78 Brake Problem
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Joined: Jan 2006
Posts: 55
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From: Munster IN
78 Brake Problem
Just recently applied brakes and pedal felt spongy and went down to almost the floor. I had read a post about the fluid being sucked back into the vacuum assist so I checked my fluid and it was full. I have a gut feeling that the master cylinder is not working correctly. Any help would be greatly appreciated.
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
When you start vette cold,does your pedal go to floor,then pump up some after it warms up good..??? My 78 did that,and it was the MC....they can leak internally cold,then seals expand once fluid gets hot....
Good luck with it...
Rich
Good luck with it...
Rich
Instructor
Joined: Jun 2004
Posts: 182
Likes: 0
From: Sun Peaks British Columbia
I had the same spongy pedal on my 79'. I wound up replacing EVERYTHING, including the proportioning valve, master cylinder etc., all to no avail.
There was a lot of controversy on whether the vacuum boost could be causing a problem.
I finally changed the vacuum booster to a Hydroboost system and now I've got the brakes I've always wanted.
There was a lot of controversy on whether the vacuum boost could be causing a problem.
I finally changed the vacuum booster to a Hydroboost system and now I've got the brakes I've always wanted.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Spongy pedal means air in the lines, bleed them to get it out. THEN you have to find out why it was there. Do you drive your car a lot or does it sit? The original lip seal type calipers tend to leak on ocasion without dripping, The suck air in past the seals. If it does it again, you will need to rebuild or replace the calipers and verify the runout on the rotors. If oyu do a search in here you will find a bunch of threads on the subject.
Drifting
Joined: Jan 2005
Posts: 1,438
Likes: 3
From: Florissant MO
Might as well change out the MC anyway. They are only about $30 at Autozone, Advance or NAPA. You will also need about a quart of BF to bench bleed the MC and the rest to bleed all of the calipers. You should be able to find out what is exactly the problem after bleeding the system.
Before you do all of that, check the vacuum hose from the intake manifold to the booster to see if it has any cracks and may be leaking air.
Just my humble opinion. I'm going through the same thing right now, only mine are manual brakes.
Before you do all of that, check the vacuum hose from the intake manifold to the booster to see if it has any cracks and may be leaking air.
Just my humble opinion. I'm going through the same thing right now, only mine are manual brakes.
