no brakes pressure when start engine

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Jaskim06

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I'm stumped buddy, maybe time for a mechanic to diagnose this. Good luck.
Idk. Its hard to help with stuff like this from a phone. Thats all I can think of. Gotta be a a component not working with vaccum and power when cars running. I'll keep trying to figure out a solution. Sorry can't be more help.
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Mrmerc49

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Bad booster or check valve at booster or rubber hose has crack in it. Happened to me on my corvette. If you bled the right rear, then left rear, then right front, then left front and bench bled master tilted at the same angle as installed in car. I would start car and listen under dash for a hiss from vacuum leak too as these cars have a lot of vacuum powered accessories.
 

Jaskim06

Active member
207
98
28
Bad booster or check valve at booster or rubber hose has crack in it. Happened to me on my corvette. If you bled the right rear, then left rear, then right front, then left front and bench bled master tilted at the same angle as installed in car. I would start car and listen under dash for a hiss from vacuum leak too as these cars have a lot of vacuum powered accessories.
That was my problem. It was more of a crack in the hose and I looked and looked and swapped known good parts and finally plugged it off and put air to it while in soapy water and I found a crack. Hose was supple, not dry rotted or etc.
 

klear52

New member
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Bad booster or check valve at booster or rubber hose has crack in it. Happened to me on my corvette. If you bled the right rear, then left rear, then right front, then left front and bench bled master tilted at the same angle as installed in car. I would start car and listen under dash for a hiss from vacuum leak too as these cars have a lot of vacuum powered accessories.
i bypassed everything and hooked straight to the motor .. same problem .. brand new hoses after it running ,,, wheni unplugg from the boosster it sucks air real quick .. like a small vaccum suck .. psssssh
 

klear52

New member
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Idk. Its hard to help with stuff like this from a phone. Thats all I can think of. Gotta be a a component not working with vaccum and power when cars running. I'll keep trying to figure out a solution. Sorry can't be more help.
thanks for all the help ... im wondering if a valve is stuck in the abs ????
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TC_Owner_GA

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You said that when you clamped the vacuum hose shut(going to the brake booster), with the engine running, that your pedal becomes hard again, right? If you can clamp the vacuum hose shut, with the engine running, and your pedal returns, then I doubt it is an issue with the ABS.

I can't help but think that a check valve is sticking open on(or inside) the booster. Does your booster have the built in check valve on the front where the hose connects? Or do you have an inline check valve that is located somewhere on the hose itself? A brake booster has 2 different check valves that it uses to manage the vacuum assist function. One is internal and cannot be seen. The other is located on the front of the booster, or is somewhere inline on the vacuum hose coming from the engine.

Edited to add: When you replaced the booster, did you make sure to adjust the length of the rod?
 
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klear52

New member
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You said that when you clamped the vacuum hose shut(going to the brake booster), with the engine running, that your pedal becomes hard again, right? If you can clamp the vacuum hose shut, with the engine running, and your pedal returns, then I doubt it is an issue with the ABS.

I can't help but think that a check valve is sticking open on(or inside) the booster. Does your booster have the built in check valve on the front where the hose connects? Or do you have an inline check valve that is located somewhere on the hose itself? A brake booster has 2 different check valves that it uses to manage the vacuum assist function. One is internal and cannot be seen. The other is located on the front of the booster, or is somewhere inline on the vacuum hose coming from the engine.

Edited to add: When you replaced the booster, did you make sure to adjust the length of the rod?
i dont have a check valve .. but yes i put the length the correct length
 

Mrmerc49

New member
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I still think your booster is bad,the booster has a rubber diaphragm in the center. Vacuum is on both sides at around 18 to 20 in. Vacuum. When you step on the pedal which is attached to the interior side of the booster there is a bleed valve that allows air in which also allows vacuum to help the pushrod go towards the master which makes it easy to apply hence power brakes. If your booster is ripped or the internal or external check valves and bleed holes arent working it can cause all kinds of problems. Just hooking it up to straight engine vacuum wont work because it needs to be at the right inches of vacuum. Too much and the pedal will go to the floor, not enough and the pedal will be hard. If you get no air at the bleeders and the brakes are working with out the booster working then I'd bet thats the problem. Dont know how many miles are on the car. You could always call a performance brake parts company and ask for tech help.
 

Jaskim06

Active member
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I still think your booster is bad,the booster has a rubber diaphragm in the center. Vacuum is on both sides at around 18 to 20 in. Vacuum. When you step on the pedal which is attached to the interior side of the booster there is a bleed valve that allows air in which also allows vacuum to help the pushrod go towards the master which makes it easy to apply hence power brakes. If your booster is ripped or the internal or external check valves and bleed holes arent working it can cause all kinds of problems. Just hooking it up to straight engine vacuum wont work because it needs to be at the right inches of vacuum. Too much and the pedal will go to the floor, not enough and the pedal will be hard. If you get no air at the bleeders and the brakes are working with out the booster working then I'd bet thats the problem. Dont know how many miles are on the car. You could always call a performance brake parts company and ask for tech help.
This man knows his shit. Good advice bud. I was going to post the same type of info but you said it best so no need.
 

Jaskim06

Active member
207
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i dont have a check valve .. but yes i put the length the correct length
You can get a cheap hand vaccum pump and see if Mrmerc49 is onto the issue. I think the one I got for bleeding brakes from harbor freight has a gauge. Idk. I'd have to go see but I think it does and it's pretty cheap. Or maybe I added one. Idk either way you'd be able to get the right amount of vaccum and tell if it's bad or not. Like I said I've got brand new parts and rebuilt parts that was tested before shipped and they didn't work as they should. Some faulty stuff slips through the cracks sometimes. Especially with all this BS going on for a year and change now.
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