Hard Braking - Vacuum loss?

[jchristie]

So I'm having an intermittent issue with my brakes losing vacuum making brakes very hard to depress and stop my truck. It's a very similar feeling to depressing a gas vehicle with the engine off. Like I said, it's intermittent and sometimes it'll be weeks before this issue happens again.

I believe my vacuum pump is working fine because I was getting 22 Hg when tested. My cruise control also works. What other items run off the vacuum pump? I'm thinking it's a small leak in the hose, but why would it sometimes happen and sometimes not then? I'm going to replace the hose first. Have any of yall ran into this issue? What ways could I test if there was a leak?

Thanks in advance

 

[fsmyth]

The only other thing that uses vacuum is the climate control part of the heater/AC.
Temporarily add a cheap vacuum gauge in the cab.
If the vacuum stays up, the problem will be in the little valve in the booster.

 

[jchristie]

@fsmyth, are you referring to the check valve?

 

[fsmyth]

No. there is a valve inside the booster that meters the vacuum to the booster itself.
It is what the push-rod is seated against. And that is what is pushing the master
cylinder piston.

 

[riotwarrior]

Check valve in booster line is what I am thinking he means.

Just thinking out loud

 

[jchristie]

So I changed the check valve and no luck... Still difficult braking. There is definitely air infiltration though and my vacuum is fine. Next step would be the power booster. Fsmyth, is that valve something that's a replaceable part? Part of me is thinking about replacing the whole booster and be done with it. Is there anything else I'm missing or need to check?

 

[riotwarrior]

The valve is replaceable and is the plastic 90 the vacuum line connects to that presses into the booster.

Is the grommet in the booster in good condition not cracked and so forth?

Fire truck up rev up gently ...do not apply brakes turn off walk out unplug 90 From booster should hear whoosh of air going into booster. If not booster or grommet is leaking.

Cheap...try new grommet...then booster.

Just sayin