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Topic: Brakes lose pressure with motor running...?

in Forum: C3 Handling Components

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Brakes lose pressure with motor running...? (1/5)
8/27/11 8:35pm

Navyaq
Former Member
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Champaign, IL - USA

Vette(s):
1977 USA VETT... I am a Navy Vet and bought this car from a guy that's in the Army. He started the USA theme on this previously yellow yard decoration that he found. Now it is my turn to add to this tribute to Country and those that defend her.

Joined: 9/25/2010
Posts: 13

So I had a leaky caliper issue and very little front breaks (if any?). I I replaced the seals on both sides and found that either I know nothing about repairing breaks or my calipers themselves were bad... either way, I replaced both front calipers and BINGO! no more leaks. I bled the system (front and back) had great pedal pressure right up until I started the engine.... :-(

Right to the floor! I could hear air at the pedal. The dust boot is old (probably the original) and ripped. In reading my Haynes Manual I found that there is an air filter behind that boot. I see a clip that holds the push rod to the pedal (Question #1.... how does one get this clip off?)

Realistically, I don't think this is the issue which leads me to ask (Question #2) How does one check the vacuum boost to see if that is the problem? I have suction at the front, I took the hose off and fired her up... damn near sucked my son down the hose (so he said when he let go of it and killed the motor).

Any suggestions are welcome!!

Thanks in advance,

Navyaq

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Re: Brakes lose pressure with motor running...? (2/5)
8/28/11 10:28am

rraider1
Former Member
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Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion

Joined: 10/14/2003
Posts: 1165

Let us know what year and some specs on the car this might help

you may still have some air in the system this is the bleeding order

Left rear inner

Left rear outer

Right rear inner

Right rear outer

Left front

Right front

Bleeding the breaks can be a son of a gun

https://www.c3vr.com/member_uploads/4201_4300/4221/9C57D_Master_cyl_and_Booster_Assy.JPG

|UPDATED|8/28/2011 7:28:16 AM (AZT)|/UPDATED|

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Re: Brakes lose pressure with motor running...? (3/5)
8/28/11 12:06pm

My bad... Let me try this again....

I have a 1977 Corvette (just like the one pictured and mentioned on my profile page).

To keep the post somewhat short; When I bought the car (about a year ago) the brakes were a little spongy. I saw that they were leaking fluid on the inside front tires and figured it would be nothing more than a (simple) brake job...

Finally having the time to take care of this (long story short) I replaced the front calipers. The bleed job went as smooth as any of the other bleed jobs I've done in the past 30+ years (just saying, NOT my first time bleeding brakes).

With firm pressure on the pedal and big smile on my face (finally get to do a little power braking burn out for the Facebook page), I started up the engine and hit the brake pedal and squissssh.... all the way to the floor they went.

Back to the drawing board I went. All four tires off now and did the full blown bleed job (passenger rear inside, outside, driver rear inside, outside, passenger front, driver front.) Once again, great pressure on the pedal until I fired up the engine.

I did manage to get the brake light to go out by doing some minor power braking... Back breaks hold as good as one would expect, front are not holding at all it would seem. With my foot on the brake and in gear the rear end will squat real low (which is kinda cool looking) but give it enough gas (not talking a lot here) and there's just not enough brake to hold it in place. By doing this, it becomes obvious to me the back brakes are doing their job and the front are not .... at all it would seem.

I jumped on the vacuum assist (brake booster) because "vacuum" seems to be the only difference between engine on and engine off... after doing some reading, it doesn't seem that what I have described would be caused by the booster going bad (my brakes should be harder to push with a bad booster.... right?)

I have seen some talk about a proportioning valve/switch... going to go take a look see now.

So much for keeping this short...

Any help will be appreciated.

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Re: Brakes lose pressure with motor running...? (4/5)
8/28/11 4:56pm

rraider1
Former Member
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Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion

Joined: 10/14/2003
Posts: 1165

When I first got my 77 it was similar but I had front brakes no rear, bleeding these can be a pain. I have used each method vacuum bleed, old pump and bleed (2 people), power bleeding, each for different problems. it can be difficult to get the proportioning valve to reset, mine would not reset by pump and bleed It reset using sa vacuum bleeder. If at first the light was on you would not have been able to bleed that section because it was shutoff, once you got the light to go out you would need to re bleed. if your still having trouble and some of the experts do not get bin the right direction pm me with email and I can send you some good articles on the breaks

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Re: Brakes lose pressure with motor running...? (5/5)
8/28/11 9:53pm

Stops on a dime now!! Man I love my car!

Master cylinder... Bingo!

I figured my son wasn't giving the brakes the college try while pumping so I got my wife to join in the fun (she is the best). After another full blown bleed job... same thing. The master cylinder looked like a big chunk of rust sitting under the hood anyway so I decided today was the start of the engine bay clean up...

While I yanked the old one out she went to get me a new "pretty" one, some Mike's Hard Lemonade and more brake fluid.... While she hooked me up with a tall cold one I blead the master out before putting it in the car. I put my boy in charge of putting the car up on jacks and spinning the lug wrench.... Bleeding was quick and painless. Good solid breaks in the drive which meant road test! Off to Starbucks (other side of town) with my number 1 wrench turner.

My son got to park the Vette so he didn't mind being considered #2.

All in all, great fun now that we are up and running!

Thanks for your input.

Navyaq

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