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Master Cylinder question....

Discussion in 'The Hokey Ass Message Board' started by adavis, Jun 16, 2009.

  1. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    The brakes on my 1927 Model T aren't anywhere near what they should be, and after trying different things I'm turning to the HAMB for advice. I'm using a plain jane mid-60's Ford dual master cylinder mounted under the floorboard. I have 10 psi residual valves front and rear and am running 12" buick drums on the front and 10" Ford drums out back. I've bled the system and checked for leaks but the brakes just aren't anywhere near what they should be. My thought is that I have the front and rear brakes backwards on the master cylinder. The reservoirs are the same size, but the port from the reservoir farthest from the mounting flange is larger than the other. I assumed that the larger port meant it was for the front axle, but after looking at the cheap mc from Speedway I'm not sure. The Speedway mc has the front brake line on the reservoir closest to the mounting flange, but both ports are the same size. The mc I have is for a mid-60's ford with drums front and rear. Anyone have a suggestion before I switch the front and rear lines on the mc? Thanks.:confused:
     
  2. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    Switching the lines shouldn't make a difference. Do you know what your pedal ratio is? I'm pretty sure it should be around 6:1 on a manual brake setup.
     
  3. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    Stupid question....but how do I calculate my pedal ratio? Also, why won't it make a difference if I switch the lines. I thought that a dual master cylinder had different proportions front and rear, hence the different fitting sizes for each reservoir.
     
  4. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    The pedal ratio would be in relation to the distances from the center pivot to either end, being the pedal pad and master cylinder push rod, assuming you have an under floor mounted master. If you push the pedal pad 6" the push rod end should move 1". As far as the lines go, the pistons are the same size front and rear so swapping them would make no difference in pressure. As far as I know the main reason for different size fittings would be to make sure the lines would be connected properly for a disc/drum application or in the belief that the rear brakes would apply slightly sooner when connected to the rear because that end would see movement first. By the way, Is your pedal soft or do the brakes just not seem to grab enough?
     

  5. Billet
    Joined: Oct 13, 2008
    Posts: 275

    Billet
    Member

    Oh the humanity, The front reservoir is the back and the rear is for the front brakes. You didn't list why the brakes suck- too little braking- soft pedal- spongy? How about your wheel cylinder sizes front and rear? When rocks were soft OEM's adjusted brake bias on drum/drum setups by using different size wheel cylinders. Here is a thread that might help (http://www.hotrodheaven.com/tech/brakes/brakes3.htm)
    Choosing the "right" braking system components can be difficult at best or at worst dangerous and can take all the fun out of driving your car.
    Good luck
     
  6. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    OK, so I think my pedal is pretty close to the 6:1 ratio. I made the pedal arm and it is connected to a shaft that runs through the frame. On the opposite side of the frame is a lever arm that is attached to the mc pushrod. The brake pedal doesn't really feel soft. The brakes just don't stop the car as they should. I mean I'm using factory 1961 Buick brakes in front (huge 12" drums with 2" wide shoes) on a car that MAYBE weighs 2000 lbs. I would think the car would stand on its nose when you stand on the brake. I've only gotten the back brakes to lock up by standing on the brake, and the car just slows to a stop when normal pressure is applied.

    I'm curious about the Speedway mc, because my buddy has it and we can clearly read "front" and "rear" on the two ports, with the "rear" being on the port farthest from the flange. Could it be that the piston in the mc creates pressure on the closest reservoir first (ie the front brakes) and then the rear brakes as you press harder? Am I wrong to expect to be able to lock the front brakes up too?
     
  7. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    Billet,
    I'm using the factory Buick 12" brakes, wheel cylinders and all, on the fronts and the factory Ford 10" brakes that were on my 9" on the rear. I haven't changed wheel cylinders, but I wouldn't think I'd need to because I'm using front brakes for a 5000 lb. car on the front and rear brakes from a pickup on the rear. I can see if I was using a rear brake setup on the front or vice versa why I might have problems, but the components I'm using are where they were designed to be used except for on a car that weighs less than half.....hence my expectation of having really good braking.
     
  8. 39 All Ford
    Joined: Sep 15, 2008
    Posts: 1,531

    39 All Ford
    Member
    from Benton AR

    Still, we need to know THE PROBLEM with the brakes in order to really attempt at a solution...

    Pedal too hard?
    Pedal too soft?

    Could be a leverage issue..
    Could be a hydraulic issue..
    Could be an issue with the brakes themself...
    Maybe you have the brakes on the wrong side of the car......

    We need info...
     
  9. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    Ok, so what I'm dealing with is brakes that just slow the car to a stop, not really stop it. I can get the back to lock up if I stand on it, but the fronts never really stop.
    I've bled the brakes and can hear each cylinder working the shoes in each drum so I know each brake is doing something.
    The pedal is not soft. As I push it it get harder and eventually won't go any further (not because it hits the floor, either). If I pump the brakes twice quickly when I want to stop they work better.
    Would it help if I took some pictures of the pedal assembly?
     
  10. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    Is there any chance the piston is bottoming out in the master cylinder? I'm thinking it might be, being that it seems to work better when you pump it.
     
  11. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    Also, do you have external residual valves and if so, have you checked to see if they might be clogged or installed in the wrong direction?
     
  12. jagfxr1949
    Joined: Jun 27, 2008
    Posts: 277

    jagfxr1949
    Member

    It is possible that the master cylinder is internally bypassing and bottoming one or the other of the pistons - sort of sounds like that to me.
     
  13. If no-one's mentioned this....See if your wheel cylinders are the same diameter as the ones that went with that master cylinder
     
  14. Solidaxel
    Joined: Feb 21, 2007
    Posts: 233

    Solidaxel
    Member

    Are the shoes new, and have they been arc'ed to the drum?
    What size is the ID of the M/C?
     
  15. valkokir
    Joined: Oct 25, 2007
    Posts: 196

    valkokir
    Member
    from DeKalb, IL

    Here's the info I've uncovered about your braking system:

    Assuming a '68 Ford F100, have to assume but most 9" rears should be the same with 10" drums
    Rear wheel cylinders are probably 7/8" diameter
    Original master was 1" diameter

    '61 buick would have:
    1-1/8" diameter wheel cylinders
    Original master was 1" diameter

    We don't know what bore master you are running, I'm guessing 1" since that's what a mustang is and you say "mid 60's ford car"
    Based on these assumptions everything SHOULD work, of course if you have huge wheels or bigs and littles then it may very well not.

    Port size makes no difference, line size makes no difference.
    I'm guessing its as simple as not having the shoes adjusted close enough to the drum. I'd initially adjust the shoes out so there is slight friction on the drum before you touch the pedal. Not having the shoes adjusted out will make it seem like the master isn't moving enough volume which is basically what you are describing when you say pumping up the brakes allows them to work some. That's the residual valves helping you out by keeping the fluid from running back when the pedal returns.
     
  16. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    I don't honestly know the ID of the master cylinder. Just by looking, I'd say that 1" seems right. It is for a mid-60's galaxie, fairlane, etc. with drums front and rear.

    I figured it might be the shoes out of adjustment when I first drove the car, so I put it on stands and adjusted each wheel so the shoes drug to the point that the tire would not quite make a full rotation when it was spun. I did that with all four wheels. I haven't checked adjustment again since I've driven it (approximately 350 miles) so I suppose I should recheck them. The front drums and shoes came off the donor car and the shoes looked basically new. The rear drums and shoes are as they came and look very good with lots of pad left.

    So if I'm understanding everyone, it really doesn't matter which reservoir you have the front and rear brakes hooked to.....right? I'm looking at it all wrong when I assumed that the piston would apply pressure more to the first reservoir than the second....right?
     
  17. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    Oh, and the tires front and rear are bias ply 7.50X16 Firestone WWW's.
     
  18. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    I have new residual valves that are 10 psi in-line front and rear. They are clear visually and seem to be working properly.

    How can I tell if I'm bottoming out the MC? It doesn't seem to be the case, because when I press firmly on the pedal it gets harder, but if I really stand on it I can get more movement. It definitely feels like it gets firm well before it stops.
     
  19. 39 All Ford
    Joined: Sep 15, 2008
    Posts: 1,531

    39 All Ford
    Member
    from Benton AR

    "modern" drum brakes are "self energizing", meaning that the shoes kind of "roll" foreword to assist with pedal effort. If the brakes are installed on the wrong side of the car or if the shoes are on backward, they will NOT self energize and the pedal effort will be excessive.

    I would say that a M/C with a 1" bore would be right for power brakes, and maybe a 7/8 bore for manual brakes would be about right.

    I am using a 1" bore M/C on my 55 Lincoln (has 12" drums) with power brakes works very well. On first install, the power unit was not working, the pedal was a pretty damn hard without power.

    In my way of doing things, I want about 6" or 7" of total pedal travel and I want to have about 1 1/2" of pedal travel to remain before the pedal contacts the floor, (when pushing the pedal AS HARD AS I CAN).

    To me, this is an indication as to where I am with relation to "pedal ratio"... If I am short of this goal, (say 2 1/2" from floor) I INCREASE pedal ratio, If I get too close to the floor I REDUCE pedal ratio.

    I think you will find your problem with improper installation of the drum brakes and/or pedal ratio.

    (As an example, the TreadleVac M/C I removed from the Lincoln had about a 3/4" bore with about a 3" Stroke, the 1" Chevy master cylinder has a 1" bore with perhaps a 1 1/2" stroke. This change caused me to INCREASE the pedal ratio to accommodate the shorter stroke. I did this by effectively raising the pivot point for the m/c pushrod on the pedal arm.

    Before I raised the pivot point, the pedal was way, way, too hard to effectively stop the car... I DID NOT have enough leverage. )
     
    Last edited: Jun 16, 2009
  20. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    39 All Ford,
    I just measured the pedal at rest and then again at full depressed and the travel is around 4". The pedal basically stops about 3.5" from the floor. I have 3 holes in my lever arm off my brake pedal assembly. Currently, the mc pushrod is on the middle hole. If I'm reading you right, I need to move it to the outermost hole to increase my travel and move the "stop" distance closer to the floor. Is that correct?

    I can take apart the front drums, but I'm pretty sure I put the together like I found them. Are there any obvious things that I should look for to let me know I did it backwards?
     
  21. Harry Bergeron
    Joined: Feb 10, 2009
    Posts: 345

    Harry Bergeron
    Member
    from SoCal

    Drive in reverse, slam the brakes on.
    If the fronts lock, your problem is the shoes on backwards.
    If there's no change, that might still be your problem!
     
  22. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,222

    Da Tinman
    Member

    move it to the one closest to the pivot, that increases the ratio
     
  23. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    I think you would need to go the other way to accomplish that. Another thing. Make sure the pushrod isn't binding up in the hole in the back of the master cylinder while your under there.
     
  24. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    Ok, I'll move the pivot point to the hole closer to the axis. I checked the pushrod ball and socket when I put it together and it seemed fine. How can I check to see if they are binding now that there is fluid in the system?
     
  25. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,485

    landseaandair
    Member
    from phoenix

    If you can see inside the bore, push it as far as you can and check if it still has a gap remaining or maybe you could cut a straw lengthwise and use it as a feeler gauge?
     
  26. whenever I have a customer with possible brake pressure issues I suggest the following-

    first, your master cylinder should have residuals built in. Youi can check by removing the brake lines and LIGHTLY sticking an unfolded paperclip in the ports. DO NOT PUSH!!! You can puncture the diaphragm in the residual. If the paperclip goes a short ways and stops, there is a residual. If it goes in an inch or so, there isn't.

    Second- Aftermarket inline residuals are known to fail, and can cause pressure issues. The system may or may not bleed properly, but it won't get good pressure past the bad residual.
    SO-Jack up one end of the car, pump up the brakes and hold them. Try to spin a wheel by hand. It shouldn't take much pedal to hold the wheel solid. If the wheel spins- you likely have a pressure issue.
    Next, pump it up and hold it. Crack the bleeder WAY open- If the fluid SHOOTS out, Your issue is inside the drum- If the fluid dribbles, keep moving backward in the system cracking joints until you find the restriction.
     
  27. Billet
    Joined: Oct 13, 2008
    Posts: 275

    Billet
    Member

    adavis, The engineering of hydraulic brake systems can be some difficult shit, adding failure of individual components and the problem will make your hair turn gray. Check out this page concerning drum brake issues: http://www.flatheadv8.org/f1brakes1.htm

    The good news is that the solution will be something basic. The best baseball players still go to spring training and brush up on the basics. Here is a pdf that covers the basics of hydraulic theory: http://www.peterverdonedesigns.com/files/hydraulic system theory.pdf
    It would seem reasonable that the brake components you are using should stop you Model T on a dime and they just might "if" the problem/ defective component (s) can be repaired.
    It would be helpful if you have someone to help you troubleshoot the problem-
    I have had my share of shit brakes, I have never see your setup or used the components on your car, I'm a idiot and should never be taken seriously that said here ya go-
    Disconnect the master cylinder rod from the pedal to check that the rod length is correct- that there IS free play-or that the rod is allowing the mc piston to return. Adjust if needed or possible and measure the distance the rod travels when the pedal is depressed. This should help determine if the mc "bottoms" from the travel.
    Is there movement of fluid in the reservoir when the the brakes are applied and released? There might be a fountain of brake fluid created here- use a mirror and have the seal handy to shield the fluid from painted surfaces and your eyeballs!
    If everything seems good lift the front and check the resistance of the wheel when the brakes are applied. If they seem good remove the front drum and check the position of the shoes and pivot. Does one shoe have a longer lining- Is it in the correct position? Is the lining and drum dry? If the components are all new look at the shoes contact area. Does it appear to have contact to the drum. If not remove a shoe and place it in the drum does it rock excessively is it even close? It will not conform perfectly unless it has worn into the drum but there shouldn't be a gap in excess of the brake lining- wrong shoes or wrong position?
    These are some of the easy checks to make I hope it helps- Now I just wait for people to flame me for the tips- and they might be right-I probably shouldn't be able to post here!
    Good Luck
     
  28. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    I've definitely got several things to check and recheck. I do know (and didn't mention) that I have a fountain of brake fluid at each wheel when we bled the brakes. I am going to pull apart the front drums hopefully today and take some clear pictures....maybe someone can see if I've got them backwards. I took the complete buick drums and adapted them to my Ford spindles, but now that I think about it I honestly don't know if I have the left brake assembly on the left wheel and I had no idea that would matter. I appreciate all the advice and I'll keep posting until I figure it out. Thanks.
     
  29. adavis
    Joined: Oct 13, 2006
    Posts: 530

    adavis
    Member

    So I couldn't wait till this evening to tear one apart. I took some pictures and maybe that will help someone explain if the brakes are set up correctly.

    As you can see in the pictures, the larger shoe is leading or at the front of the drum. I believe this is correct but am I right? The front pad, however, is nowhere near making full contact with the drum. It only has wear on the upper 2-3 inches and a little bit on the outside edge. I spun the wheel before I took it off and it is dragging slightly, so how do I "seat" the shoe to fit the drum better? I had the drums turned before I installed them and they look good and have no wear.
    The back shoe has more uniform wear, but there is a section towards the lower middle backing plate area that is not making contact.

    I hope someone has done buick 12" brakes recently and can tell me if mine look right. Like I said, I didn't pay attention to which brake assembly came off of which wheel on the donor car, but I did set them up so the larger shoe was at the front or leading edge of the drum. Also, if anyone has advice on seating the shoes or a thread that already explains that I'd love to hear about that too.

    Thanks again everyone for your time and advice.....the HAMB is an amazing place with limitless knowledge.....
     

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  30. joeyjohn
    Joined: Aug 4, 2006
    Posts: 21

    joeyjohn
    Member
    from Minnesota

    I'm grateful that we have knowledgable folks on this site, I'm learning about brake systems and how they work before I get started on my "53 Ford. I've just muddled through brake jobs through the years and God must have smiled on me because I have always fixed the problem without killing myself or others.
     

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