booster question

[68_stanger]

in my 68 mustang coupe I think the power brake booster went bad and just want to make sure before I spend a couple hundred bucks on a new one. when I hook a vaccum pump to the inlet and pump it it won't hold a thing, I should think that they should hold atleast like 15Hg or so. Am I right in my thinking? Thanks

 

[2nd Mustang]

Another test is to start your engine, if your booster went south, the brake pedal should feel hard as a rock due to no booster help.

 

[68_stanger]

it acts like its working, well kinda, but it hisses when you step on the brake pedel, and the car doesn't like to stop well.

 

[2nd Mustang]

Sounds like it could be the check valve at the end of the vacuum line on the booster. I thought of that on my booster, but couldn't find a check valve to fit. Not knowing how old everything was, I went the total replacement route, booster, master cylinder, calipers, pads, front brake rubber lines, rebuild rear cylinders, new shoes. Going fast is great, but I like to stop too.

 

[HHStang]

this could also just be the lines needing bled or a bad caliper/rotor. I've spent hours and hours bleeding brakes tracking down air leaks. Try getting a set of vice grips, wrapping a rag around them to protect what you are grabbing and clamping the soft (rubber) lines feeding each wheel cylinder/caliper and pushing brake pedal and seeing if it gets better. If it does, that could indicate either air in the line at that wheel or a bad cylinder/caliper. If that doesn't work, try clamping 2 wheels at a time, etc. I have never had a booster go bad in my life by the way. By chance, did you just put Granada discs on? If so, try unbolting calipers from car, putting board or something to keep pads spread and holding bleeder at perfect verticle position and rebleeding. Good luck!