What is the proper way to test a vacuum booster?

[GN owner]

My car has been converted to vacuum brakes over a year ago and it has not been driven since. The initial application of the brakes is hard and then starts to get easier. I am pretty sure that the vacuum booster that I got was defective. I bought a rebuilt vacuum booster minus the master cylinder and it was defective also. Does anyone know if a vacuum booster without a master cylinder attached to it supposed to hold vacuum? I've used my Mity-Vac tester on just the vacuum booster itself minus the MC and it does not hold vacuum so I counted it as defective. I ordered a vacuum booster online from Checkers and when I received it, it too did not hold vacuum and also the one they had at the store. They were Cardone rebuilt vacuum booster. Can all of these be bad or am I not testing the vacuum booster correctly?

Thank you for any advice on this topic.

 

[mhogan6]

Vacuum brake booster test:
Engine off, pump brakes 10-15 times to remove vacuum inside booster.
With foot on the brake, start engine. Brake pedal height will drop some on a good booster.

Booster won't hold vacuum without Master cylinder attached.
Check for a missing o-ring or gasket between M/C and booster.
HTH.

 

[GN owner]

Vacuum Booster

Thank you for the feedback. I guess my booster is bad since it won't hold vacuum with the MC installed. Mine does not have any o-ring or gasket so I put some RTV to seal up the MC to the booster and it still did not hold a vacuum. I'll be buying another one! Thanks for the info!

 

[cruzn57]

there is a rubber seal

between the master and the vac canister, ( black disc looking thing)
seals the canister, and the pushrod.
also check your check valve, ( white 90 degree thing hose hooks to)
it should hold vac IN the canister,
mity vac is ok, but use eng vacumn, larger quanity, and stronger !!

good luck

 

[Roger]

MityVac