Brake Booster not enough compression

[Rick Yasenchack]

I bought my 63 2-door convertible 62 series a few years back, previous owner said a new brake booster was just installed and that was why brake pedal was a rock.  Did not know.

Just had engine reworked and I completely redid brakes.  Engine back in and running, brakes still like rock.  Mechanic only getting about 12-15psi I beleive he said.  He is not sure what to do other than add electric booster pump, going to test booster in morning

Any suggestions before summer ends in Ohio

[Russ Austin]

Make sure there is good vacuum going to the booster, and that the check valve is working. 

[Dennis P. DiBari]

Hi Rick,

     A lot of GM car owners make the mistake of having a 3/8" gas line hose from the check valve on the booster to the back of the carburetor.  Please make sure that you have/get a Certified 11/32" Vacuum Hose.  The gas hose will collapse.  When I rebuilt my entire brake system, I sent away for the Certified 11/32" vacuum hose.  Check to see what is installed.  If the brake is still hard, it will t hen be the booster.

Dennis DiBari, NY

[Russ Austin]

If the booster is an aftermarket one, they are rock hard on the pedal. I have one in my sedan and the brakes are great.  A vac pump is not necessary unless the vacuum is low. if the vac is low, then there are engine problems, not brake problems. 

[Rick Yasenchack]

I’m puzzled by your reply 🤔.  You stated aftermarket will be rock hard and same time one on your sedan and works great???

[Russ Austin]

My sedan has an aftermarket booster and master cylinder. The brake pedal is rock hard as in there is no swish in the pedal before there is braking, or another way to say it is there is no  pedal drop before I have brakes being applied. 

[Rick Yasenchack]

He is only pulling about 12-15 off the carb, was going to play with timing which needed tweaking and he thought it would improve some 

booster looks aftermarket and was new when I purchased, and always hard pedal. 

Im just about to get car back after 2 years in shop, which rebuilt engine, which didn’t have any issues other than leaks and carburetor issues.  Long nightmare 

thanks for sharing, will follow up Monday when I see him again 

[Dennis P. DiBari]

How is the vacuum hose I wrote you about?

Dennis DiBari

[Rick Yasenchack]

I will check on that Monday, the hose is new I know.  Will check size and type