Replacement Master cylinder for 70, and low pressure question. - Vintage Mustang Forums
 
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post #1 of 11 (permalink) Old 09-20-2019, 02:12 PM Thread Starter
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Replacement Master cylinder for 70, and low pressure question.

I am looking for a quality master cylinder for my 70 351C Mach. The one i have now was bought in a moment of weakness at Auto zone and I needed to step up the connections and it leaves almost no room for error and busted knuckles.
I am looking for a replacement that's good and will fit the stock brake lines with no adapters. (front is disk back is drum)

I'm trying to find out why my rears have no pressure. the fronts bleed with perfect pressure but backs dribble. So I am thinking there is a hole somewhere. but I have no leaks or puddles.
I put in new lines and completely new brakes all around, new modulator valve, cylinders, DOT 5 synthetic fluid. Backs keep locking up after bleeding.
any ideas?
Thanks guys
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post #2 of 11 (permalink) Old 09-20-2019, 02:27 PM
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New rubber hoses?
Possibly your shuttle valve in the proportioning block has shifted blocking the fluid to the rear.
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post #3 of 11 (permalink) Old 09-20-2019, 05:40 PM Thread Starter
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I used a special bolt to prevent that, good thinking though.
All new rubber.

this is like the bolt i used https://www.ebay.com/i/152216419694?...xoCO8EQAvD_BwE
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post #4 of 11 (permalink) Old 09-20-2019, 06:14 PM
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There is NO blockage when schuttle shifts left or right. Only brake light on dash id effected.
What system do you have?
Factory Front disc, rear drums which means a booster.
A non booster system with front disc/rear drums, which did not exist in 70.
Is it the master, distribution block, improper plumbing.
Which booster if you have one? A stock type factory, or a will fit "if" booster that is supplied by MANY aftermarket suppliers that have different bolt patterns, different bore depths in master, ON and ON. All these are factors.
OLD saying. One size does not fit all.

Last edited by CHOCK; 09-20-2019 at 06:23 PM.
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post #5 of 11 (permalink) Old 09-20-2019, 11:18 PM
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Two months ago, I swapped out master cylinders on my '70 convert. I used a Tuff Stuff master cylinder, bought from eBay. Easy swap, looks good and reasonable price.
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post #6 of 11 (permalink) Old 09-21-2019, 12:40 AM
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Quote:
Originally Posted by CHOCK View Post
There is NO blockage when schuttle shifts left or right. Only brake light on dash id effected.
What system do you have?
Factory Front disc, rear drums which means a booster.
A non booster system with front disc/rear drums, which did not exist in 70.
Is it the master, distribution block, improper plumbing.
Which booster if you have one? A stock type factory, or a will fit "if" booster that is supplied by MANY aftermarket suppliers that have different bolt patterns, different bore depths in master, ON and ON. All these are factors.
OLD saying. One size does not fit all.
get chocks advise mate or even better get the required parts from him . did so for my 70 351c front disc and rear drums when the brakes failed and now working perfectly.
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post #7 of 11 (permalink) Old 09-21-2019, 10:47 AM Thread Starter
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The booster is factory as is the disk/drum setup, I got the plumbing from Virginia classic (brake lines) and the master cylinder was from auto zone. all the rest of the parts i replaced 1 for 1 with exact same.
the cylinder might be the issue ?? i thought it might be and replaced it in the lifetime warranty at AZ but it didn't fix the issue.
So next I replaced the factory Modulator valve with a Scott Drake, didn't fix it either.

CHOCK do you have a parts list and price list you can DM me? I am at a loss and want to get it up and going.

As i was saying above. when i bleed the brakes. the fronts squirt up and hit the upper fender well. but the backs basically dribble. (its getting expensive since i use silicone haha)
This is the only issue left (i hope) thats keeping me from driving my car that I have had since 1984 and probably only driven it 100 miles testing stuff after adding or fixing. (I am the king of procrastination)
Thanks again for any input!!
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post #8 of 11 (permalink) Old 09-21-2019, 04:52 PM
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Writing a novel, texting volumes, will never replace one human conversing a situation one to one.
Plus my one finger typing makes me tired.
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post #9 of 11 (permalink) Old 09-23-2019, 09:36 AM Thread Starter
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Quote:
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Writing a novel, texting volumes, will never replace one human conversing a situation one to one.
Plus my one finger typing makes me tired.
Ok, Makes sense, I will reach out soon!!
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post #10 of 11 (permalink) Old 09-23-2019, 11:03 AM
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Check to make sure your pushrod isn't too long, preventing the master cylinder piston from returning all the way to "rest".

Bart

What, me worry?
- Alfred E. Neuman

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post #11 of 11 (permalink) Old 09-23-2019, 01:26 PM Thread Starter
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Check to make sure your pushrod isn't too long, preventing the master cylinder piston from returning all the way to "rest".
Never thought of that!! i ASSumed it was all ok since it was stock.
Will check, Thanks
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