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Old 06-16-2009, 10:00 AM
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Heavy brakes,16Hg vacuum.

Hi, i believe that i might need some help figure this out !
My issue is that i installed a new engine "327" in my 72 nova. It has rather radical cam but the vacuum measures 16Hg at idle (idles @900 rpm) and i also installed new brake booster 7" so he is rather small and the brakes are rather heavy so i installed a vacuum reservoir, did not make any difference. then i inspected the check valves one on the booster and the one that came with the reservoir and they both turned out to be very stiff to suck through, they both worked only one way but like i said they where stiff to suck. The reservoir is mounted on the inner fender maybe 25 inches away from the booster and it is all connected with 3/8 hose. Every thing seems to seal fine when i test the whole thing but my brakes are still heavy !
Any ideas, anyone ?
Thanks. Kristofer

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Old 06-16-2009, 10:11 AM
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Quote:
Originally Posted by Icelander
Every thing seems to seal fine when i test the whole thing but my brakes are still heavy !
If by "heavy pedal" you are saying it takes a lot of pressure, it sounds as though the master cylinder has a piston sized a little large for your particular application, or the pedal ratio is off.

Do the brakes work correctly, other than a hard (heavy?) pedal?

BTW- I doubt that drawing air by mouth will be a very good judge of how the check valves are functioning.
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Old 06-16-2009, 10:21 AM
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Thanks for quick response.
Yes the brakes work like they should but are heavy. ?
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Old 06-16-2009, 10:30 AM
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"it sounds as though the master cylinder has a piston sized a little large"
I am not following you here ?
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Old 06-16-2009, 10:32 AM
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Give us the system specifics please.
master cylinder bore size,
pedal ratio with actual dimensions,
type and size of caliper pistons
and wheel cylinder bore size.
rotor and drum size please as well.

Usually the reservoir will help. A decelerating motor or a motor at cruise will make alot of vacuum, that's when the reservoir charges up.
A 7" booster is not much help, even with good vacuum., the 7" dual booster is better.


Later, mikey
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Old 06-16-2009, 10:32 AM
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Do you mean that i should get a new master cylinder with smaller piston ?
Regards. Kristofer.
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Old 06-16-2009, 10:32 AM
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Quote:
Originally Posted by Icelander
Thanks for quick response.
Yes the brakes work like they should but are heavy. ?
OK- what was the master cylinder supposed to fit, or was it a "universal" (will fit whatever you put it on) application?

What are the specifications on it- mainly the bore/piston size, and is it a "stepped" bore?

What are the details (caliper or slave cylinder piston sizes) of the brakes themselves- OEM or aftermarket, discs all around, disc/drum, drums all around?

One thing you may get away with, is to change the hole that the MC push rod is located in, on the brake pedal. If it's in the top hole, you can try it in the lower hole- but this will increase the distance you have to press, while it makes the pedal easier to push. The push rod may need adjusted, too.

EDIT- Glad you picked up on this, Mikey. OP- you're now in good hands!

Looks like 3 posts in the same minute- pretty good...

Last edited by cobalt327; 06-16-2009 at 10:38 AM.
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Old 06-16-2009, 10:44 AM
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Wow the system spec ?! Then i will need to measure things, i can do that.
But until then i can start telling you that this nova has its original front disc and rear drum set up. Universal booster and master.
I will try the lower set up at the pedal and see if that helps.
Until then,thanks for your help and i will post the results if anyone cares ?
Again thanks for your time and help.
Kristofer.
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Old 06-16-2009, 10:57 AM
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Quote:
Originally Posted by Icelander
i will post the results if anyone cares ?
Please do- I, for one, will surely learn something.

When you change the pedal hole, be sure the push rod maintains the correct position- so that it's not too loose or compressing the MC at rest.
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Old 06-16-2009, 11:13 AM
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There is no such thing as a universal master cylinder. If the rest of the system is stock, with the 2 9/16 single piston calipers and you have a 7" booster, you need a 1" or 1 1/16 master cylinder and you will have a longer than average pedal travel.. You will still have a slightly harder pedal effort. That is the concession you will just have to accept, unless you go to a bigger booster and stock 1 1/8" bore master cylinder..

With a smallblock in a 72 nova you should be able to fit the large stock booster, and it will help your brake issues.

Later, mikey
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Old 06-16-2009, 11:22 AM
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I will, but not until Friday, now i am late for a wedding and to morrow is our Independence day.
Regards Kristofer
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Old 06-16-2009, 11:37 AM
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Quote:
Originally Posted by powerrodsmike
There is no such thing as a universal master cylinder.
So there's no confusion- the "universal" designation was a response to this question from me:

"what was the master cylinder supposed to fit, or was it a "universal" (will fit whatever you put it on) application?"

By "universal", I'm referring to a MC that is sold w/o an actual app, like "fits a 1958 Chrysler New Yorker" type deal, instead is sold by the bore size and it's up to the end user to choose the correct part for the need.

Sorry for the confusion.
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Old 06-16-2009, 12:20 PM
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The confusion was on my part, sometimes I make a feeble attempt at multitasking here at the powerrods command central desk and it backfires on me....duuuuuh ..pass me my drool rag please.



But this is a problem I see so much, where a company will sell a booster/mc combination to a guy and not ask anything about the existing system to see if it will actually work right once installed....then the customer winds up here asking why his brakes are low/hard/soft/high etc....

Later, mikey
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Old 06-16-2009, 12:53 PM
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Old dog there, I see. And I like your pit bull, too!

I can get away with that, sorta- as in "I resemble that remark..." lol
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Old 06-18-2009, 07:17 PM
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OK guys i am back, been in my garage working on those brakes and here is my report.
Moved the rod by one hole on the pedal, great result there.
Then i chanced the check valve on the booster (found one old that fitted) Huge improvement. So the bottom line is my brakes are now working like they should.
So thanks for your help everyone and until next time hope you all will have a great hot rodding.
Regards. Kristofer.

P.S. i know its not Friday, just could not wait.
And point taken, in the future i will be careful when i consider "universal"
Guess i was just lucky this time.
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