]

Yes i just bled them and the pedals soft. I think it might be the booster and master cyclinder.

Did you bleed the system with a scan tool? If not, you didn't do a thorough job.

Why suspect the booster when the problem is a low pedal?

Does the truck stop? What is the history of this? Low brake fluid level? Why were the rear cylinders changed--did they leak? Front pads worn-out? How many miles since the previous brake work?

 

[Caman96]

They go to the floor and make a pssshhh sound

This is why I suspect the booster. It could be a vacuum line or master cylinder too.

 

[Supercharged111]

This is why I suspect the booster. It could be a vacuum line or master cylinder too.

That won't make the pedal hit the floor though. In fact it would give you a rock hard pedal that takes 2 feet to stop the truck. From my perspective, whether there is more than 1 problem is irrelevant. We KNOW the pedal hits the floor, which means if there's no leak it's the master cylinder.

 

[Caman96]

That won't make the pedal hit the floor though. In fact it would give you a rock hard pedal that takes 2 feet to stop the truck. From my perspective, whether there is more than 1 problem is irrelevant. We KNOW the pedal hits the floor, which means if there's no leak it's the master cylinder.

I just went through this, same noise, and first push would go to floor. Yes, you could pump it and get pressure but first pump, it did go to floor. A new booster resolved without any bleeding.

 

[Supercharged111]

I just went through this, same noise, and first push would go to floor. Yes, you could pump it and get pressure but first pump, it did go to floor. A new booster resolved without any bleeding.

Isn't the connection solid from the pedal to the master?

 

[Caman96]

Isn't the connection solid from the pedal to the master?

You know, now that I’m recalling this, I shouldn’t have said “to the floor”, maybe it just felt that way. If you stepped on brake steady and slow, it would go down making the pssshhh noise. But your right it had pressure with a quick hard stomp. But it did seem to travel far with a slow steady pressure on pedal. A new booster did resolve it.

 

[Schurkey]

If the pedal travel is excessive, a GOOD booster will "pssshhhh".

Diagnose and repair the pedal travel, I bet the booster "fixes itself". Given that the brake hydraulic system has been opened up, and almost-certainly NOT properly bled, I'd be suspecting air in the system before suspecting a failed booster. A failed master cylinder is a strong possibility.

I have had failed vacuum brake boosters on both of my Luminas; but they're known for (infamous for) having low power assist (poor braking power) needing both feet on the pedal and a big squirt of adrenaline to get the car stopped--while having no other signs of a failed booster.

 

[Erik the Awful]

A bad booster won't cause the brake pedal to go to the floor. A bad master cylinder will.

 

[Marcelo]

Probably master cylinder, booster may be going out too. Did you bleed the system after changing the wheel cylinders? Air in the brake hydraulic system will present these symptoms. But this sounds like what my Burb did before the master cylinder was replaced.

Forgot to say that my rpms move when i press the brake. Searched it up and a bad booster can cause that too.

 

[HotWheelsBurban]

Forgot to say that my rpms move when i press the brake. Searched it up and a bad booster can cause that too.

Yes the half ton gas trucks are vacuum boosted and that can be affected by the engine, or affect the engine rpms as you've noticed.