Bad Brake Booster?

Daniel McCurdy

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So after replacing the other wheel bearing on my truck i took it for a test drive and discovered i had no power brakes. Pedal was hard as a rock and i had very little braking. I did push the caliper back in some but i dont think that would cause it would it? I tested the vacuum pump and right at the pump it went straight up to 21 in/hg with little to no fluttering. So then i tested it at the brake booster line and within about 1-2 seconds it went to 20 in/hg and went to 20.75 in about a few seconds. I checked the check valve and blowed and sucked both ways and its definitly working. The only thing i saw was there was a small crack in the check valve boot that goes into the brake booster. Could that small crack be the issue. Inside the cab when pressing the pedal I wouldnt call it a slow or high pitched hiss but it does make a big huff sound. At the end of the test drive i got a bit of my power brakes back but they still seem a little week. So with all that information I would think the brake booster is bad is that right?
 

Daniel McCurdy

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I didnt test that. Should i hook it up to the vacuum pump, the brake booster or both. Could i just hook up one of those handheld pumps to the booster to check it.
 

Diesilee

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There usually a capped off extra connection on the vac. block under the hood somewhere, use that.
 

Daniel McCurdy

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Couldnt get that extra cap off so instead i used a tee which went from the vacuum pump to the block with the gauge there. The results dont look good, it was bouncing between only 11-13in and when i shut the truck off it went to zero in less than 10 seconds. I made sure it wasnt a bad hose connection.
 

Isaac Ristow

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run the truck at elevated idle for 2 minuets do not touch the break pedal shut the truck off wait 5 minuets pull the vacuum check valve off the booster it needs to have a vacuum woosh when you pull it off if not definite bad booster. Boosters are around $100 I'd suggest replacing the master cylinder at the same time as they are inexpensive and when they leak out the back they cause the booster to fail often times. I put a new booster and master on my 84 this spring and man it greatly improved the brakes they are comparable to my 2013 superduty now
 

david85

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run the truck at elevated idle for 2 minuets do not touch the break pedal shut the truck off wait 5 minuets pull the vacuum check valve off the booster it needs to have a vacuum woosh when you pull it off if not definite bad booster. Boosters are around $100 I'd suggest replacing the master cylinder at the same time as they are inexpensive and when they leak out the back they cause the booster to fail often times. I put a new booster and master on my 84 this spring and man it greatly improved the brakes they are comparable to my 2013 superduty now
^^All of that.
 

Daniel McCurdy

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Ok so I did that test except I only waited about 30 seconds to pull the check valve off and there was no air at all. I actually think I can hear the air leaking out from inside the cab it seems to leak out in about 15 seconds
 

Daniel McCurdy

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Should I get a brand new ebay brake booster for only 90$ or just get a orielys rebuilt one for the same price
 

captain720

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Should I get a brand new ebay brake booster for only 90$ or just get a orielys rebuilt one for the same price
Half the parts I ever bought from o Reilly a failed out the box, but the warranty is good so if those are your choices go for the warranty at oreilys.
 

Daniel McCurdy

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Ok so I put a new booster in and things are a lot different. The pedal is pretty firm I have to press on it a good bit but I can keep pressing harder and it starts stopping faster and faster. After letting the truck sit I have about 1.5-2 pedal presses left, considering I had no presses after 20 sec with the old booster is say that's an improvement. The loud whooshing sound when I press the brakes is gone and so is the sound of it leaking when I shut it off
 

Daniel McCurdy

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The pedal taking a good bit to press could be where I put a larger master on it when I put the 2008 disk brake axle in it. I seen a lot of people say a larger master is needed so that's what I did. I believe it's the F-SuperDuty master
 

Slicknik

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@Daniel McCurdy
How much vacuum did you have once you applied the brake ? You say you changed the booster but is the vac pump still the same?

A good test is to have the truck on and apply the break for 30 seconds or more and see if the pedal falls to the floor if it does bad booster (test the new one) , if it doesn’t then you have a leak or a weak vacuum pump.
 

Daniel McCurdy

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With the new booster it does not fall to the floor. I never checked how much vacuum i had when the brakes were applied. Vacuum pump is still the same.
 

Daniel McCurdy

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With the old booster it wouldnt go to the floor but it would get harder and harder to keep the pedal down to the point it was manual brakes. With the new booster it doesnt do that anymore i can keep the pedal down and it doesnt get any harder i can even push it further and still have assist.
 

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