Odd power brake problem

[77sport]

I just finished installing a power brake conversion and am having a strange problem. Everything works fine till I start the engine and vacum is applied to the booster. Then when the pedal is pushed down it does not come back up when you take your foot off the pedal, it stays down about half way and you have to pull it back up by hand. With the engine off and the vacum bleed off the pedal will always come right back up no matter how hard you put on the brakes. I have never seen a booster do this before and it has me stumped. Anyone have any ideas what may be causing this? Do you think it may be a defective booster? system has normal vacum and the check valve is working ok and everything is plumbed correctly.

 

[broncnaz]

Sounds like a defective booster they may have left out a return spring when they built it or its a weak spring. Is the pushrod coming out of the booster to the MC adjusted right if its not out far enough maybe the booster is taking up the slack and sticking down. I barely have to step on my pedal it only goes down about a 1" -1 1/2" for full brake pressure

 

[77sport]

its adjusted right , with the engine off(no vacum) the pedal only goes down a couple inches and is very solid, and you can really feel the spring push back hard, and it comes right back up. the problem is with vacum applied the pedal will not return. is there a seperate spring in the booster? I had read an eariler thread where the rod from the booster to the master cyl was not adjusted right and this caused the brakes to not release all the way, might this be a related problem?

 

[broncnaz]

could be but if its adjusted right then there shouldn't be a problem there is a spring inside the booster housing but if its pushing back with the engine off then it should be ok Try this engine off push on the brakes start engine you should feel pedal go down a little if not Id say bad booster. who's conversion do you have? my other Idea is that it may be a faulty check valve a new check valve is only a couple of bucks at the local parts store I'd try that

 

[77sport]

i did check the ckeck valve and it seems to be working ok, the pedal goes down with the engine started and the booster is adding braking force the pedal just wont come back up, if i shut the engine off and pump the brakes 3 or 4 times to bleed of the vacum stored in the booster the pedal will start coming back up once the vac is gone. like i said i have never seen a booster do this before.

 

[chuck]

Sounds like the pedal assemble has a drag. The pedal should be very free and have a little free play at the top. I had a guy come in with the same problem. He would push the clutch then hit the brakes and the brake pedal would not come back up. We pulled the rod that holds the pedals in place and cleaned it and all was well. It only takes a light drag to cause the pedal to stay down even with only one pedal. Remove the brake rod and the pedal should be very free. If it is check the bell crank to be sure it is also free. If this is one of my P/B brackets there is Oilite bushings (self lubing) in the bell crank so if it is not free there may be a bind if that is the case hit the bell crank bolt with a hammer if it still does not free up loosen the bell crank bolt 1/4 turn.

 

[ET]

I had the same problem that you have and what chuck said fixed the problem. The bell crank bolt was too tight causing the bind. I, being a dumb ass, tighten it. Once I loosen the bolt, pedal came back up. I had to play around with the tightness of that bolt so the nut wouldn't come loose and still allow movement. Good luck.

Eugene

 

[bpatton74]

Get the nut where you need it for no drag and use locktite to keep it there.

 

[chuck]

The nut is a nylok, it will not come loose, even if there is a gap between the nut and washer. That is why I pay almost a buch for that nut. Guess I need a little sticker. Also even if the nut fell off the bolt is too long to come out but would make the brake pedal move more.

 

[77sport]

I discovered that the bellcrank was the problem and have corrected it , brakes are now working corectly.