brake problems
Thread Starter
Intermediate
Joined: Jan 2012
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brake problems
Have recently converted my 72 with manual brakes to power brakes with new power booster and master cylinder the car stops well but the pedal goes to the floor[brakes are still on with pedal to the floor]with engine off I have a good hard pedal.the car has all rebuilt calipers and new brake hoses,there are no visible signs of leaks anywhere, have a good vac source from back of carb, its losing pressure somewhere,got me baffled any ideas ??? Thanks Alan
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
Have recently converted my 72 with manual brakes to power brakes with new power booster and master cylinder the car stops well but the pedal goes to the floor[brakes are still on with pedal to the floor]with engine off I have a good hard pedal.the car has all rebuilt calipers and new brake hoses,there are no visible signs of leaks anywhere, have a good vac source from back of carb, its losing pressure somewhere,got me baffled any ideas ??? Thanks Alan
Or did you mean it goes to the floor, too much travel, but brakes hold?
Did you disconnect any lines to the master cylinder?
Master cylinder ever run out of fluid?
If so, could be a bleeding issue.
The master sometimes needs to be bench bled.
I've done it on the car but only after jacking the rear of the car up very high to get the master tilted downward slightly, allowing bubbles to escape.
Does the push rod from the booster begin to enage with the master cylinder around the point where the master is nearly tightened to the booster? I did a similar conversion years ago, rod was too short, too much pedal travel before the master began to engage.
Thread Starter
Intermediate
Joined: Jan 2012
Posts: 45
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Are you saying the pedal goes to the floor and stays there?
Or did you mean it goes to the floor, too much travel, but brakes hold?
Did you disconnect any lines to the master cylinder?
Master cylinder ever run out of fluid?
If so, could be a bleeding issue.
The master sometimes needs to be bench bled.
I've done it on the car but only after jacking the rear of the car up very high to get the master tilted downward slightly, allowing bubbles to escape.
Does the push rod from the booster begin to enage with the master cylinder around the point where the master is nearly tightened to the booster? I did a similar conversion years ago, rod was too short, too much pedal travel before the master began to engage.
Or did you mean it goes to the floor, too much travel, but brakes hold?
Did you disconnect any lines to the master cylinder?
Master cylinder ever run out of fluid?
If so, could be a bleeding issue.
The master sometimes needs to be bench bled.
I've done it on the car but only after jacking the rear of the car up very high to get the master tilted downward slightly, allowing bubbles to escape.
Does the push rod from the booster begin to enage with the master cylinder around the point where the master is nearly tightened to the booster? I did a similar conversion years ago, rod was too short, too much pedal travel before the master began to engage.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
The brakes engage near the top of travel and stop the car but end up at the floor I have bench bled the MC and have bled the brakes 3 times the first time in put it in the clevis was a bit long which meant the brakes were slightly on all the time BUT I had a Good Hard Pedal,changed the clevis to the correct one but had to pull the pedal down a little bit[maybe quarter inch]maybe I have to adjust the clevis again ?? wouldn't of thought that would make such a difference but Thanks Alan
Thread Starter
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Did you change the master cylinder? The Parts and Illustration Catalog, 53 - 82, shows a different master cylinder for manual brakes. Part #1800118 for manual brakes, 1.0" diameter cylinder. Part #18001004 for power brakes, 1.125" cylinder diameter. The MC for power brakes would displace more fluid per unit of travel than the manual version does. This may explain why you're getting excess pedal travel? The assembly manual shows a different part # for the MC with power brakes as well.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
I bought a manual to power brake conversion kit from Jegs,comes with new Booster,MC clevis and instructions,as I said the first time I put it in the brakes were on slightly BUT I HAD A HARD PEDAL, when I used the brakes,now since I changed the clevis to the correct one and shortend the pedal travel about quarter inch,car stops well but pedal goes to floor,when pedal is at the floor brakes are on !!!!
Thread Starter
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How much pedal travel do you get before seeing fluid movement? Maybe open a bleeder, see how far the pedal travels before you see fluid start to squirt? Thought is maybe there's an issue with your linkage. I noted the JEGS site mentioned 2 pins supplied. Were these the pin between the master and booster? I had an issue like this when I changed over, pin was too short, too much pedal travel before the master began to engage.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
From what you describe it seems the pedal hitting the floor began when you shortened the throw. There may be a spec for this in the assembly manual. I'll look when I get some time. I recall there is a spring which keeps the brake pedal up against a stop. Have you tried lengthening this rod again, maybe by half the distance you had shortened it? See if this helps.
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It's conceivable you've got the wrong power booster and/or wrong lengths/type of booster rods. If I recall, there were changes in the booster design somewhere post '79. If you purchased rebuilt parts, it's quite possible the wrong ones were spec'ed for your '72.
I know this because I went through the same thing last year when I was re-doing the brake system in my '76. Turns out the supplier sent me a mis-marked package; it contained a booster/rod for an '80 Vette.
Live. Learn.
I know this because I went through the same thing last year when I was re-doing the brake system in my '76. Turns out the supplier sent me a mis-marked package; it contained a booster/rod for an '80 Vette.
Live. Learn.
Thread Starter
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Joined: Jan 2012
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It's conceivable you've got the wrong power booster and/or wrong lengths/type of booster rods. If I recall, there were changes in the booster design somewhere post '79. If you purchased rebuilt parts, it's quite possible the wrong ones were spec'ed for your '72.
I know this because I went through the same thing last year when I was re-doing the brake system in my '76. Turns out the supplier sent me a mis-marked package; it contained a booster/rod for an '80 Vette.
Live. Learn.
I know this because I went through the same thing last year when I was re-doing the brake system in my '76. Turns out the supplier sent me a mis-marked package; it contained a booster/rod for an '80 Vette.
Live. Learn.