Vacumm boost brake system

[P Dubya]

I have and older Ford ( I think it is an F 600 or something like that) Had good brake when it was used a few months ago but now the pedal just hits the floor. Brake fluid level is fine and I opened up the bleeder on the booster (mounted low on the left frame rail) and pumped some fluid through it... No air. I seem to remeber being able to hear the booster work when the brakes worked correctly, somewhat of an exhaust sound. Now I get no sound out of it... Any ideas or pointers on what to check into?

 

[goodysgotacuda]

A bad booster will result in a rock hard pedal [with no assist], generally "going to the floor" isn't a symptom of a bad booster.

A bad master could leak into the booster and cause it to fail as well, compounding the problem. If the pedal has little-to-no resistance to it, there is a hydraulic problem in the system.

 

[ddawg16]

With the engine off, push on the brake. If the peddle goes to the floor and you don't have any leaks, replace the master cylinder.

 

[JayCrash450]

If no leaks are apparent at the wheel cylinders or Pistons than it's likely a bad master. Agreed with the poster above, a bad booster usually doesn't result in a pedal with no resistance...quite the opposite.

 

[LS6 Tommy]

A bad booster will result in a rock hard pedal [with no assist], generally "going to the floor" isn't a symptom of a bad booster.

A bad master could leak into the booster and cause it to fail as well, compounding the problem. If the pedal has little-to-no resistance to it, there is a hydraulic problem in the system.

^^^This^^^ Sounds like a "bypassing master cylinder".

Tommy

 

[brownbagg]

its proberly leaking under the carpet

 

[tcsalvage]

I learned a trick a long time ago from an old man, get three pairs of vice grips and ''lightly'' crimp off each rubber hose. Crimp them hard enough to close them not hard enough to crush them (one to each front brake and the one down to the axle for the back brakes). Now hit your brake pedal after all of them are crimped, if its hard there is nothing wrong with your master cylinder, if soft replace master cylinder. If the pedal was hard release each of the front lines (one at a time) and check the pedal pressure again, if the pedal falls away after releasing one that wheel is the problem, if not release the rear after recrimping the front and check. This has worked every time for over 35 years on every make of vehicle I have ever checked brakes on.

 

[theoldwizard1]

its proberly leaking under the carpet

Carpet ? On an old F600 ??? That's funny !!!

 

[joe_padavano]

Carpet ? On an old F600 ??? That's funny !!!

X2. First, I'm assuming this is a Hydrovac system, with the booster separate from the M/C, correct? There's a master cylinder and a separate slave cylinder bolted to the Hydrovac. Either one could be bad, causing this problem.

 

[gayler]

Does it have duel master cyl's one on the firewall feeding the one on the frame?

 

[Aeromech]

replace the MC

 

[autonaut]

I learned a trick a long time ago from an old man, get three pairs of vice grips and ''lightly'' crimp off each rubber hose. Crimp them hard enough to close them not hard enough to crush them (one to each front brake and the one down to the axle for the back brakes). Now hit your brake pedal after all of them are crimped, if its hard there is nothing wrong with your master cylinder, if soft replace master cylinder. If the pedal was hard release each of the front lines (one at a time) and check the pedal pressure again, if the pedal falls away after releasing one that wheel is the problem, if not release the rear after recrimping the front and check. This has worked every time for over 35 years on every make of vehicle I have ever checked brakes on.

Sometimes simple solutions are the best..