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Old 08-11-2011, 03:30 PM
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Occasional Soft Brake Pedal, cant figure out why

I am trying to figure out what is happening with the stock manual drum brakes on my 1950 Chevy Sport Coupe. Around town they seem to work fine. This type of driving involves semi-frequent use of the brakes. But, if I drive for a while without using the brakes (i.e. highway or long back road) the pedal will go almost all the way to the floor board before I feel the brakes engage. If I give it once quick pump and then re-apply the brakes, the pedal goes back to normal height when engaging the brakes.



I bled the brakes yesterday and checked the wheel cylinders with no signs of leaks.



Any ideas?

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Old 08-11-2011, 04:49 PM
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air in the lines

If your master cylinder, brake cylinders and front and rear flexible brake hoses are good, you must still have air in the lines. If you are positive that you don't have air in the lines, take a close look at your master cylinder or replace it with a new one (not rebuilt) and bleed the brakes again.
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Old 08-11-2011, 05:06 PM
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I had this same issue with '70 Chevy truck. My problem was contaminated brake fluid. Fresh brake fluid, issue solved.
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Old 08-11-2011, 05:16 PM
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My GUESS is there is some sort of residual pressure valve somewhere that is bleeding back after you drive without hitting the brake for a while. Does it do it after teh truck has sat for a while as well without driving?
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Old 08-11-2011, 08:11 PM
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T-bucket, I have noticed that sometimes when I get in the car before starting it that the brake pedal will go all the way down, similar to what I described in the original post. Even then, one pump and I am good to go.
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Old 08-11-2011, 10:06 PM
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My problem with the '70 Chevy truck was water in the brake fluid. After driving it for some distance, the water would steam. First jab on the pedal, no brakes, second jab it had brakes.
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Old 08-12-2011, 09:47 AM
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I would bleed the system and if it continunes replace the MC.
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Old 08-12-2011, 02:58 PM
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I don't remember if a 1950 chevy had self adjusting brakes on not but this sounds like the brakes might be out of adjustment. The shoes need to be adjusted out close to the brake drum otherwise you use all your pedal travel just moving the brake shoes out to where they begin to touch the drums.
Jack up eack wheel and adjust the shoe out until you can feel it drag and then back it off until it just turns freely, do that for each wheel.

If you don't have self adjusters or if they are not working then you will need to repeat this procedure every 5000 to 10000 miles as the shoes wear down.

Around town and with frequent use the residual valve is holding the shoes out but over time it will bleed back down and then you have to pump the brakes again.
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Old 08-12-2011, 05:05 PM
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I might have a fix... Depending on the master cylinder... Do you have a residual valve in the system?

What happens is that the shoe springs pull the shoes in, pushing the brake fluid back into the master cylinder. You mash the brake pedal you are 'filling the brake cylinder back up till takes the slack out from the springs.

My opinion, find a 10 pound residual valve and plumb into the rear brake line. IT will keep the shoes close to the drum and the shoe springs wont push the fluid BACK into the laster cylinder...
You can find a residual valve in any of the circle track parts houses.

I hope this clears up or helps your problem.
Phil
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