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Brake pedal fade

mrbone

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I have a 1968 roadrunner with newly serviced manual drum brakes front & rear.

SYMPTON: Brake pedal is 100% when pumped ounce then applied. But when brake pedal pressure is reduced then applied again, pedal goes to the floor.

The brakes on my first roadrunner I owned in high school would 'fade' the same way.
So I haven't given it much thought.

If it is "normal", is there anything I can do to remedy this?
If not, any ideas what's going on? Seems like bad master cylinder. Wonder if both cars coincidentally had the same problem?

What do you guys think?

THANKS!! AJ
 
pedal going to the floor is not normal. any residue around the top of Master? Have you bleed the lines?
 
Plug the ports on the MC. If you get the pedal to the floor then the MC’s got some issues. Other than that bleed everything again and make sure you have everything adjusted up.
 
OK! That's what I needed to know.
I will block the ports on the MC when I bleed the brakes switching over to DOT5 fluid.
Waiting for new lines to replace the rubber one's on the rear, so when I get them I will start.
 
OK! That's what I needed to know.
I will block the ports on the MC when I bleed the brakes switching over to DOT5 fluid.
Waiting for new lines to replace the rubber one's on the rear, so when I get them I will start.
Not sure about DOT5 in your system. Maybe switch to DOT3 for the older drum system...
 
DOT 5 will be fine IF the entire system is clean/devoid of old fluid.
Mike
 
A long time ago, I read in one of the magazines to flush the system with denatured alcohol when switching to DOT 5. I ran DOT 5 in my Demon years ago - the pedal was firmer with DOT3.
 
Any favorite master cylinders out there for disk/drum?

Looks like Doc Diff has a nice one.
15/16, aluminum and uses factory pushrod..
 
Last edited:
I dont think you can go wrong with Dr Diff,I bought one from summit with the 15/16 size. I googled reviews on the MC, You could look at mancini racing to see what they have.
 
I like the 15/16" manual setup. However, keeping the rear drums adjusted properly is crucial to proper pedal operation. I think that was mentioned in one of the posts above. With either system, if drums are on the car they must be adjusted correctly. Super easy to check and fix, always the first place I start if having pedal issues.
 
Yep I agree its not normal. You should have a firm pedal at all times. If its not the MC, then I would go through the entire system. You could have a weeping wheel cylinder or a leak somewhere in the lines. A small rusty spot in a line will become a big problem when it gives out entirely.
Good luck!
 
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