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Discussion Starter #1
Finally got around to bleeding the brakes on my Nova this week, but aren't satisfied with the pedal, it's low, but appears to stop the car.

Here's what I have:
  • Stock-type GM Master Cylinder (came with my Heidt's front sub-frame) - 1" bore
  • GM Metric discs in front (came with the Heidt's front sub-frame)
  • 1970 Roadrunner 11" drums in rear with 15/16" wheel cylinders
  • Thru-frame fittings in front brake lines to each wheel
  • Hurst Line Loc - (shouldn't be an issue)
I'm thinking I need to go to a master cylinder with an 1 1/8" bore - because I can't get enough fluid to fill up the rear wheel cylinders and those thru-frame fittings.

Stock 1969 Chevelle SS disc/drum master cylinder will fit and has 1 1/8" bore.

Any comments?

Thanks in advance.
dc
 

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I was going to switch from 1 1/8 to an 1" bore because of the extra effort to stop my car. I bought mine by accident and have been using it until the end of the season. You can have mine, just pay the shipping.
 

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Are you still using the factory 1/4 inch lines??

If so change the lines to 3/16

IMO
AL
 

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Are you still using the factory 1/4 inch lines??

If so change the lines to 3/16

IMO
AL
Changing brake line size wont change any brake performance.:no:

Increasing MC bore will increase your pedal effort and decrease your pedal travel. Decreasing MC bore will decrease your pedal effort and increase your pedal travel.
 

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Changing brake line size wont change any brake performance.:no:

Increasing MC bore will increase your pedal effort and decrease your pedal travel. Decreasing MC bore will decrease your pedal effort and increase your pedal travel.

+1

If you "don't have enough volume to fill the wheel cylinders and calipers" then you don't have it adjusted right or bled right. Increasing the MC bore will definitely make it harder to push the pedal - enough that it might be a concern if you don't have power brakes.
 

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Discussion Starter #6
Are you still using the factory 1/4 inch lines??

If so change the lines to 3/16

IMO
AL
Front lines are 3/16", rear is 1/4".


Increasing MC bore will increase your pedal effort and decrease your pedal travel. Decreasing MC bore will decrease your pedal effort and increase your pedal travel.
This is my line of thought..

If you "don't have enough volume to fill the wheel cylinders and calipers" then you don't have it adjusted right or bled right. Increasing the MC bore will definitely make it harder to push the pedal - enough that it might be a concern if you don't have power brakes.
I have manual brakes. I notice that the HP cars of the 60's had big bore MC's (Chevelle SS's, Mopar's Road Runners, etc.). I'm going to re-do the bleed process this weekend, but don't think it's going to give me the pedal I'm looking for.

Any other thoughts/comments? Many thanks.

dc
 

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Yes, the line size will not have any bearing on brake performance. The MC bore size will result in what was already mentioned with regard to pedal travel and effort. My question is what kind of proportioning valve are you running, and is it adjustable?
 

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I have a mopar unit, 1 1/32" bore, aluminum casting/plastic resorvoir... very lightweight and works very well on my disc/drum setup.
Available at any auto parts store, new or reman, about 30-$50. Mid 80's full size rear drive cars.
Will need to elongate mounting holes slightly to fit studs.



 

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have you checked the pedal ratio? with manuals you should be at around 6.0 and up....

as for Bore.. NOGO pegged it.. if anything you would be happier with a 7/8" to 15/16" bore

I would like to find a stock 7/8" bore GM 4wheel disk MC..for my 4wheel disk app. but alas.... they do not exist... that I know of...
 

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Finally got around to bleeding the brakes on my Nova this week, but aren't satisfied with the pedal, it's low, but appears to stop the car.

Here's what I have:
  • Stock-type GM Master Cylinder (came with my Heidt's front sub-frame) - 1" bore
  • GM Metric discs in front (came with the Heidt's front sub-frame)
  • 1970 Roadrunner 11" drums in rear with 15/16" wheel cylinders
  • Thru-frame fittings in front brake lines to each wheel
  • Hurst Line Loc - (shouldn't be an issue)
If you have a disc/drum setup and are not running a combination valve (prop and metering valve in one) you will have a low pedal with "satisfactory" brake performance. The metering valve allows the rear pressure to take up slack between the drum and shoes before the front brakes are applied. The proportioning valve applies the proper pressure bias between the front and rear brakes.
 

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Changing brake line size wont change any brake performance.:no:

Increasing MC bore will increase your pedal effort and decrease your pedal travel. Decreasing MC bore will decrease your pedal effort and increase your pedal travel.
Been down this road many times and I will not argue about it.

your dealing with pressure and flow rates.

The line size has a effect on flow rate! FLOW RATE HAS A GREAT EFFECT ON PEDAL FEEL.
The drum brakes (By brake standard) need 1/4 lines to be able to release quickly.


Disc brakes work better with the 3/16 line. 1/4 Larger lines can make a pedal feel spongy when used for disc brakes, that why it is recommended that the 1/4 factory front lines be changed to the 3/16 line.

Changing the master cylinder bore does not effect pressure rate. It changes flow rates. Same principle as the line size.

Flow rate is the factor on pedal feel. Along with pedal ratio.






Front lines are 3/16", rear is 1/4".


dc
This is the acceptable size.



From MP brakes. Technical support Disc Front rear drum
http://www.mpbrakes.com/technical-support/troubleshooting-disc-drum-05.cfm

Master cylinder piston diameter too small.
If the diameter of your master cylinder piston is smaller than required by wheel system volume requirements then you will experience a long pedal travel. Determine what the original master cylunder bore diameter was and replace the master if too small. Remember with an old vehicle the master could have been incorrectly replaced by a previous owner.
 

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Been down this road many times and I will not argue about it.

your dealing with pressure and flow rates.

The line size has a effect on flow rate! FLOW RATE HAS A GREAT EFFECT ON PEDAL FEEL.
The drum brakes (By brake standard) need 1/4 lines to be able to release quickly.


Disc brakes work better with the 3/16 line. 1/4 Larger lines can make a pedal feel spongy when used for disc brakes, that why it is recommended that the 1/4 factory front lines be changed to the 3/16 line.

Changing the master cylinder bore does not effect pressure rate. It changes flow rates. Same principle as the line size.

Flow rate is the factor on pedal feel. Along with pedal ratio.







This is the acceptable size.



From MP brakes. Technical support Disc Front rear drum
http://www.mpbrakes.com/technical-support/troubleshooting-disc-drum-05.cfm

Master cylinder piston diameter too small.
If the diameter of your master cylinder piston is smaller than required by wheel system volume requirements then you will experience a long pedal travel. Determine what the original master cylunder bore diameter was and replace the master if too small. Remember with an old vehicle the master could have been incorrectly replaced by a previous owner.
How much flow rate do you need to actuate brakes?
How about flow rate when brakes retract?
How does the MC bore size affect flow rate?
How far does the fluid travel?
Does brake fluid flow in two directions or circulate through the MC?
Is brake fluid compressible? If so, by how much?
Does the size of your caliper pistons or wheel cylinders affect braking force? How about flow rate?
What is the relationship between the size of your MC piston and your caliper pistons?
 

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Can't we just keep this thread tech related?
Why can't replys with information that may or may not be completely accurate be questioned? If I say use 3/4 inch lines and your problems will be fixed is wrong and someone points it out why are they called out to keep it technical. Seems less than accurate information could give someone a lot of grief chasing down the real problem.
 

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Why can't replys with information that may or may not be completely accurate be questioned? If I say use 3/4 inch lines and your problems will be fixed is wrong and someone points it out why are they called out to keep it technical. Seems less than accurate information could give someone a lot of grief chasing down the real problem.
I never said that people shouldn't question what they're being told. I just wanted to make sure that the replies are presenting technical info and not calling into question any personal, non-technical, attributes of the poster.

Some of the responses were getting personal rather than technical, that's all.
 

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I'm thinking I need to go to a master cylinder with an 1 1/8" bore - because I can't get enough fluid to fill up the rear wheel cylinders and those thru-frame fittings.


dc
I'm a little confused with this statement....

IF your lines are not full.. you have air...

if your rear brake servos are not actuating fully your shoes are not adjusted properly....
 

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Discussion Starter #18
Yes, the line size will not have any bearing on brake performance. The MC bore size will result in what was already mentioned with regard to pedal travel and effort. My question is what kind of proportioning valve are you running, and is it adjustable?
Prop valve is stock type, non-adjustable combination valve, setup for disc/drum (again purchased through Heidts with the MC).

have you checked the pedal ratio? with manuals you should be at around 6.0 and up....

as for Bore.. NOGO pegged it.. if anything you would be happier with a 7/8" to 15/16" bore

I would like to find a stock 7/8" bore GM 4wheel disk MC..for my 4wheel disk app. but alas.... they do not exist... that I know of...
Pedal ratio is stock; car came with manual brakes; brake pedal and rod were not changed, only the MC. I don't understand how a smaller MC will help, aren't we talking about a volume issue here, not pressure??

From MP brakes. Technical support Disc Front rear drum
http://www.mpbrakes.com/technical-su...sc-drum-05.cfm

Master cylinder piston diameter too small.
If the diameter of your master cylinder piston is smaller than required by wheel system volume requirements then you will experience a long pedal travel. Determine what the original master cylunder bore diameter was and replace the master if too small. Remember with an old vehicle the master could have been incorrectly replaced by a previous owner.
Thanks for the link. Remember, the size of the rear wheel cylinders is 15/16", only 1/16" smaller than the 1" MC bore, and I have those thru-frame fittings in front, which are probably 3/8", so it would seem to me that my particular problem is volume, not pressure..

Quote:
Originally Posted by dlc1979

I'm thinking I need to go to a master cylinder with an 1 1/8" bore - because I can't get enough fluid to fill up the rear wheel cylinders and those thru-frame fittings.


dc
I'm a little confused with this statement....

IF your lines are not full.. you have air...

if your rear brake servos are not actuating fully your shoes are not adjusted properly....
What I should have said here is I can't get enough fluid on a single pedal stroke to fill up the rear wheel cylinders and those thru-frame fittings. Remember, brakes are working, pedal is just too low for my taste (almost on the floor).


Quote:
Originally Posted by wskaiser
Why can't replys with information that may or may not be completely accurate be questioned? If I say use 3/4 inch lines and your problems will be fixed is wrong and someone points it out why are they called out to keep it technical. Seems less than accurate information could give someone a lot of grief chasing down the real problem.
I never said that people shouldn't question what they're being told. I just wanted to make sure that the replies are presenting technical info and not calling into question any personal, non-technical, attributes of the poster.

Some of the responses were getting personal rather than technical, that's all.
We're having fun now....:D. Seriously, I appreciate all the comments and thoughts.

I have a mopar unit, 1 1/32" bore, aluminum casting/plastic resorvoir... very lightweight and works very well on my disc/drum setup.
Available at any auto parts store, new or reman, about 30-$50. Mid 80's full size rear drive cars.
Will need to elongate mounting holes slightly to fit studs.
I believe that '69 Chevelle SS's used a 1 1/8" MC that will bolt in and looks period correct.

My race car buddy uses the same Mopar MC for his '55 Chev 4-wheel disc setup and it works well for him.

dc
 

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Thanks for the link. Remember, the size of the rear wheel cylinders is 15/16", only 1/16" smaller than the 1" MC bore, and I have those thru-frame fittings in front, which are probably 3/8", so it would seem to me that my particular problem is volume, not pressure.
Your fluid volume will not change. The ratio of MC to piston determines input vs. output force as well as displacement (distance traveled).

What I should have said here is I can't get enough fluid on a single pedal stroke to fill up the rear wheel cylinders and those thru-frame fittings. Remember, brakes are working, pedal is just too low for my taste (almost on the floor).
If your brake components are not full of brake fluid you have air in the system. This is a closed hydraulic system not a flow through system (as some seem to think). If you pump your pedal quickly does your pedal travel start to decrease? The only way to know that fluid has not filled your components is from trapped air. Try bleeding the brakes again.
 

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Discussion Starter #20
Your fluid volume will not change. The ratio of MC to piston determines input vs. output force as well as displacement (distance traveled).

If your brake components are not full of brake fluid you have air in the system. This is a closed hydraulic system not a flow through system (as some seem to think). If you pump your pedal quickly does your pedal travel start to decrease? The only way to know that fluid has not filled your components is from trapped air. Try bleeding the brakes again.
I'll re-bleed and I'll post the results. Thanks a bunch.
 
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