Need expert brake help

[nutz]

as soon as you start it you should feel the peddle stick/get softer
if you pull the check valve off the booster do you have suction
could your check valve be bad or in backwards
just some thoughts

[nutz]

just looked at the pick check valve is in correct
that looks like a dual camber booster ,i would think your problem is there
if you pull the check valve out of the booster when running engine should stall

[Drummerdad]

Yep, pulling the check valve causes the engine to die. I borrowed a vacuum gauge from a friend, and it pulls about 15" of vacuum (mercury) at idle, which is about 800 rpm. The gauge says its timing, but Im not really sure about that. I set it at about 8-9 degrees, which is what I had read I needed to start it at. Ill adjust it this weekend, and see if I can get it higher. That might explain the off idle stumble, and hopefully that will go away. But I havent messed with any adjustments on the carb.

I dont think thats the problem though, because when I rev the engine, the vacuum goes into the green, or about 18-20" of vacuum where it should be. But the brakes dont work any better when the truck is going at speed. If it was inadequate vacuum, it would be weak at idle, then get better when I rev the engine or drive, and work as it should. But its like the booster isnt even there.

I might try to pull a vacuum on the booster itself and see if it has a leak.

[PwrWgnDrvr]

Disconnect the vacuum line from the booster, plug it, then drive it and see if there is a difference. If not, the booster isn't working

[nutz]

some boosters .. if it holding vacuum the push rod might be adjustable
might not have enough travel
if your getting 18" of vacuum it should be plenty for at least one good stop

[BigBlockTrucks]

If the booster and the check valve are working properly,you should be able to start it and turn it off. Then come back hours later pull the line after the check valve. The booster will still be holding vacuum.

[Drummerdad]

So I worked on it a little today. I got the timing set to 10 degrees, and the vacuum at idle went to about 17-ish inches. I would have to go to probably 11 or 12 degrees to get 18 inches of vacuum. The brakes are not really any better, even if I rev the engine a bit or drive it, which would increases the vacuum well into the green range on the gauge. Still a very firm pedal, and not enough braking. Im thinking the booster either isnt big enough, or the master cylinder is the wrong size.

For those who didnt follow the build thread, when I started to make the truck drivable, it had next to no brakes. I had to have a friend come over, and we worked on it for awhile. He figured out the rod between the master and the booster diaphram was too short, so I made a new one. I might try looking at that. Take the master cylinder off, and push the pedal to see if the rod moves. I dont know if that will work, but Im convinced the booster just isnt working.

[Drummerdad]

So I dug into the brakes today, and figured out the issue. I have been a victim of getting what I paid for. Time and time again I learn the hard lesson of buying cheap parts from vendors who dont care about you, your project or your safety.

So, the master cylinder has a casting number of 227161, making it a 1" bore MC for a 64-73 mustang, and it says it is good for disc/drum setups. The booster is a mystery. I bought these as a set from Pirate Jack, specifically for a 67 dodge d100, allegedly. Remember the rod that goes between them was too short, and never would have worked. I had removed the MC and the booster from the truck, and had them on the table. I noticed there was no gasket between them, and the mounting flange had surface rust on it, meaning it was not sealed. As I was reading up on it, a person asked if there was a gasket between the MC and the booster, and I found a that post said "No, the MC is sealed and the booster is sealed, if either of them leaks replace them." Then it dawned on me, the booster is under vacuum, and the MC is under pressure, they have to be separated from each other. That seems simple, but if the seal on the booster wasnt holding its vacuum, then the vacuum would come right out. Also there is a chance, if its sealed there, that the vacuum could draw fluid through the back of the MC, and ruin the booster, which I have had happen on a car before.

So, I flipped the booster over, and pushed on the brake pedal rod, and the seal just pushed out. Its made to be held in place by the MC. but I noticed there is a depth difference between them that wont alow that to happen. The flange on the MC is 9/16" deep, but the booster has a hole depth of 31/32" without the gasket. If my basic math hasnt left me, thats a difference of 13/32". So, I stacked a few large o-rings and a grommet in between them and put it all back together for a test, and it worked. I know this is not a permanent fix, but its working pretty good. Ill have to make a spacer to hold the gasket in place, or buy another booster.

I cant count how many times buying a cheap part has cost me more than I paid for it. Im going to just start ignoring the first 3 pages of a google search, and maybe the Pirate Jacks and the Uncle Jimmys wont be on the 4th page, and I can start to get some good parts. You expect it from Rock Auto, but now everyone is selling cheap garbage.

[nutz]

something doesn't seem right
that push rod just pulled out ... is that the part that wasn't long enough
thought you where talking the other side of the booster
thought that one was attached to the diapham
looks like your onto something
does it work now

[Drummerdad]

It does work. It actually feels spongy now, because there is air in the system. But I can drive it, and pump the brakes and they get better. I didnt have that before. I can actually feel the booster working. The rod (which is the one I had to make) is threaded in, but that seal or rubber gasket just falls out. I think Im going to make a spacer that goes between the master and the booster to hold that gasket in place. Right now its just a few large o-rings and a grommet, so it works but it can be better.

[nutz]

sweet glad your getting there