Brake Vacumm

[tbrown5079]

I installed a complete brake booster, pedal, master cylinder etc. from a well known supplier. Nice kit and perfect for my application. 56 Pickup, stock 4.8, disc/drum, GM F body front end. Only problem is, it stops, but I can never really set it down if I want too. If I brake hard 3 or 4 times it works better, but if I don't use the brakes again for a while I get a hard pedal and it will stop, but not as quickly as I would like. They exchanged the booster because they said it was bad, but the new one isn't any better. I have 20" of vacuum at idle and replaced the booster check valve. The brake pedal travel is all good. I am going to check vacuum when running next. The fact that it is not consistent is puzzling. These engines should have more than 18" of vacuum when running right. The kit has a lifetime warranty. Any suggestions? Tbrown

[ls1nova71]

If it's one of those small dual diaphragm boosters then that's most likely your problem, they just dont work that well. When I built my street rod I used one and like yours, it would stop, but in a panic stop situation, not as well as it should. After talking with other people who built street rods I found out it's a pretty common problem. Most people just live with it but I switched to a hydro boost because there wasn't enough room under the floor for a full size booster. It works like a real car now.

[Gregski]

18" of vacuum is more than plenty to drive the brake booster, have you checked out your proportioning valve? is your rear end from a F body as well? you do say disc/drum so are your drums working as well as they should in the rear, properly adjusted they do contribute? but my money is still on that proportioning valve or what ever other name it goes by

I am building a '54 with a Camaro subframe and will drop an LS in it next year, would love to see your build.

[tbrown5079]

Thank you both for taking the time to reply. I am going to contact the supplier and see if I can do an upgrade on the booster, but with all the more weight I have that should handle it ok. Something is not quite right and the proportioning valve would be the next thing to change out. The rear end is from a 71 Chevelle and those brakes are working ok. When I get the brakes pumped up to set it down, I can actually lock them up.
The link is on here for my build site so check it out and see if you have any questions. I am very pleased with how it performs but there is a big difference between building something to drive to a car show or cruise and having something to drive anywhere anytime. I had a lot of excellent help with it and will be very happy once I solve the brake issue. Thanks again. Tbrown