Brake booster?
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Elder User
Joined: May 2005
Posts: 537
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From: Graves County, KY
Brake booster?
I notced over the last few days that when I was at a stop light my brakes seemed to ease themselves off after a minute or two. Yesterday I suddenly have no power brakes. The pedal goes 3/4 of the way to the floor and then I have what feels like manual brakes from there.
Is this a bad brake booster?
Is this a bad brake booster?
New User
Joined: Jan 2008
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There is a brake booster test, It involves the engine being shut off and apply the brakes then with your foot on the pedal start the engine.
Send me an e-mail for the actual instruction.
Otherwise What I think it is .....the Master cylinder going south
Send me an e-mail for the actual instruction.
Otherwise What I think it is .....the Master cylinder going south
Fleet Mechanic
Joined: Mar 2004
Posts: 1,398
Likes: 17
From: Hesperia, CA
I don't know what size engine you have, but if it is leaking you had better fix it fast. My 460 started leaking and I just let it go for a couple of months. It turns out that the cold air from the leaking booster was going right to the #7 cylinder. This warped the intake valve on the #7 cylinder. It is no fun getting that 80 pound plus intake manifold and the equally heavy head off to get the valve replaced.
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Elder User
Joined: May 2005
Posts: 537
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From: Graves County, KY
It's a 302. The master cylinder is less that a year old, but the P.O. did it and I don't know what quality of part he used.
Mil1ion, msg on the way.
Mil1ion, msg on the way.
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Fleet Mechanic
Joined: Mar 2004
Posts: 1,398
Likes: 17
From: Hesperia, CA
Hey Dennis, I fought rebuilt master cylinders for a lot of years, so it is nothing new. I found out a couple of years ago that a new master cylinder is only about 30 percent more so I opted out for a new one on my 77 and haven't had a problem since.
Gary
Gary
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Elder User
Joined: May 2005
Posts: 537
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From: Graves County, KY
ok, so I pumped the pedal a couple of times, started it while pushing on the brake and the pedal did drop down.
If I press the pedal repeatedly, it sputters and wants to die. If I hold the pedal, the idle drops slightly.
I clamped off the vacuum to the booster with vice grips, then released them and it stumbled then recovered.
So is this indicative of a bad booster or MC? I'm still leaning toward the booster.
If I press the pedal repeatedly, it sputters and wants to die. If I hold the pedal, the idle drops slightly.
I clamped off the vacuum to the booster with vice grips, then released them and it stumbled then recovered.
So is this indicative of a bad booster or MC? I'm still leaning toward the booster.
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Elder User
Joined: May 2005
Posts: 537
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From: Graves County, KY
Thanks Dennis, I will test it out this afternoon. BTW, I have already checked the whole system and there are no leaks an no apparent loss of fluid in the MC. The wheel cylinders appear to have been changed at the same time as the MC by the PO.
New User
Joined: Jan 2008
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In this case of a faulty MC.....the fluid doesn't leak out of the system.
It leaks passed the piston seals from the line back into the master cylinder
This action causes the pedal to drop....the vehcile to start rolling as there is no resistance from hydraulic pressure... to keep the pedal up where it should be.
It leaks passed the piston seals from the line back into the master cylinder
This action causes the pedal to drop....the vehcile to start rolling as there is no resistance from hydraulic pressure... to keep the pedal up where it should be.
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Elder User
Joined: May 2005
Posts: 537
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From: Graves County, KY
OK I see. If that's the case, would I still have manual brakes at the lower 1/3 of the pedal? It seems that if the seals failed, then I would get no braking at all.
Of course I'm just brainstorming - not trying to be argumentative. I'm at work right now and can't actually test anything.
Of course I'm just brainstorming - not trying to be argumentative. I'm at work right now and can't actually test anything.