Break vacum problem

[Mator]

Before I start replace parts without knowing what to start with can someone help me a break problem? I have noticed since putting everything back together that the break pedal acts like it is getting sucked in from too much vacuum. The break pedal does not come back up by itself but I can pull it up by hand. When I let go it gets sucked back in about a an inch. This causes the breaks to stay engaged until I pull it back up. I checked the one way valve at the booster and it seems okay. I pulled the vacuum hose off and plugged it and it seems to work fine as manual breaks. I do not have a lot of experience with breaks. I did have it all apart and I think I got it back where it is suppose to be. Attached are some pictures I took for reference. Thanks

[LockDoc]

Originally Posted by Mator

Before I start replace parts without knowing what to start with can someone help me a break problem? I have noticed since putting everything back together that the break pedal acts like it is getting sucked in from too much vacuum. The break pedal does not come back up by itself but I can pull it up by hand. When I let go it gets sucked back in about a an inch. This causes the breaks to stay engaged until I pull it back up. I checked the one way valve at the booster and it seems okay. I pulled the vacuum hose off and plugged it and it seems to work fine as manual breaks. I do not have a lot of experience with breaks. I did have it all apart and I think I got it back where it is suppose to be. Attached are some pictures I took for reference. Thanks

Check to make sure your pedal return spring is not missing or broken. There are a couple of pictures of where it is located in this thread....

http://67-72chevytrucks.com/vboard/s...d.php?t=110374

LockDoc

[GASoline71]

What is that gizmo attached to the power BRAKE booster vacuum line? Looks like a check valve thingy of some sort with a smaller vacuum line going to it. You need a dedicated 3/8" vacuum line going to your booster from either the carb or from the intake manifold. No "T" fittings or check valves.

Gary

[Mator]

Thanks I will start there. This is the way it came when I purchased it and reassembled it the same. I will try to reroute to a dedicated vacuum and try it again. Thanks

[hugger6933]

That type of valve was a factory type thing on lots of trucks in the 80's if remembrance serves me.

[davepl]

Just in case this helps with the return spring. But that vacuum line routing, as noted above, looks pretty wonky.

[Fitz]

Originally Posted by Mator

Before I start replace parts without knowing what to start with can someone help me a break problem? I have noticed since putting everything back together that the break pedal acts like it is getting sucked in from too much vacuum. The break pedal does not come back up by itself but I can pull it up by hand. When I let go it gets sucked back in about a an inch. This causes the breaks to stay engaged until I pull it back up. I checked the one way valve at the booster and it seems okay. I pulled the vacuum hose off and plugged it and it seems to work fine as manual breaks. I do not have a lot of experience with breaks. I did have it all apart and I think I got it back where it is suppose to be. Attached are some pictures I took for reference. Thanks

Brakes stop you, Vacuum pressure helps them do that Breaks are just bad things that have happend to useful things rendering them useless.

[Mator]

Originally Posted by Fitz

Brakes stop you, Vacuum pressure helps them do that Breaks are just bad things that have happend to useful things rendering them useless.

Now that's funny. I didn't even see that. I hope it doesn't break because I need my brakes.

[Mator]

Okay new vacuum line, eliminated a whatchamacallit and spring return was installed. Still same issue. Could the rod from booster to master need adjusted.

[Custom/Ten]

Can we see a picture of the spring you installed? Could be a gunked up compensating port but your mc looked really clean so I'd like to see the spring before we start talking about that. Btw, that gizmo looks like a bb filter, here's mine.

[Custom/Ten]

[Mator]

Originally Posted by Custom/Ten

Can we see a picture of the spring you installed? Could be a gunked up compensating port but your mc looked really clean so I'd like to see the spring before we start talking about that. Btw, that gizmo looks like a bb filter, here's mine.

I don't have a picture but spring is clean. I disassembled everything while in tear down mode. Painted and cleaned everything up then reassembled with a new master cylinder. I think everything is put back right but it still acts like its being sucked down and when I reach down to pull it back out you can feel the vacuum wanting to pull in down.
This is the pict before I tore everything down. And yes I replaced to air cleaner and working on the gas line before I get yelled at . Thanks

[AirSpeed]

Is that a second check valve installed on you brake booster vacuum line? If so its not needed, the elbow going into the brake booster is a check valve. Have you tried removing the second check valve in the vac line?

[Custom/Ten]

Re-read your posts to make sure I understand, sounds like you reassembled everything and the only thing you changed was adding a new MC. Theres only two things I know of that makes the pedal return. One is the spring on the pedal they are talking about, the other is a return spring inside the mc that pushes the piston back. If both these springs were gone gravity would pull down on the pedal activating the booster, IMO, never seen it, never heard of it, just a theory referring to a hypothetical situation. I have no idea what's going on with your brakes lol. If it is true though that the only thing you changed is the MC then that is what I would replace. I'm not going to suggest that you do because I'm not sure about it., that's just what I would do. Sounds to me like something is activating your booster with a greater force than what what your return spring can counteract.

P.S. I would advise that you not take my advice as I am ignorant as $&€@

P.S.S. Hopefully somebody will see your post and be able to help you out, but however you get this figured out please let us know what the problem is as I am super curious as to what could cause this!

[Mator]

(Sounds to me like something is activating your booster with a greater force than what what your return spring can counteract.)

That is exactly what its doing on. I just don't know what. Thanks

[swamp rat]

First thing i notice is that inline check valve appears to be reversed in the latest picture from the old picture.. take it off and see which way is closed and which way is free to pull vaccum, make sure the open side faces the intake manifold.

EDIT: Note the silvery ring around it is not centered, its offset, in the latest pic the ring is closer to the booster, in the early pic the ring is toward the intake..

I agree that on my truck there is not an inline check valve, the little plastic one that attaches to the booster is the only check valve my truck ever had, if it was me i'd pull the inline one and replace the booster one if its not working properly.

[Mator]

I removed the inline and still the same. I guess the next step is to replace the booster. Thanks

[swamp rat]

Did you check the one way valve that plugs into the booster? they can be had for about $6. Mine had a bad hardened rubber gasket, again it should allow vacuum to pull out of the booster but not go back in.

[snipescastle2]

seems to me, if the booster was bad, you would hear vacuum noises inside the cab, especially when depressing the pedal, or the pedal would be hard all the time. by chance was the master cylinder changed recently there's a chance the pushrod length may not be correct also.....
HTH,
Ben

[Mator]

Yes, it was replaced during reassembly. How can you tell if its to short?

[snipescastle2]

If you take your master cylinder loose from the booster, take a pencil or similar diameter rod, etc. and stick it in the inside bore of the master cylinder.
measure that against the length of the pushrod on your brake pedal, that should give you a pretty good comparison.
HTH,
Ben

[kwmech]

The other piece that is in question is nothing more than a filter to keep gas vapors out of the booster. GM had a thought years ago that gasoline vapors can damage the rubber diaphragm in the booster. I think it is nothing more than a carbon filter

[snipescastle2]

I'm pretty sure the rod that is inside the booster is fixed length, unlike the manual brake pedal push rods, the power brake master cylinders don't have a very deep inside bore, where as the manual brake master cylinder's do.....
in the attached picture, you'll see two red arrows, this distance, or depth will be deeper on manual brake master cylinders, or narrower for power brakes.
So, if you have a manual brake master cylinder on a power brake booster, the pedal may not have enough travel to keep the pedal in a normal position....I hope this isn't too confusing....
Ben

[snipescastle2]

I'm pretty sure the rod that is inside the booster is fixed length, unlike the manual brake pedal push rods, the power brake master cylinders don't have a very deep inside bore, where as the manual brake master cylinder's do.....
in the attached picture, you'll see two red arrows, this distance, or depth will be deeper on manual brake master cylinders, or narrower for power brakes, as in the second picture.
So, if you have a manual brake master cylinder on a power brake booster, the pedal may not have enough travel to keep the pedal in a normal position....I hope this isn't too confusing....
Ben

[Custom/Ten]

Sniper is right in my experience, however I was reading my brake textbook and saw a picture of a brake booster with an adjustable rod so they do exist. Looked like like the part of a window regulator where you attach the handle, toothed I guesse you would say. I'd show you a pic but I don't wanna post copyrighted pics. Sucks your still having trouble with this. I'm studying for my brake certification, I'll let you know if I come across anything but I've already read this book 3 times and have come across nothing I remember that could cause this.i think you have a real unique problem here that is likely due to mismatched parts which is why it's not in the textbook. Textbooks mostly assume your working on factory cars, they're not really made for hot rodding. That said if you do wanna look through a textbook the new versions are expensive but sometimes I see 10ish year old textbooks on amazon for around ten bucks. They make Hanes manuals look like dr suess books. Worst case senario you learn everything about brakes except how to fix this problem.