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Discussion Starter #1
My brakes are good, but when braking hard my pedel will reach the floor.

There is a rather big "lash" before the brakes starts to operates.
I would say that nothing happens the first 30% of the pedal movement when braking. Pedal seems just doesn't get engaged.....?

Is it possible to adjust/minimize the pedal lash?
 

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I know some guys may disagree with me on this, but in fact that is the way my brakes responded after a few miles for over 11 years, and it was very frustrating....and there was NO air in the lines/calipers/system either....

I found the ONLY fix that seems pretty damn permanent for nearly a year now is to replace that damn stupid brake booster with a hydroboost system run off the power steering pump.....the brakes have been very consistantly totally solid feeling ever since....

for the cheep easy way, you may want to try a truck type m/cyl....with a larger bore, less piston travel that way, .....

the brake booster has a mystery spring between the input and output shafts and that is what I think was the design flaw in the unit....there were simply no visible failed parts in my old vacuum booster, I used a truck m/cyl for that reason, and had a firmer pedal, untill going to the hydroboost, then I had such a touchy pedal, I took the opportunity to get an aluminum m/cyl of stock piston size, which restored a more reasonable but very solid feel to the brakes.....

My '72 vette here had the same feel to the brakes as every other GM car of the era....total lack of confidence feeling, me thinks it was a design goal so people would not lock em up, unless totally panicked....safety?? I dunno, learn to drive would be MY response.....
 

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Discussion Starter #4
Play is somewhere 1.5-2"
 

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Discussion Starter #6

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Discussion Starter #8
Did your excessive pedal travel show up after the master cylinder was replaced?
Don't think so, it have always been to much?? free play.
 

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Sounds like you need to adjust the actuation rod between you peddle and the master cylinder to eliminate the free play in your peddle travel. or if there are adjustment holes in your peddle move the rod to a shorter throw...
 

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There is a little bit of plunger adjustment before it enters the master cylinder. Sounds like you may need a little length on yours.

:thumbsup:
 

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You may have a couple of diffrent issues.
Here are a couple of ways to test.

The first is by installing line locks (plugs not solenoids) before the calipers and testing the system. It's tedious, but a good method.

LOW, SOFT or NO PEDAL conditions may not be caused by a failing master cylinder. These symptoms may be indicative of a failure in an ABS unit, vacuum booster unit, soft brake hoses, contaminated brake fluid or air trapped in the system.

The use of line locks (NOT VISE GRIPS) on all brake hoses will allow you to determine whether the problem is at the wheels or higher in the hydraulic system. With locks installed on front and rear hoses, re-check the brake pedal condition. If a low or no pedal condition persists, the problem is between the line locks and the master cylinder. If the brake pedal is high and hard with the line locks on, hold pressure on brake pedal and remove line locks one at a time until the pedal drops. This will identify which wheel or wheels are causing the problem. The use of line locks helps prevent the needless replacement of master cylinders. Line locks have been known to damage brake hoses and should not be used routinely for preventing fluid loss.
Inverted flare caps can be used before the brake hoses. More work, but no damage and foolproof.

Here is one of the best troubleshooters I've seen. Scroll down and you will see booster and rod length areas.
http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm

Here also is a chart of brake pressures that may apply since your engine vacuum is low. Test what your highest reads when you coast after full throttle.
http://www.classicperform.com/PDFs/BoosterBrakePressureChart.pdf

Hope this gives you something to work with.

:D
 

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Discussion Starter #12
Sounds like you need to adjust the actuation rod between you peddle and the master cylinder to eliminate the free play in your peddle travel. or if there are adjustment holes in your peddle move the rod to a shorter throw...
How do I adjust it?

Thanks 010752, I will check the links.
 

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How do I adjust it?

Thanks 010752, I will check the links.
just so we are all on the same page...use your hand and check for far your pedal moves BEFORE you start any brake action.....pull it up and then push down...freeplay (I think) should only be about 3/8"......not enough (rod too long) and your brakes will be applied all the time...adjustment is in the clevis at the pedal, make sure you tighten the lock nut
.....redvetracr
 

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Discussion Starter #14
I did check it earlier today, it's nearly 2" freeplay.

I also took a look behind the pedal, saw the clevis.
The pushrod is attached to the clevis and goes in to some kind of rubber bellow on the other side.

The pushrod have some type of hex end, nearly the same dim as the rod itself.

If I got you right the nut is inside the clevis "vings"?
Have to look closer inside the clevis.....didn't find the adjustment nut.
 

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Discussion Starter #15
This is the end of the rod and a little bit of the clevis is also seen.

It's some kind of hex end but it doesn't look like it's possible to adjust that.
I tryed to loosen the "nut" but it seems like the nut and rod is one piece!!

The adjustment must be done somwhere else, where......?

 

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Discussion Starter #17
Thanks Mike!

Just to get you right before I start remove parts.

If I remove the master cylinder, I can then adjust that rod coming out from the booster?
 

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Yes. Don't unscrew the brake lines on the master. Just take off the two nuts and pull the master forward. You'll see the rod.
Mike
 
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