# Brake Booster/Vacuum Line Issues, 67 Tempest



## DanT (Jun 29, 2013)

Hello, I am having issues trying to find out if my brake booster is bad or not. The car sat for eight years and I am now at a point where I can work on Her. The car has a 6.6L 400 in it. The engine runs fine but when running the brake pedal goes right to the floor, and when off the pedal is rock solid. I ran through a booster test as follows,

1) With the engine off, depress brake pedal several times; then, depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line, or caliper is bad.

_Passed, pedal is solid with not sinking at all._

2) Start engine with pedal depressed. IF the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or check valve is faulty.

_Passed, pedal sank slightly after engine was started. But if pumped the pedal dropped to the floor(not sure if this means the booster is bad or not)._

Leak Test:
1) Depress the brake pedal with the engine running, then stop the engine. If the pedal height does not vary, while depressed for 30 seconds, the vacuum booster is fine. If the pedal rises, the booster is faulty.
_
Passed, pedal did not rise at all. The pedal was all the way to the floor. I pumped the brakes and they returned to solid/stiff pedal after two pumps._ 

2) With the engine off, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.

_Failed. Pedal height did not vary._

Check Valve Test
1) Disconnect brake booster vacuum hose at booster.

2) Start engine and let idle. Vacuum should be available -- if not, the check valve is not working correctly. Replace the check valve and retest.

Ok. The engine wont run with the vacuum line disconnected. I had to reattach the line, start the engine, then remove the line and there is strong vacuum. If I place my thumb over the end of the hose the engine runs fine, if the line is left open the engine dies. 

With the above information I would really appreciate some assistance. 

Thanks in advance, Dan.:cheers


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## geeteeohguy (Feb 2, 2008)

Stick a bolt in the booster line to plug it and see if your pedal still drops. Normally, a bad booster will leak vacuum, and cause rough running and stall out at idle. The symptoms you describe sound to me like the master cylinder is bad, and is leaking internally past the piston seal. This is called 'bypassing', and is fairly common. Also, take note that cars that sit lose their brakes. You very well could have corrosion/rust/leakage issues in the wheel cylinders or brake calipers, if so equipped. I would pull the wheels and and drums and inspect the wheel cylinders.


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## DanT (Jun 29, 2013)

I changed the brake booster and I am going to change out the master this weekend. I checked inside the wheels and there was no leakage. There was also no brake fluid between the master and the brake booster. I have gone through as much brake line as I can find and there are no leaks anywhere. I have seriously bled the brakes and they are fine, until I turn on the motor.:willy: With this being my first project, I am unsure how to proceed. I don't want to toss money at the problem. I figured that a new master and booster was a good investment no matter what. I was also thinking that it might be the brake distribution or proportioning valve. But again, no leaks. I had a friend suggest a vacuum leak. I'm going to test this when I get the master in and if the problem persists. I am going to drain the drake system and start over with new fluid. I suspect that the fluid is very old anyway.


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## DanT (Jun 29, 2013)

Found the leak today. When I removed the old Master Cylinder from the new booster I found leakage. So I am assuming that this means that the master cylinder is bad. I checked the best I could and it seems that no fluid made it to into the booster. I really hope this fixes the issue so I can move on to the best part of owning a Muscle Car, driving the damn thing!


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## jmt455 (Mar 26, 2012)

I think you had more than one problem.
I think the check valve might also have been bad.
Did you replace it when you replaced the booster?


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## DanT (Jun 29, 2013)

A new check valve came with the new booster. 

I put the new master on the car yesterday. Bench bled the air out of the master before I installed it as well. Still has the same problem, just not as bad. 

Now there is another issue that showed up while bleeding the brakes. The left side bleeds fine but the right side just dribbles out. I got the air out eventually but the right side does not squirt the fluid out, so I am thinking that the proportioning valve is gunked up and/or the distribution block is full of junk. Is there a way of cleaning the proportioning valve and distribution block? I have pretty much spent as much as I can for the next couple of weeks on this car. I will order the new one from NPD later.

In order to solve this I guess I have to trace every line in the car and see where there might be a leak. Then take the drum apart completely and look inside them to check there as well. The pedal feels much better but still not where it should be. I think it might be sucking in air. Way to much air was in the right rear.


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