bondoboy

Is there any way to test a brake booster with a mityvac pump? I did the test where you pump the brake then start the engine to see if the pedal drops. The pedal did go down, but slowly and the brakes have a hard feel to them. I am suspecting a vacuum leak. When I shut off the engine, sometimes I hear a leak for a few seconds from the booster area. Thanks for the help.

dannyman

Brake booster leak is normally noticed during brake pedal application. If you hear a leak on shutdown it may be from a source other than your brake booster.

bondoboy

Thanks a lot. I suspect a booster problem because I don't notice much power assist compared to other vehicles, but I have never owned one of these cars before.

69elky

It looks like that you have completed the basic test for the booster.Engine off,press pedal several times to eliminate vacuum from the power side.hold pedal down with light pressure 15/20 lbs.Start your engine and see if the pedal drops slightly and less pressure is required to hold the pedal down when engine is running.If your booster is not operating and your pedal is very hard,disconnect the vacuum hose from the booster check valve and and check your vacuum,start your engine and connect a vacuum gage to the hose,at least it should be 18"to the booster.If it is lower it should give you a hard pedal.(Just a note here,camming an engine with a strong cam can cause a lower vacuum at idle.)Try and bring your vacuum in by tuning your engine,This is where in some cases you may need a vacuum cannister to hold your vacuum supply up.I think that anything lower then 16"is the rule of thumb.If you have 18" or more,see if your check valve is working properly,with the supply hose to your check valve on the booster disconnected,attach a short hose to the check valve and blow into the check valve.If you can't blow thru the check valve it should be good,if air can pass thru it is it is bad and needs to be replaced.If your booster is working and you have a hard pedal you may have a problem with your combination valve and it may be tripped closing off the front or rear brake fluid supply,crack a bleeder and see if fluid is present,front first then rear.See where there is flow,no flow valve is tripped in that direction.This can cause a very hard brake pedal feel.If this is the case you will have to reset your comination valve.I had some problems with my other car when I installed a powerbooster and in the kit this information was obtained and I used it to troubleshoot my problem for the booster,I installed a cannister from Comp Cams.My problem was camming and overlap at idle causing a lower vacuum.I hope that this little information may help you narrow down your problem.In my case I had to add a vacuum canister and this was my problem,but I did a conversion.Sometimes a vacuum pump is needed Later and save the wave Geno

77 Vette Girl

Do all basic checks as noted in above comments. Once you are satisfied the amount of vacuum and check valve are normal, then start engine run for a minute then turn off the engine.... wait 10 minutes and then quickly pull the check valve out of the rubber grommet in the booster with the vacuum hose still attached. If you do not hear the sucking sound of air rushing in the booster diaphragm..... bad booster. A good working booster will hold vacuum for days, a leaking one will hold only a few minutes.

bondoboy

Thanks for the help. I will try your suggestions. I know I am not making much vacuum at idle. I get a little over 14 inches at idle. The motor is fresh, but the bigger cam makes the idle vacuum low.