Just recently i replaced rusted out brake lines and just replaced my vacuum pump with a new one from accurite diesel and it feels still like the vacuum isnt working properly... The pump is strong, but the ABS light comes on and i get an initial real good, normal response from the brakes but then they really firm up before i can stop completely. Is there a chance this could be the brake booster or even the master cylinder? I really dont know what to do guys and it worries me to drive with this lingering problem and do not want to crash the truck like an idiot...

 

I think there is a check valve or something in the fitting where the vac line hooks to the booster. Maybe try replacing that fitting and if it doesn't change anything, then it could be the booster.

 

How do I test the booster?

 

I'm not really sure how you would test the booster.

 

I had the same issue.dealt with Russian roulette for 3years. I almost killed,maimed countless people before finally replacing my booster.
It was bad enough I wouldn't let my wife drive it for fear it would not stop.

 

Take the vacuum line off the booster and install a vacuum gauge to it (plug it off). Start the truck and take a reading of the vacuum. Then reconnect the booster, but leave the gauge on the system, then have someone step on the brake pedal. If the vacuum falls off and doesn't recover, I'd say it is a bad booster. If the vacuum stays the same, but the pedal gets hard, then I'd say it could be the booster OR the M/C. If you draw a strong vacuum on the system without the booster connected, at least you eliminate the pump and all the hoses.

Lousy brakes aren't something you want to fool around with in a 6,000 pound truck.

 

ok and i had replaced the booster before with an oreilly part, and now its failed again... Should i go to ford and get one from them to make sure its a quality part? and another question, is the master cylinder connected to the booster or is it the part that is down in the from rail that the brake lines to the rear exit from?

 

So you know for sure it is the booster?

The M/C is the part bolted to the booster. The thing down on the frame rail is the RABS (Rear ABS) valve. When those fail you tend to get the opposite effect as what you're describing. You step on the brake and the pedal goes soft (like the ABS is kicking in).

 

Ok do y'all think I shoul go ahead and put a new master cylinder on there too?

 

Sounds like the system wasn't bled properly.

Bleed master cylinder.
Bleed RABS, directly below the dash on the drivers side frame.
Bleed rear breaks.
Bleed RABS
Bleed front brakes.
Bleed RABS.
Bleed rear again and then bleed front.

Should have some good brakes. =)

Try that first, then if you cannot get brakes working.
Replace the master.
You'll have to bench bleed it first, which is easy. Or you can do it in the truck (messier)

Then you shouldn't have to bleed the crap out of the RABS system again, cause the oil will be in there already.

just bleed RABS till the air is out, then the normal process of working your way to the closest to the cylinder.

 

I think the master cylinder is probably fine and you just need a booster, but if you want to do them both at the same time, I think you could probably save yourself some time (if, indeed, they both end up needing to be replaced).

I still think it's probably the booster though. Did you test it like I suggested above?

 

I missread it a bit earlier, but I'd still start with the bleeding process above.

When the booster is failing due to lack of vacuum, the brake light will light up on the dash cluster letting you know low vacuum.

Brake fluid is cheaper than a vacuum booster or master cylinder and he just replaced all the lines.

 

Wait, who is this ^^ guy!? What's up William? Long time no see, man. How are things with you?

 

Thooper ****ty. =)
Thanks for asking though.

 

Ya I tested and the pressure drops off. There's sufficient vacuum but when I press the pedal while driving it gives good braking for a second and then it seems like the vac pressure isn't recovering? So I think it's a booster. But when I bled the truck, I only opened the bleeders on the axle and that was it while I had someone tap the brakes. I've never really liked bleeding brakes before bec I never seemed to be doing it right haha