Should the brake booster hold vacuum?

[btolenti]

Another one for you guys. I am trying to test my power booster to see if it has a leak. I am drawing a vacuum on it, but can only get it a bit less than 15inHG... Then if I let it sit, it will slowly bleed off to zero.

I then get into the truck and get about 1.5 power assisted operations.

I have had, for a while now, pretty weak brakes. I have to push down quite a bit to get the truck to stop. It will lock up the brakes, but it feels like it takes more pedal travel than it should. Plus, I am trying to chase down a possible vacuum leak that may be causing me to fail emissions...

Should the booster hold a steady vacuum?

 

[NEK5]

Another one for you guys. I am trying to test my power booster to see if it has a leak. I am drawing a vacuum on it, but can only get it a bit less than 15inHG... Then if I let it sit, it will slowly bleed off to zero.

I then get into the truck and get about 1.5 power assisted operations.

I have had, for a while now, pretty weak brakes. I have to push down quite a bit to get the truck to stop. It will lock up the brakes, but it feels like it takes more pedal travel than it should. Plus, I am trying to chase down a possible vacuum leak that may be causing me to fail emissions...

Should the booster hold a steady vacuum?

I was told that it should hold a vaccum. If you run the truck for a minute or so, then kill it, you "should" get around 2 power assisted operation...

 

[JEBSR]

I have had, for a while now, pretty weak brakes. I have to push down quite a bit to get the truck to stop. It will lock up the brakes, but it feels like it takes more pedal travel than it should.

If the grommet that the 90* fitting to the vacume line is still plyable and not dryrotted then it should hold vacume. If it doesn't hold at all then the diaphram is probably leaking.
However that shouldn't cause the peddle to go down to far, it should make the brakes very hard to apply (little to no assist). If it has to sit for a while before you loose vacume then I doubt that is your problem. Might want to pull the system down and check your rear brake adjustment (if applicable) and make sure nothing is leaking and letting air into the system.

 

[ryoken]

http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm#testbooster

 

[garlicbreath]

That 90 degree fitting on the booster is a one way valve.
Do your vacuum test with it on and then pull it off to see if the booster holds. You should hear the hiss if it does. But they really were not designed to hold vacuum for very long, just long enough for an emergency stop if the motor dies.