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 Post subject: Brake question
 Post Posted: Tue Dec 08, 2009 3:58 pm 
 
Hoping someone can help me out. Got power brakes on my car and have very good vacuum to the booster, but when I push on pedal really hard engine rpm's go up about 200 rpm.Can someone steer me as to what could be wrong.


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 Post subject: Re: Brake question
 Post Posted: Tue Dec 08, 2009 5:22 pm 
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Sounds like you got a vacuum leak in or around the booster diaphragm somewhere? This is probably happening while driving too but you just don't notice it cuz the RPM is up some anyway. If you disconnect the vacuum line to the booster just to test it (don't drive with it disconnected!) this should stop. If it does, that pretty much points to the booster diaphragm.

We got a couple of mechanic types on here so I'd wait and get a second opinion from them before you go and tear it apart.

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 Post subject: Re: Brake question
 Post Posted: Tue Dec 08, 2009 8:59 pm 
 
Well I kind of thought that that might be the problem being that it is a older 68 vette. If it is , I wont be looking forward to doing. I also forgot to mention that the pedal is pretty hard. Would a vacuum check valve help me out? If not I guess it's booster time.


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 Post subject: Re: Brake question
 Post Posted: Tue Dec 08, 2009 9:37 pm 
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That booster vacuum line already has a check valve in it where it connects to the housing. You may be driving without any PB booster! If you disconnect and plug the hose going to the booster and then check the pedal again, this might confirm that as well.

How much cam is in this engine? Big overlap cams also cause vacuum problems for power brakes. Might be the cam but to be honest, if the engine RPM is going up that much when the brakes are applied, there has to be air going thru that diaphragm to make that happen.

In 1969 some Z28 Camaros weren't offered with power brakes. Those were the ones that were ordered with the "off road" cams in'em. They also didn't have hide away headlights for the same reason, ie, vacuum operated the headlight doors.

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 Post subject: Re: Brake question
 Post Posted: Tue Dec 08, 2009 10:15 pm 
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I think Ken's steering you in the right direction. You might want to put a vacuum gauge on it to make sure you have enough vacuum to start with. If it's leaking vacuum while you're holding the brake down the booster is bad. The elbow that pushes into the grommet on the booster should have a check valve in it. Check that to make sure it's working but even if it is you shouldn't have vacuum leaking with the brake applied and you should have some assist at idle.

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 Post subject: Re: Brake question
 Post Posted: Wed Dec 09, 2009 7:02 am 
 
Thanks again for the info. It's gonna be a while before I get to it now as I ended up with a bad reaction from some anti-infection medication for a ear ache and ended up with the hives ( itchy $**t ) and we just got dumped on with 9" of snow with more on the way


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 Post subject: Re: Brake question
 Post Posted: Fri Dec 11, 2009 11:59 am 
 
Ken0069, The specs on the cam are;
adv specs. int 286 w/581 lift
exh. 290 w/573
dur @ .050 int 242 exh 250
lobe sep.112 degreed in w/ lobe center method on intake centerline @ 108 per crower specs.
Again, the car seems to stop fine but when you push that little extra at a stop rpms jump 100 to 200 and there is no check valve in booster line anywhere


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 Post subject: Re: Brake question
 Post Posted: Fri Dec 11, 2009 6:49 pm 
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speedy427 wrote:
there is no check valve in booster line anywhere


Not alot of cam so that shouldn't be a problem. There is suppose to be a check valve in that line somewhere? Most of that year of GM car came with the check valve mounted directly to the booster housing that was a 90* fitting with the hose connected to that and run to the manifold vacuum port. Here is what that check valve looks like and BTW, this is one for a 1968 Vette.

http://www.napaonline.com/Search/Detail ... 12+2012030

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 Post subject: Re: Brake question
 Post Posted: Mon Dec 14, 2009 10:10 am 
 
Well Ken, you were right. There is a check valve in my line ( put your glasses on ). Anyways, vacuum tested the booster and it leaks down. Thanks again for the help. =D> [-(


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