This Ford truck still sucks!!!

[jgr1974]

OK,

What do I need to do now? I replaced the check valve and rubber grommet after the hissing sound started. Started the truck up, and the hissing sound is the same. where is the leak now?

Jeremy

 

[Captain Ledd]

Grr.. trying this again without my browser being stupid...

Based on a search for previous posts. It does point to a vacuum leak in the brake booster area. However low vacuum in general can case brakes to get hard and not work as well. Also IIRC, boosters are just a rubber diaphragm and as such can pop.

Does it idle high as well?

Things to do:

Acquire a Vacuum Gage. Though it's probably not exactly a necessity in this case, it's a handy thing to have. This will let you know if the vacuum is indeed low and is not some other problem. It should read 18-22 inches or so at idle.

Find all the vacuum line connections and anywhere there is vacuum going (including the booster). Spray the connections and areas with starter ether while the engine is running (taking due care not to hose the exhaust manifold down). If there is a leak, the engine should rev up a little bit. And there is the trouble area. There may also be more than one if the other grommets and hoses are bad, so keep checking. I believe hosing the booster down itself around it's seam should work.

Between those 2 things you should be able to nail down exactly where leaks are and the gage will let you know you've found them all afterwards.

Good hunting!

 

[jgr1974]

more help?

Ok,

will do. If booster needs replaced how do I drain and fill system?

Also, if booster not problem I do smell a little gasoline on the vacuum brake hose leading to the engine. Should the fluid be changed?

 

[AllanD]

There is no fluid in the booster, the booster can be replaced without disconnecting the master cylinder or the hydraulic lines.

The way a vacuum assist brake power booster works is that there is
engine vacuum on BOTH sides of the diaphram.

When you press on the pedal air is allowed into the backside of
the diaphram and it's actually the atmosphere that helps you
press the pedal.

an audible hissing sound is probably a leak on the pedal pushrod side
of the diaphram.

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