Brake booster vacuum port

[56Alan]

Just finished a rusty hope disc conversion using the original rebuilt MC and am disappointed with the amount of pedal pressure required to operate the brakes. I intend to change to a dual mustang or similar MC and am thinking of fitting a brake booster as well. My question is has anyone fitted a booster to a standard flathead 6? and if so where do you take the vacuum from?

[greg g]

you could T off the fitting for the windshield wiper motor.  That port should supply am accumulator as well as the wipers.  Or you could feed your accumulator and pull off a line to power the  wipers and not have to worry about low vacuum stalling your wipers up hills.

[DJ194950]

What is the inside diameter of the master cylinder bore. Some have tried 1" and 1/16", 1 1/8" with disc  brake and had what you are experiencing. Low brake pressure and excess pedal pressure required.

You could try a smaller diameter bore size, something like a 7/8" or 15/16" bore. That would make more pedal travel but higher brake line pressures the smaller you go.

 

Another approach ??

 

50HR

[56Alan]

I have the standard mc which is over 1" diameter and the pedal is already low and as I understand it as you say a smaller mc diameter is required to increase pressure to the discs also I think more fluid volume is required which is my thinking behind changing to a dual mc from a mustang or similar. I was hoping someone had fitted a brake booster to a flathead 6 to prove it will work, that way I could be confident of the car stopping when my wife drives it.

[greg g]

How does a dual reservoir provide more fluid volume or pressure? I believe the dual reservoir is to provide for separate supply of fluid to front and rear brakes, or some systems split the brake fluid diagonally. This provides a measure of safety if one set of brakes should somehow loose fluid, allowing for partial braking instead of complete failure.  Where is the advantage of the dual system to provide, shorter stroke or firmer pedal?  Seems to me you need to research how much volume is needed and how much is provided by the MC.  Simply mixing and matching seems like chasing your tail.  I would start by identifying the calipers you are using and matching MC, hoses, and metering valves to them. 

[56Alan]

Correct me if I am wrong but a dual mc has a double piston and two fluid chambers so there must be twice the volume available unlike the original mc. Also calipers require more fluid and at a higher pressure. My thinking behind a mustang mc is that I believe ECI brakes use this on their disc/drum conversion kit but as you say I am still researching.

[Niel Hoback]

The volume of fluid available to each piston, being separated, is about the same as the a single reservoir has for one piston.

Disc calipers require less fluid to apply pressure than drum cylinders. Disc pistons do not pull back from the caliper like drum cylinders do because there are no springs pulling the piston back away from the pads. Piston movement in a disc cylinder can be measured in thousands of on inch, small enough that fluid doesn't really move, the pressure increases.

Dual MC's use a spring between the primary, ( rear wheels), and secondary, ( front wheels),  pistons . Pressure is applied to the rear wheels first, after a preset pedal pressure is reached, the spring between the pistons collapses and the front piston begins to apply pressure, Pedal travel includes the distance between the two pistons in the MC regardless of the distance between the shoes, pads and rotors and drums.

Pedal travel should be about the same with a single or double reservoir if the MC bore diameter is the same.

[William Davey]

On 9/9/2016 at 4:20 AM, 56Alan said:

Just finished a rusty hope disc conversion using the original rebuilt MC and am disappointed with the amount of pedal pressure required to operate the brakes. I intend to change to a dual mustang or similar MC and am thinking of fitting a brake booster as well. My question is has anyone fitted a booster to a standard flathead 6? and if so where do you take the vacuum from?

Have you contacted Charlie about your pedal pressure?  I found his service after the sale to be outstanding and in my case the brakes work very well with only light pedal pressure.  Different vehicle I know, but stock (new) master cylinder and the rustyhope kit.

[56Alan]

I did contact charlie and his comment was "even a standard rebuilt mc is next to useless on this set up" I decided to keep the original mc as I had read on here that this set up worked ok. The only thing I think that may be causing my low pedal is air still in the system but the pedal doesn't pump up. Is your set up a disc/drum with single line mc?

[Dave72dt]

Nothing to do with pressure but as for low pedal, check the distance or gap between the plunger and the mc piston.  Mc piston has to come all the way back so the plunger cannot push against it at all when at rest.  Too great a gap will cause a low pedal so the closer you get it without applying pressure against the piston, the higher the pedal will be.  Early production disc brakes without power tended to require more effort from the driver than drum brakes did, as I recall, so boosted disc became the norm.  I don't think the early Mustang discs were boosted units either, but don't quote me on that.  Some may have been.

[dale]

Speedway Motors has a frame mounted dual master cyl. with attached booster including the pedal.

[Jeff Balazs]

I fitted a M/C from a Grand Cherokee and changed out all the lines and hoses to 3/16". I did not fit a booster and at first thought the required pedal pressure was excessive. It took a few adjustments to the linkage and the adjustable proportioning valve and then some miles...... but now it feels great. No booster needed.

Hth, Jeff

[William Davey]

14 hours ago, 56Alan said:

I did contact charlie and his comment was "even a standard rebuilt mc is next to useless on this set up" I decided to keep the original mc as I had read on here that this set up worked ok. The only thing I think that may be causing my low pedal is air still in the system but the pedal doesn't pump up. Is your set up a disc/drum with single line mc?

Alan, my truck is disc front from Charlie and stock drum rear rebuilt. New NAPA master cylinder and all new brake lines and hoses. Hope this helps.

[56Alan]

Hi Jeff, thanks for the reply. I am trying to get away without having to fit a brake booster much like your own set up providing it works ok. With my 48 Plymouth the front of the mc holds the spindle that the pedals pivot on and in order to keep this some people have removed the guts of the mc and fitted a dual mc behind and extending the push rod so it passes through the old mc. Is your truck like this? and what year is the jeep mc you used?

[Jeff Balazs]

Alan;

No the trucks have a different bell housing mounted arrangement. I think a late 90's Cherokee M/C for front disc & rear drums model would probably work best. There are lot's of threads here on the topic. Seems to me some I have read mentioned the attachment arrangement you mention.

One thing I would have to say is if your lines and hoses are old you should probably replace them while you are doing this.

Jeff

[56Alan]

Thank's for all the advice, now all I have to do is decide which way to go next!