Hey guys, So ive been currently faced with a brake issue for the past couple weeks and ive been debating either taking it to JCrover or doing it myself, The problem with doing it myself is i don't know if its the Master Cylinder or if its the Brake vacuum booster.

Not driving, Truck completely off:
I press the brakes and they go all the way to the floor and you can hear a whooshing sound like air bypassing something.

Driving:
Getting to the floor and you start to get about... 40% maybe 50% of your braking power but gets all the way to the floor at about tops 50% of braking power, Sometimes very rarely my ABS fights back, My brake light is flicking on and off but that did that before the brake problem.

Visual Inspection of master cylinder and Vacuum booster doesnt show any leaks or broken or loose connections.

I'm at a loss and this is kinda my last resort before just calling Jeff and dropping it off on friday, Is there any for sure way to pinpoint the problem without hooking it up to an expensive scanner or buying all new parts?!

Thanks guys ahead of time!

 

Jon,
You do realize I am a mechanic, right?
I can help if you want me to. I live in Littleton.

Why have you not been on Front Range?

 

Hey man, Ive just been busy being sick and trying to get an upperhand on all these mechanical problems, I just finished the U-joints, Fuel filter, replaced a bunch of fuses, Recharged my AC, And did my oil. I still have to figure out these Brakes, Ive already scheduled with JC for that. I would just love to know exactly what is wrong with them, If i knew it was for sure the Master then id just order one up and install it myself with my dad. But thats the thing, I dont want to order a 180 dollar part if i dont need it. Is there anyway you could tell me what it is for cheaper then 92.50. That would be really Awesome and a huge help!

 

Are you losing brake fluid or level stays the same? If you lose fluid there is a leak somewhere, you won't necessarily have to replace the MC or the booster. Otherwise my guess would be the MC.

 

No fluids lost. Stays at the same level throughout a day of driving.

 

Air pockets are really hard to get out of these systems. Possible you got one of those. A good test of the master cylinder is to jack up one side of the vehicle so both tires are off the ground. Have someone step and hold onto the brake pedal and try spinning the wheels. If they move then you have no brake pressure.

It is important to get front and rear off the ground. Brakes have 2 seperate circuits in case of failure of one or the other. Some are criss cross and some are front rear.

As for your brake booster possibly being bad ie the whoosh you hear when you step on the pedal. Again have someone press on the pedal and listen. Generally when the booster fails you get a really stiff pedal and almost no braking power. I cannot remember is yours manual or automatic?

I remember trying over and over with a brake bleeder to get the air out of my right front caliper. Only thing that worked was opening the bleeder valve and just letting it drip for about 30 minutes. Has worked perfect ever since.

 

So i replaced the master cylinder, and it turns out that wasnt the problem. Still have no brakes, My next part is going to be a Brake Booster, I cant wait to just have brakes. At least i got my oil, U-Joints, Fuel filter and AC recharged yesterday She is running excellent! Unfortunately my oil leaks are getting bad, I only had 5Qts in the engine. Sounds like i need to fix my Oil cooler lines and rear main seal... CRAP.

 

Did you try to bleed the brakes?

 

A faulty brake booster wouldn't let the pedal go to the floor. It would take away the power assist and give a really firm,almost non-functioning pedal.

Did you happen to bench-bleed the MC before installing it? I'm betting you either have A: air in the system or B: a ready-to-break flexible hose(or two)

Have someone press and hold the brakes while you look at all the rubber lines looking for bulges

 

Sounds like air in system to me. Also if you have the original rubber lines, you will get much better braking with the stainless steel (aircraft type) brake lines as they do not expand like the rubber and you get improved pressure to the brakes with no expansion of the lines.