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PostPosted: Thu Jan 18, 2018 4:22 pm 
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EFI Slant 6
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Location: Portland, OR
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Well the alignment is done and now that it rolls it needs to stop safely. When I swapped in the Ford 8.8 rear end I wound up with rear discs, and I just installed front discs. My current master cylinder is 15/16'' bore and has an unsafe amount of pedal travel, as in almost to the floor. The front calipers piston bore is 2.935'' and the rear piston bore is 1.875'' (1 7/8'').

What would be a better master cylinder choice?

Cheers,
Barnaby

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PostPosted: Thu Jan 18, 2018 5:29 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
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Location: So California
Car Model*: 64 Plymouth Valiant
Is there air in the lines?

Can you change the rod mount location on the pedal?

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes
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PostPosted: Thu Jan 18, 2018 6:20 pm 
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EFI Slant 6
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There is no air in the lines. I considered that myself, but I had my shop bleed the brakes and they are confident there is no air. I don't think I can change the rod mount location on my pedal? The shop believes the bore diameter is too small. Typically I am skeptical of mechanics, especially on our older cars. But I have a high degree of confidence in these guys.

B

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PostPosted: Thu Jan 18, 2018 6:45 pm 
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My Desoto has 11 3/4 mopar front and the 8.8 Ford rear brakes.

I use a 1.03 GM aluminum master cylinder and ancient Wilwood prop valve. I gutted the GM dist valve metering section.

It took me a while to get things the way I wanted them with this setup. In the end EBC Yellow front pads and a good adjustment on the prop valve sorted it out.

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PostPosted: Thu Jan 18, 2018 6:52 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
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Location: So California
Car Model*: 64 Plymouth Valiant
Are they power?

Other than pedal travel, how do they feel?


A larger bore will decrease pedal travel by the square of the ratio between new and old diameter.

Assuming 10" travel (after free play is taken up)

An increase to 1" will be ..... 10 / ((1 / (15/16))^2) = 8.8.
With the shorter travel, you'll need more pedal pressure


With non-power brakes, too large an increase in bore will make the brakes too hard to apply.

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

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PostPosted: Thu Jan 18, 2018 7:27 pm 
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EFI Slant 6
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Location: Portland, OR
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Thanks, I forgot to mention that it has manual brakes.
And I thought about the bigger bore requiring more effort since that was the problem on my Valiant and wound up going to a smaller bore and was much happier. That is why I installed the 15/16th in this car. What about an adjustable rod? I had a similar problem on a 1960 Dodge years ago, the rod worked, but my learning curve was long and it initially wasn't releasing pressure. Eventually I found the correct adjustment.

And I've seen the GM aluminum MC's and they look great. How much work is it to retrofit into my Dodge?

Thanks

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PostPosted: Thu Jan 18, 2018 8:14 pm 
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I think you need a larger-bore master cylinder of one kind or another. 15/16" strikes me as not nearly big enough to provide enough fluid volume with reasonable pedal travel for those large front calipers and now rear calipers, too, no matter how you rig things.

You may wind up needing a booster, if low pedal effort needs to be part of the equation.

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Last edited by SlantSixDan on Fri Jan 19, 2018 7:08 am, edited 1 time in total.

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PostPosted: Thu Jan 18, 2018 11:35 pm 
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Supercharged

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Car Model*: 64 Plymouth Valiant
Sandy,

What are your caliper piston sizes?

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

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PostPosted: Fri Jan 19, 2018 6:20 am 
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Location: Blacksburg, VA
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It is a light car, so I would go with 1.03 MC, or maybe one more step up. Manual should still be fine. I have big pistons on my Darts and use that size MC and they are fine to stop w/o boost/power. I am a little suspicious that you still might have air in the lines, and/or the pedal pushrod should be made longer. How high is the pedal from the floor at rest now (no pedal application)?

Lou

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PostPosted: Fri Jan 19, 2018 9:04 am 
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The pedal is about an inch off the floor and it wont come up with pumping. What application is the 1.03? Drum/drum or disc/drum?

Thanks
B

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PostPosted: Fri Jan 19, 2018 1:41 pm 
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An inch off the floor when depressed, or before depressing the pedal? I am trying to find out how high it is when your foot is NOT on it.

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PostPosted: Fri Jan 19, 2018 4:17 pm 
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It is all the way up.

B

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PostPosted: Fri Jan 19, 2018 4:19 pm 
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Location: SW Washington
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Lobster1 wrote:
It is all the way up.

B


And how far in inches is that from the floor?

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PostPosted: Fri Jan 19, 2018 4:31 pm 
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I would need to go to the shop in order to check. I'm away from the car for a week as I'm leaving town again for sales.

B

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PostPosted: Sun Jan 21, 2018 9:07 pm 
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I am on the road right now....I will have some answers for you late in the week.

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