How much Vacuum?

[STSFCTN67]

What is the minimum amount of vacuum for a stock 67 booster require.

My pedal has always seemed spongy and my brake light come on too late. The brakes haver been bled and everything is new.

The best I can do on vacuum is 15 and I am not sure where the timing is right now.

 

[mrmustangman357]

15 usually is enough. if the pedal is spongy you may need to bleed the brakes or swap the master cylinder. a power brake booster won't appear "spongy"

 

[67GTFB]

don't know what the minimum required vacuum should be, but 15 psi is a normal good engine reading and the booster should function well with that .... "spongey" to me always indicated air in the lines some palce or a defective booster .... the booster in mine doesn't provide the same feel as modern power disks .... so perhaps it is a relative thing .... do the brakes work well?? .... I replaced all of the lines and rebuilt the calipers with staniless pistons (from SSBC) and cleaned-up the booster air vent .... they operate smooth now but are touchy - very little pedal effort required to throw you into the w/s .... don't know if this helps ....

 

[S-Car-Go]

I have no problems with 13" of vacuum at idle and P/B. You should be fine. Prolly air in the lines.

 

[2nd Mustang]

My 67 has 12 inches of vacuum at idle due to the cam, but is enough to run the power booster. If you have those Kelsey Hayes type four piston calipers the brakes will be touchy and grabby.

 

[Rusty67]

Try this to diagnose:
With the car OFF, depress and release the brake pedal several times to releave any pressure left in the booster. Let the car sit for an hour or so. Come back to the car and feel the brake pedal. Does it still feel spongy ? If it feels spongy like you were talking about it is not the brake booster.

I would tend to agree with what everyone has said. Any time the hydrolic system is opened, except just opening the cap to fill the fuild, the system needs to be bled out. If you did work on it, which I can assume you did because you say that everything is new, then you need to bleed the system out.

 

[STSFCTN67]

figured it out

The rear drums needed to be adjusted.

 

[2nd Mustang]

The rear drums needed to be adjusted.

Being cheap, always check the little things first.