Bleeding brakes-pedal pressure problem. Could use some advice/suggestions

acchaplin said:
Another one of those videos said that the smaller MC bore, the more pressure, the bigger the MC bore the more volume. Didn't know that. They used a math formula to figure of which MC bore to the pedal ratio to use. All that math 'siphern is way above my 6 remaining "brain cells." I can do fractions in my head, but that is it.
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I'd like to take a look at that video. Please post the link.

Regarding volumes and pressures:

The parameters are somewhat fixed:

- Brake lever ration which is 3.85 for you
- Leg force to apply brakes. Of course this is variable but figure on 100 LBS force.

The above two fixed variables will give you a brake line pressure that depends on the internal diameter of the MC.

Pressure = Force/Area psi
Area = Pi X (Diameter/2)**2
F = 100lbs X 3.85 (pedal arm ratio)

P = (100 Lbs) X 3.85 / (1.00/2)** X 3.1416 = 490psi

So ... , the way to get higher pressure is to increase the pedal arm ratio or decrease the internal diameter of the MC, or more leg force :-)

A larger diameter MC will push more brake fluid volume at the cost of decreasing the brake line psi with a smaller stroke of the brake pedal.
A smaller MC diameter will give you more pressure but also more stroke which is not the greatest for modified '32s.

I use a stepped bore MC, https://www.fordbarn.com/forum/showthread.php?t=315565&highlight=bore+cylinder&showall=1

Glenn
 
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glennpm said:
Please unscrew the fitting to your MC and see what you have before doing anything else. Ten minute job, well 1/2 hour to gather a drain pan, drill bit and wrench :-)
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Ok, Just got done checking. VERY tiny drill bit + a paperclip. They both go into the flaired port hole about 3/4". The threads, flared portion of the port, and the MC casting looks to be all one piece. Just like your picture with the paperclip.

So that means my "Buzzard Puke Green" colored MC does not have any residual valves.

I have sent out a couple of PM's asking if one happens to have a loose '32 brake pedal laying around, to get the measurement from the cunter hole where the pedal foot pad bolts into to the center hole of the pivot point. I do not want to dissamble the floor boards, wireing harness, switches, and a dozen other things, take a chance of loosing the original brake pdeal "squeak" sound, just to get one measurememt, when I can get that measurement much easier from someone who can measure a loose part right in front of them. Soon as i get that measurement, I'll post it on here.
 
acchaplin said:
Ok, Just got done checking. VERY tiny drill bit + a paperclip. They both go into the flaired port hole about 3/4". The threads, flared portion of the port, and the MC casting looks to be all one piece. Just like your picture with the paperclip.

So that means my "Buzzard Puke Green" colored MC does not have any residual valves.

I have sent out a couple of PM's asking if one happens to have a loose '32 brake pedal laying around, to get the measurement from the cunter hole where the pedal foot pad bolts into to the center hole of the pivot point. I do not want to dissamble the floor boards, wireing harness, switches, and a dozen other things, take a chance of loosing the original brake pdeal "squeak" sound, just to get one measurememt, when I can get that measurement much easier from someone who can measure a loose part right in front of them. Soon as i get that measurement, I'll post it on here.
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You should have gotten resistance right away with your probes, so no RPVs. If the flared portion is machined into the casting, no RPVs. The ones that have them would have a brass insert.


I think the fusia red RPVs will be a nice focal enhancement to your bile green MC :-)


I posted the 13" arm length in post #59.


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rich b said:
I would avoid the multiple Chineseum valve listings on eBay and instead get either the USA made residuals from SS Brakes or Wilwood valves from Speedway Motors. We have had good luck with both.

Have had trouble with 1/8 NPT threads in the cheapo valves a couple times; they seem off and tend to want to leak up until the point of the aluminum body cracking.
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Thanks for the suggestions!

I was wondering if those "loom-num" (WV talk for aluminum) valves would even work for me! See, aluminum and stainless don't get along together. Trying to thread a stainless tubing nut into aluminum threads lible to gauld up 1/2 way in.
 
acchaplin said:
Thanks for the suggestions!

I was wondering if those "loom-num" (WV talk for aluminum) valves would even work for me! See, aluminum and stainless don't get along together. Trying to thread a stainless tubing nut into aluminum threads lible to gauld up 1/2 way in.
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I hear you on the galling, so use regular steel fittings at the RPVs. Wet them with brake fluid and you should be fine with those loom-nums!
 
glennpm said:
I have a '32 and from the center of the shaft to the pedal mounting bolt is 13"


So for you: 13"/3.375 = 3.85 ratio


(My ratio is 13/3 = 4.33)


Almost all hydraulic converted systems for '32s will have similar ratios since the MC pushrods are below the K member.
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I just a little bit ago sent out a couple of PM's asking if one would have a brake peadal laying around to get the top measurement from. My front floor board is in and all hooded up. Too much trouble to remove it for one measurement.

You are ahead of me. THANKS
 
glennpm said:
I'd like to take a look at that video. Please post the link.

Regarding volumes and pressures:

The parameters are somewhat fixed:

- Brake lever ration which is 3.85 for you
- Leg force to apply brakes. Of course this is variable but figure on 100 LBS force.

The above two fixed variables will give you a brake line pressure that depends on the internal diameter of the MC.

Pressure = Force/Area psi
Area = Pi X (Diameter/2)**2
F = 100lbs X 3.85 (pedal arm ratio)

P = (100 Lbs) X 3.85 / (1.00/2)** X 3.1416 = 490psi

So ... , the way to get higher pressure is to increase the pedal arm ratio or decrease the internal diameter of the MC, or more leg force :-)

A larger diameter MC will push more brake fluid volume at the cost of decreasing the brake line psi with a smaller stroke of the brake pedal.
A smaller MC diameter will give you more pressure but also more stroke which is not the greatest for modified '32s.

I use a stepped bore MC, https://www.fordbarn.com/forum/showthread.php?t=315565&highlight=bore+cylinder&showall=1

Glenn
Click to expand...

Oh feces! My 'brane' just exploded and went into 'lockdown'! Now my eyes are locked in crossed. I get VERY confused when trying to read math forumlas. Anything past gradeshool level (except for fractions) adding, dividing, I can't comprehend.

If I have to now understand math, gemotery forumlas to get brakes to work on this car. I'll just quit now (save on the migrane pain) and try to trade the '32 for a nice running/driving '50 Chevy Convt.

THANKS for your help Glenn!
 
So ... , the way to get higher pressure is to increase the pedal arm ratio or decrease the internal diameter of the MC, or more leg force :-)

A larger diameter MC will push more brake fluid volume at the cost of decreasing the brake line psi with a smaller stroke of the brake pedal.
A smaller MC diameter will give you more pressure but also more stroke which is not the greatest for modified '32s.

I have read, re-read your above statement so many times, my hair is starting to hurt. It's like trying to read through a fog that keeps moving. I almost get to the point of fully understanding, and then it all goes fuzzy. I wonder if you re-worded your three statements,,,,,,,, or if someone else explain (in their words) your above statement. That I might be able to understand.

What I am getting, is that it will take (maybe) more leg pressure. (than I might be able to do) or make the bottom of the pedal length longer.
A larger diameter MC will operate the wheel clys, but the line ID is too small to handle the volumn of fluid. So that won't work.
A smaller diameter MC will get the pressure that is required to operate wheel clys, but the pedal will go to the floor doing it. So that won't work.

With what I have in my set up right now. Line ID, pedal ratio, wheel clys, etc. "If" I am to get another MC that has the residual valves incorporated into the line ports. Do I get a 1 1/16" bore, or a 15/16" bore? (or do they even make those bore sizes?)
 
To add more—- the stroke of the rod pushing the master cylinder has to move the piston its full stroke too —- has to push it far enough for the primary piston to make contact with the secondary piston and move it enough to apply the brakes it services.
Perhaps put the pedal “on the floor “ and remove the clevis pin ( bleeder. screws open so no hydraulic pressure) then push on master cylinder rod to see if maximum pedal applied also results in a full stroke of the master cylinder.
 
Kurt in NJ said:
To add more—- the stroke of the rod pushing the master cylinder has to move the piston its full stroke too —- has to push it far enough for the primary piston to make contact with the secondary piston and move it enough to apply the brakes it services.
Perhaps put the pedal “on the floor “ and remove the clevis pin ( bleeder. screws open so no hydraulic pressure) then push on master cylinder rod to see if maximum pedal applied also results in a full stroke of the master cylinder.
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Yes I did something like that procedure when I made the rod from the pedal to the MC.
 
Normal manual pedal ratios are in the 6-7:1 range, while power assist ratios are 3-4:1. You are working with the wrong ratio, so first, correct the ratio before any other alterations, by shortening the distance between the pedal mount and push rod close to 2".
 
Okay, summary time for me.

- Your 1"-1" dual master is fine.
- Stock Ford of this first Ford use of hydraulics had a single MC with a 1-1/16" bore
- There is no need to change your stock wheel cylinders. Ford has already figured that out, including providing larger wheel cylinder bores for the leading, dominate brake shoe.
- There is no need to check the stroke. With a brake arm ratio of 3.85, you will have more stroke than stock, noting that a '40 has a ratio of 6 to 1.

I recommend that you do the following:

- Keep everything as you have it but install two inline RPVs as shown below. Your leg length for the rear may be too short to allow the flaring tool. You can either make that leg longer or put the RPV on the straight hard line on your torque tube right after the flex hose. That's what I have.

When you buy the RPVs, get them without fittings. You'll have to buy four 1/8" NPT X [FONT=&quot]7/16-24 inverted flare. Most of the kits will have a [/FONT][FONT=&quot]3/8-24 which is for 3/16" lines.[/FONT]
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Glenn
 
V8 Bob said:
Normal manual pedal ratios are in the 6-7:1 range, while power assist ratios are 3-4:1. You are working with the wrong ratio, so first, correct the ratio before any other alterations, by shortening the distance between the pedal mount and push rod close to 2".
Click to expand...

The way the MC relocation kit is made. The pedal rod is level from the bottom of the brake pedal into the MC. The rod is VERY close to rubbing the bottom of the frame now. I don't know if you can see it in the picture I posted, or not.

I am not familiar with what different MC relocation kits are offered. This kit was reccomended to me.
 
Everyone has neglected to question if the drums are cut out of speck(over cut to smoothen out) you will never get a good pedal! how much over were they cut? I believe this could be your problem.
 
acchaplin said:
The way the MC relocation kit is made. The pedal rod is level from the bottom of the brake pedal into the MC. The rod is VERY close to rubbing the bottom of the frame now. I don't know if you can see it in the picture I posted, or not.

I am not familiar with what different MC relocation kits are offered. This kit was reccomended to me.
Click to expand...


A correct kit would have/should have retained the manual 6:1 or so ratio. Best to modify what you have, or fabricate up a new bracket that allows correct ratio and master cylinder placement.


Below is what's on my '32. Very simple angle iron and brace. (I installed a C.E. X member to the ASC '32 rails.)
 

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V8 Bob said:
A correct kit would have/should have retained the manual 6:1 or so ratio. Best to modify what you have, or fabricate up a new bracket that allows correct ratio and master cylinder placement.

Below is what's on my '32. Very simple angle iron and brace. (I installed a C.E. X member to the ASC '32 rails.)
Click to expand...


With all due respect, acchaplin has an arrangement that is very typical for stock '32s with hydraulic brakes and it does work even with the less effective arm ratio. This thread started with a problem bleeding and getting a hard pedal.


Are other designs out there? Sure some use a bell crank and others modify the mechanical brake shaft on the back of the K-member.


*******************


That aside, when I set mine up I considered drilling a large hole through the back of the pedal bracket and frame. I even drilled a hole in the new lever arm I welded to the stock '32. I decided against this route, keeping the frame as stock as possible using existing bolt holes.


Food for thought AFTER you get what you have working. Pics are of my car. One down side is the MC fill cap will be close to the wood floor and I think only fillable with a floor cutout from above.



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Sometimes,....adding common and important safety upgrades to an original chassis may require very slight modifications, like drilling a hole or two. The car is already non-stock, so where do you draw the line?
 
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