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Old 08-27-2011, 05:38 PM
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Excessive Brake Pedal Travel

My 1941 Chevy's brakes work fine, I just have too much free travel before the brakes start working.

It's a power brake system with front disc's and back drums. The proportioning valve is on the frame well below the MC and booster. The pedal travel has been like this since I bought the car 3 years ago.

I have replaced the brake fluid, bled the system, and adjusted the rear brakes with very little improvement.

I recently taped 3 small nuts together and put them into the MC where the booster rod would go. It brought the pedal up but also applied the brakes so I took them out. Did I just prove that the brake pedal rod is too short?

I looked at my brake pedal rod to see if it's adjustable, it doesn't seem to be unless the adjustable part is on the other side of the firewall and into the booster.

Can I buy a longer brake rod? Do I have to lengthen the current brake rod? Any help would be greatly appreciated.

Russ
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Old 08-29-2011, 04:14 PM
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Sounds to me like your pedal travel is too long (under dash stop adjustment), or the pedal swing geometry is wrong, and the rod too long lifting the pedal to that high position. Do you need all that travel?

I've seen brake pedals (hanging) with multiple holes to mount the push-rod to that would lower the pedal. On some GM power booster to MC plunger, there are different length push-rods as well, two sizes I'm aware of, that would effect plunger depth, too short and it doesn't push enough fluid, too long it bottoms out in the MC.
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Old 08-29-2011, 05:12 PM
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Quote:
Originally Posted by 68NovaSS
Sounds to me like your pedal travel is too long (under dash stop adjustment), or the pedal swing geometry is wrong, and the rod too long lifting the pedal to that high position. Do you need all that travel?

I've seen brake pedals (hanging) with multiple holes to mount the push-rod to that would lower the pedal. On some GM power booster to MC plunger, there are different length push-rods as well, two sizes I'm aware of, that would effect plunger depth, too short and it doesn't push enough fluid, too long it bottoms out in the MC.
Yes, way too much travel before brakes are applied. Can I remove the rod from the pedal and go buy a longer one? My brake pedal is straight in the area where the rod attaches so I don't think I'd get much more travel if I lowered the rod on the pedal. The rod is supposed to be horizontal as much as possible right?
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Old 08-29-2011, 06:23 PM
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If the travel is really "free", i.e. the pedal/rod assembly does not contact the piston until the pedal is depressed some distance, then there are a couple choices:

Lengthen the push rod.

Adjust/modify the pedal stop.

Usually a power MC piston will have a shallow push rod hole, or will use a spacer to make it that way. So be sure the MC itself and the MC piston's push rod hole is compatible w/the pushrod you're using.


If there IS contact w/the piston after just a little pedal movement, yet it still takes a lot of travel to get the brakes to engage, the master cylinder bore may be too small or the calipers/wheel cylinders too large or the pedal ratio is too high. Try the lower hole first (if you have one, that is).
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Old 08-29-2011, 07:43 PM
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Another thread reminded me- is the MC on the firewall or below the level of the calipers, or ?
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Old 09-01-2011, 06:15 PM
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Quote:
Originally Posted by cobalt327
Another thread reminded me- is the MC on the firewall or below the level of the calipers, or ?
The MC is high on the firewall.

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Old 09-01-2011, 07:33 PM
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Another thought, I came up against when putting all discs on my Nova, in the late '80's, some manufacturers came up with what they called a Quick Takeup MC, designed to work with brake systems where the pads didn't make full time contact with the rotor, they had a longer stroke to take up the slack before apply. It was to help with mileage requirements, cut drag. Any chance you have one?
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Old 09-01-2011, 07:56 PM
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If three nuts were too much, how about trying two? Or one?
That might tell you how much to lengthen the rod.
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