im getting close to having my 50 f1 roadworthy, and my brake system has been done for sometime, however im still having issues. let me start by saying the master cylinder is new and bench-bled, brake lines are new, disc brakes in front and drum in the rear (it actually has a malibu frame stub with a firewall mounted master cylinder). the rear drums are well adjusted, though the shoes only look to have about 1/4 " of material left (which i thought would be ok for now). When the engine is running and i go to press the brakes, there is a hissing sound or burst of air coming somewhere from the brake booster that sounds fairly similar to air brakes on a semi. That by itself seems odd, but in addition, the brakes just outright ****! the pedal feels firm and it won't go to the floor which is good, but i have to REALLY push on them to get the truck stopped. i noticed that if i push the pedal, then let it come up and push it back down (usually 2-3 times in a row) it stops better and better everytime, but im just not sure how to diagnose this. a faulty brake booster perhaps? i've fiddled with my proportioning valve, bled the brakes plenty of times, I'd just like a few outside opinions if at all possible guys. thanks! edit: just for the sake of anyone with similar problems, my brake booster was bad. changed it out and now im a stopping fool! thanks hamb
If you are pumping the brakes and they stop better ,you still have air in the lines. As for the noise,,do you have your all your vacuum lines hooked up? Single or double master cylinder? What size bore is the master cylinder? HRP
I'd sure put money on a bad power brake booster, all the symptoms point to a bad diaphragm in the booster. Be sure the vacuum hose to the booster is connected to the proper carb./intake port. I don't know of any way to test the booster other than replace it and try again. BILL RINALDI
As Bill said, the booster is ruptured. The hiss you hear is the vacuum "escaping"(you know what I mean). The pedal is hard because there is no power ***ist to help apply the brakes.
Sounds like the booster is leaking. Try a stethoscope with an open tube to listen for the leak. Do the brakes feel different if you don't run the engine? The booster should hold vacuum for a couple of pumps of the pedal. Pump the pedal without the engine running then start the engine to see if you get any ***ist. A master cylinder designed for power brakes will be very hard to push without the ***ist.
Change the booster.If it sounds like air brakes on a truck when you mash the brake petal its getting plenty of va***n just leaking it out.At most parts houses it cheaper to buy the booster and master cylinder as a unit as it is to buy just the booster.
The Jalopy Journal
