Technical Ford juice brakes - Problem, help needed!

You are correct, however Volume and Pressure are two different things. An early Ford master is 1-1/6" bore, it clearly will move more Volume than a 7/8" bore like the Mustang. That's what is missing and why he has good brakes after a second pump. He finally moved enough Volume to apply the brakes.
The Wizzard

 

I'm no expert, but after the lines are bled, isn't there a continuous stream of fluid through out the system, including full wheel cylinders? If that is true, then the WC is already full, no? So volume wouldn't be an issue.

Sorry if I just confused the issue more, just trying to make sense of it all.

 

The comment above about pushing thwe wheel cylinders in with your fingers, and ruining them, once you intsall the cylinder, put shoes in place and put the spring on, the piston gets pushed all of the way in, seems that would be same as your fingers, piston goes in dry the, you push fluid and bleed.
Is there another way?

 

Yes, that makes sense. I don't know the specifics, but my pops as well as many other Hotrodders have told me not to mess with the wheel cylinders, it will ruin the seals. Urban legend? Could be.

 

I've taken a bazillion (OK, maybe a few hundred) wheel cylinders apart and never ruined the seals. The only thing I can think of that may do damage is a burr on the fluid inlet passage, but final honing during manufacture should have removed any.
Urban legend, along with others brake-related.

 

It's simple Physics. Think this way. It takes longer to pass 1 Gallon of fluid through a 1/2" hole than it does through a 1" hole using the same pressure pushing it through. Small bore master can create the same Pressure as a large bore master but takes longer to move the same Volume of fluid. You need the volume to move the wheel cyl its said distance as well as the Pressure.
The Wizzard

 

I think what they are saying about volume is: Imagine trying to squeeze one wheel cylinder and moving the piston in the master cylinder all the way. Not enough fluid volume. The volume to expand all wheel cylinders must be available from the master cylinder with less than one full stroke. Another part of the discussion is about pressure.

 

I think you are the mistaken one. How can something being pushed by a spring from the outside draw air past the object being pushed by the spring? It would have to be a vacuum to draw air past the cups. Brake shoes returning would not cause a vacuum by pushing the cups in. If anything, and the cups are sloppy enough, the resistance of the brake fluid combined with the strong spring force would push fluid past the cups.

I would first bench bleed the Master Cyl. Then make sure the shoes are adjusted out properly to keep them from returning too far causing excess travel when the pedal is pressed. Then bleed each wheel again. Should firm up the pedal real good.

If the Master is lower than the wheel cylinders you may need residual valves in the circuits.

**Edit**
MC bore diameter would also be an issue. I used a 1 1/8" Wilwood dual circuit MC for my brakes and I am lucky if the pedal moves an inch of travel.

 

Back to the original posters problem, double pumping to get a solid pedal. Well if you are a member two pump chump club then the issue is with too small a master cylinder. Not the size of the lines.

 

What is the benifit? The bleeder still has to be opened and closed so why not just make the bleeder have the provision for hose attachment built in? Sorta like stock bleeder?

 

""pump chump club""

Thats cute dick...If the OP is using a 67' or so Mustang MC then it should be one for drum/drum [a low end model] and it will have RV in both ports..Or should have..The brass block [just a note] plumbed in after the mc is just a distribution/warning light block and has no brake performance function..If I have read right in the past the ford [41'] MC would have been 1-1/16 bore so even if the mustang MC bore is as small as 7/8 it should be ok as when going from a single to a tandem the stroke ends up reduced so a smaller MC will just bring the stroke back at the pedal..Since the OP did not state that he had no brakes on first pump but it would pump up and stated that the pedal will hold for a length of time makes me have the opinion that the mc is bad in either piston or RV but I would lean towards the RV (s) leaking down and any "play" that the 10# took up reappears........

 

Their was a reason for the large bore of the MC,the system needed the volume. Why would you change that,brakes don't do well mix & match!

 

Wow, here we are Batteling it out trying to help a F.N.G. solve his problems and he hasn't even bothered to check back in to see if anyone has responded and he has logged back since posting the question. Almost feels like we were set up just to Piss back and Forth. I did a search and found 19 pages of same type of Question and conversation. W.T.F?
The Wizzard

 

Looks like I just jumped on at the right time, you guys sure don't give a guy a chance to try any of the suggestions before you accuse someone of wasting your time. I've logged on each day to check this posting but didn't want to add anything until I actually had something to report. Sorry if I offended anyone by not replying. I really appreciate all of the suggestions and tips, there are so many and I've written a list of all the possibilities and will work through them until I can pin point what exactly the issue is. I'll jump back on and report back how I go as I work through the list of suggestions as to what the problem may be.


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I'm running 40 brakes, and a 67 Mustang master, and I have excellent brakes, and a very firm pedal.

The master cylinder starting leaking so I replaced it, and I had the same situation as you describe, after replacing the master.

What led me to the solution was the fact that I had good brakes after I pumped them, but once the pedal was released, I had to pump again.

If I maintained slight pedal pressure, after pumping the first time, it was fine.

I adjusted the push rod, making it longer by only about and 1/8 inch, and all was well again.

Please try this before anything else.

A 67 mustang master and 40 brakes should work quite well, they do for me.

Rich

 

SEBFontana, From the original post, you have to assume that the poster has correctly adjusted the pedal and bled the unit. Next it's called math class, I slept thru most of it, but the part of the reason that the brake system doesnt work correctly is that the master cylinder is too small to displace the fluid to fill the wheel cylinders. Volume displacement can be figured by determining the volume of the cylinder and the stroke. V=3.14 x r2 x stroke.
example:
A 7/8 wheel cylinder with a 1/2" stroke displaces .297 cu in fluid
A 1-1/16 wheel cylinder with a 1/2" stroke displaces .397 cu in of fluid or .100 cu in more fluid.


By computing the volume necessary to expand the wheel cylinders to lock you can determine the size of the MC or the stroke necessary to have adequate fluid transfer for braking.


Or the easy way, you can look up the size of the master cylinder that was used to operate the donor brakes and match it up to the size you need to have for your installation.

So the issue, is there enough pedal stroke because its limited with a homemade pedal ratio or is the master cylinder too small for the application?

 

The only waste of time here is when people tell you to do something they have only read about and not actually done. I personally am not Offended however some kind of interaction let's us know your listening. Enough said there. Good brakes are a proven method no matter what parts your using. One guys "Good enough" is anothers "Holly Shit"
You need to know the Hot Rod industry is built on selling parts, not always what you need. Master Power is the worst at this. Why would anyone buy a New master for Disc brakes then Add residual valves to it when you can buy a master with them already installed? The after market industry does very well when you don't know any better. You have one small problem and all the info needed to correct it. What will your choice be? I have a grate deal or respect for Dick Spadaro and his input. He like a very Few others here will speak from experiance not hit and miss. I personally won't advise unless I have done it and things worked properly, not just kind of OK.
The Wizzard

 

Dick, math I stayed awake in class cause the teacher had this ruler and I sat in the front row..!!..Now I know you mean MC's,

""example:
A 7/8 wheel cylinder with a 1/2" stroke displaces .297 cu in fluid
A 1-1/16 wheel cylinder with a 1/2" stroke displaces .397 cu in of fluid or .100 cu in more fluid.""

Yes, your example above is true to the word, if they are both single pot as in OEM 41' or so Ford style..Now make the 7/8 MC a tandem; doesn't each piston move 1/2" ? I can not see how it would not be, maybe a little stroke loss for port closing but should be close to .297 volumn at each port, .594 total or only have to stroke about 3/8" to equal the out put of a single 1-1/16 MC at 1/2" stroke....At least thats how I figure it..

 

Seb, I told you I slept thru math and again got smacked with the rule. I broke it down to a two system to single system comparison and the dual out pushed the single as you profess. I go between antique cars and hot rods so much I have to remember what I'm working on.

Since we havent heard from the OP on what size his MC is this would lead me now to the question the pedal ratio for displacement or the simple adjustment of not having the upper backing plate stops clocked correctly when the brakes were first adjusted. this simple adjustment could cause a double pump issue.

Question to the original OP. What year backing plates do you have, there are different adjustment procedures between 39-41 and 42-48.

Did you clock adjust the hex nuts at the top of the backing plates so the brake shoe locked on the drum when you adjusted the brakes or did you roll them all the way in to the stop position, so you can hear no drag. The hex nuts at the top of the backing plate are stops to prevent the spring from fully returning the shoes in the wheel cylinder travel thus keeping the shoes close to the drum surface.

When adjusting the brakes the hex nuts should be rotated outward so the shoes are tight to the drum, this positions the brake shoe and wheel cylinder correctly during brake bleeding. The hex bolts are rotated to lock the shoe to the drum and the brakes are then bled. After the brakes are bled, the hex nuts are evenly rolled inward until the drum turns free on the shoe with only a slight whisper of drag. Return each side hex evenly one flat for one flat to ensure that the shoes remain centered.

If you dont do it this way and the hex bolts are at full rest position each time you push on the brakes the shoes expand only a pedal travel distance. If you have positioned the hex at the rest position the springs pressure retracts the shoes further than necessary from the drums. The next time you need to apply the brakes the shoes are too far away in the initial pedal travel that it requires an additional pump to get the shoes to hit. If you have 39-42 backing plates its a little more elaborate but you can get the same problem.

 

Hi Dick, I plan on going through your instructions on the car over the next couple of days as my first step. I will adjust each drum as per your instruction and bleed the system again then will see what happens. Thanks for all of the detail, it will make it much easier. Im not sure what year backing plates i have. Is there a quick way to tell? Sorry, its my first build.I will also check the size of the MC, I was told it was a mustang MC which I had rebuilt. I'm not sure what year mustang though. Thanks again.


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I'm not getting into theory, but suffice to say I had exactly the same components and the same problem. I installed a 10lb rpv in each line and the problem was solved. I dont know why, or how, I just know it worked. That's enough for me.

 

I am having a similar problem with my 64 ford drums. Low pedal that I feel I need to either cram to within an inch of the floor or pump a couple times to get stopped.

Unlike the OP I do have 10lb residual valves inline from the MC, and I am still not getting a good pedal. I even brought it to a shop and had them bleed them thinking I hadn't done a good enough job myself.

After reading all of your theories I am at a loss too. My 67 ford MC has a 1" bore as did the original single pot I took out?

This guy seems new to brakes, and so am I, could it be in the assembly of the drums themselves, like maybe we have the springs on backwards? I think the springs are rated differently judging by the size of the beehives?
Is that even possible? Because the shoes are different sizes?

 

if your master cyl. is lower you should run residual valves because the shoe springs are pushing fluid back in the mc. residuals are a one way and hold 10 or 2 #of pressure

 

Did you adjust the shoes against the drums? I was taught to tighten the star wheels or adjusters (thru the slots in bottom of backing plate) til the wheel would not roll and then a little more. I was told this centers the shoes. Then back off til there is just a little drag on the drum. If there is a tighter spot when you roll the wheel, try the tighten til it won't roll deal again, then loosen to slight drag. Adjust all four.

If this adjustment does not solve your problem, try bleeding the master cylinder. You may be able to crack one line fitting at a time while someone slowly pushes the pedal, tightening when there are no bubbles. The real way to do it is to screw short pieces of brake line into M/C that bend up into the fluid well. Pump cylinder slowly til no more bubbles come out of short lines.

 

Yes there is a reason for the springs to be different or they wouldn't bother to do so. Pretty sure it has to do with rotation of drum, i.e., one side opposite the other..Your MC selection and application match well enough..Post #49, per Dick S, tells adjustment proceedure of early Ford brakes gave me an Idea that any brake bleeding could be done by locking the wheels with the adjusters [if you can/have at them] thus eliminating any play and if you get good pedal then once backing off the adjusters the pedal should still be good, if not then there is something a miss in the brake assemblys ..

 

Hi all, I haven't had much time to work on the pickup but I finally got a couple of days together to spend on it and I readjusted the brakes, then bled the system again and this didn't solve the issue. So I then installed the residual pressure valves in each line as close as I could to the MC. I then bled the system once more and this has fixed the issue. The RPV's have fixed it.
Thanks to everyone for their tips and help, there is no way I could have solved this without your knowledge. Thanks again!


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Thanks for posting final solution..

 

Looks like the springs in the drums where strong enough to squish the brake cylinders and push the fluid back into the master cylinder.

Did you use a drum drum / disc disc or disc drum master cylinder.

cheers Julian

 

Do they make residuals that screw directly into the m/c?

 

Not that I have seen but there are fittings that can be used..Found them at Pep boys but I am sure NAPA or other auto stores would have them..