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Technical brakes again, master cyl selection

Discussion in 'The Hokey Ass Message Board' started by theHIGHLANDER, May 22, 2017.

  1. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,245

    theHIGHLANDER
    ALLIANCE MEMBER

    I'm into the on going struggle of this build takeover and can't seem to get an acceptable pedal feel. Everything is new, no old rusty parts, mullered up rubber lines, Wilwood 4 piston Dynalites on all 4. It's equipped with a 1" bore master. The pedal was cut to get it closer to the floor (yeah, I know) but any higher would introduce a drivability issue. I have a total available master cylinder stroke of 1/2", the total stroke of the cylinder is just over 1". Still, since when does any brake system worth it's fluid need more than about a 3rd of available travel or cylinder stroke to lock up the brakes (with all new parts, bleeding done right, etc)? If I calculated the displacement of the calipers right from their tech site we have about 16.48 cuin. Several sites place this system right in the middle of whether or not a 1 1/8" master is required. I can bottom the pedal easily right now, I can "ghetto pump" some additional pressure, there's not a drop of air in the system, the master is perfect, bench bled to perfection, fluid is full, all braided stainless/teflon flex lines, all stainless hard lines. This was new chassis engineered and assembled by Lobeck's back a few years ago so I had no reason to 2nd guess this gig. I'm about as fed up with this shit as I can be but I figured before I completely display a white flag over this I'd seek some help here. It is, afterall, a 33 Ford hot rod so there's that. Maybe not 100% in favor of our stuff but the parts being standard rod fare I see no foul in asking. It's under the floor, there's 2 2lb residual valves in the right place flowing the right way, there's also an adjustable proportioning valve at about 1/2 the total setting. Can't even play with that because I can't get "proper" pedal feel yet. Thanks in advance for the help as I don't want to simply throw parts at a problem especially since everything's brand new. And yeah, we service, modify and restore daily so we're well versed but this one's a little bitch hell bent on tormenting us to the end.
     
    patrick2965 and chryslerfan55 like this.
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,935

    squirrel
    Member

    How much travel does the pedal have (till it bottoms)? you said it's cut...is it cut in half? or only lost a little bit? or what?

    Put smaller calipers on the back, you only need half as much action back there....just a thought. and use a larger bore MC. and give it a little more pedal travel. That should fix it.
     
    patrick2965 likes this.
  3. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,245

    theHIGHLANDER
    ALLIANCE MEMBER

    Just about 3" from "up" to the floor. It equates to a little over 1/2" in the master.
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 55,935

    squirrel
    Member

    normal pedal travel would be over 6"?
     

  5. What if the pedal ratio was decreased? Longer at the M/C end?
    I'm catching 6:1 or close. And with a lesser ratio that falls in range, pedal feel is stiffer as the master cylinder travels farther. 4:1 at where I would want to be only if I had power assist, but still on low end.
    Shame on me. The proper description is to increase, like a higher gear ratio.
     
    Last edited: May 22, 2017
  6. i sure would want to be able to have full travel of the master cylinder if there was a problem.
    redesign that pedal set up.
     
  7. That's it right there.
    Purely for safety reasons the cylinder should bottom before the pedal hits the floor.

    I've seen it a hundred times. The stuff doesn't fit, travel is limited, drivability and foot room is a issue sooooo cut the stuff and make it fit, ALL fit. A few months later the fluid get added and then the problem shows up. At that point there's a big redesign
     
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  8. squirrel
    Joined: Sep 23, 2004
    Posts: 55,935

    squirrel
    Member

    Changing the pedal ratio does the same thing as changing bore size...sort of...

    There's no magic solution.
     
  9. Happydaze
    Joined: Aug 21, 2009
    Posts: 1,903

    Happydaze
    ALLIANCE MEMBER

    3" of available pedal travel doesn't sound at all right. What's so unusual about this '33 Ford that the pedal has to be so restricted?

    Chris
     
  10. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,245

    theHIGHLANDER
    ALLIANCE MEMBER

    It's a Speed33 body. For the record my brethren, I didn't set this shit up. It was a takeover and finish gig, now several errors have shown up. Some things had never occured to me to "engineer" or check. It ran and drove and he was fine with it. Well, that is until we actually put miles on it. The travel may be more than 3" as I visualize things, but it's still limited to about 1/2 of the available cylinder travel. I'm about ready to kick it to the curb, and sure a shit someone will think this was all us when that happens.
     
  11. I caught the part where you took it over. Around here, plenty of things come in wrong, But They don't leave that way.

    Your particular issue needs study to determine the problem that needs correction vs chasing and treatment of the symptoms.

    i guess it all depends on what the limiting factor is. Then work from there.

    If that limiting factor is the 3" of pedal travel- the pedal ratio should be 3:1 and not 3:0.5 with a cut pedal. That means it needs a booster. The booster doesn't need to go back to back on the pedal mount either. You can move it back.

    Sure if you move it back the lines will need to be redone, maybe brackets deleted or added and hopefully the frame isnt powder coated already. Then exhaust pipes and everything else might be in the way.

    My Dad always drilled the priority list,
    Make it stop
    Make it Go
    Make It pretty
    And always in that order.
    Apparently someone jumped the order and now there's a mission to correct it. It's yours to accept or decline at this point. You can't assume responsibility for someone else's mistakes in engineering but you can correct them.
     
    Johnboy34 and tb33anda3rd like this.
  12. from what i believe from your past posts, if we were discussing a paint process you wouldn't settle for anything less than the best. done right from the steel to the miles deep perfect finish. bad paint doesn't kill. don't give up. it sounds like another three days of paying work. it's spring so you probably are swamped with work and an extended project throws off the schedule but it' BRAKES man.
     
    31Vicky with a hemi likes this.
  13. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    I've had similar problems with the Wilwood black MC. Wilwood designed the system, dynalites on all 4 corners and 1" bore MC. I had the same problem and I assumed I made an error in the pedal ratio so I bought their 15/16ths MC and still couldn't get pressure. I replaced the MC with a 1" Strange MC and problem solved. I think the compensation port or something is open too long so too much fluid goes back into the bowl and not out to the pads. It takes more volume than you'd think to operate a disc brake, its a lot of square inches, thats why the front bowl is bigger on a disc/drum MC to accomodate the volume. You have a 1sq bore MC sending fluid to 16sq inches of pads, think about it.
     
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 55,935

    squirrel
    Member

    the reservoir volume is larger on the front brakes of a disc/drum system, to account for the fluid that gets stored in the calipers as the pads wear.
     
    stimpy likes this.
  15. BJR
    Joined: Mar 11, 2005
    Posts: 9,814

    BJR
    Member

    From what I have read you MUST have full travel on the master cylinder pistons for the dual braking safety feature to work if a caliper or hose breaks. Start with the pedal and master linkage to get 6 to 1 ratio with full travel. If thats not right anything else you do will just be a work around with hidden problems.
     
  16. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,245

    theHIGHLANDER
    ALLIANCE MEMBER

    It's a 1" Vette style master under the floor, the calipers mentioned, it also has a 7" booster (dual diaphragm booster maybe). What "they" did to get pedal was partially engage the master. They simply lengthened the push rod. Yeah, exactly, drive it about a mile or so and it starts to lock up because there's "somebody riding the brake" all the time. I ignored the whole gig today to catch up on other work. As things are I can only reduce pedal ratio to get more travel at the master. By that I mean get more per inch at the pedal. And yes, it's an all done car with a powder coated chassis, finished paint, full bright white leather interior. Moving the floor ain't happening, changing the whole get up, maybe(?), decrease ratio since it's boosted anyways, and yeah, someone in their infinite wisdom decided this little 302 Ford motor had to have equal length long tube step headers. That shit in itself created nightmares that I'm not sure are over yet. I do appreciate the support and ideas. Maybe some input sparks an idea I may be simply to close to. Thank you....
     
  17. rbohm
    Joined: Dec 16, 2006
    Posts: 36

    rbohm
    Member
    from tucson,az

  18. Easy peazy man.

    You'll have to repaint the pedal.

    Make the bottom pivot longer. Done
    image.jpeg

    You have a booster already so you want a 4:1 ratio. 3:1 ain't too bad and worst case the piston bores get swapped to fine tune it if the pedal effort is too hard. Truth be told I've gotten 2.5:1 pedal ratio to stop incredibly well by taking every mechanical advantage I could get. 3" of travel was all I could get.

    #1 must have is full stroke on the master cylinder. After that you just make it work.

    It's kinda finicky drawing it up and getting the arc of the rod hole centered over the swing. A little finess here and you can kick it to the curb with brakes that work.
     
    Last edited: May 23, 2017
  19. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,245

    theHIGHLANDER
    ALLIANCE MEMBER

    Thanks, I appreciate the input. I'm sort of there with essentially reducing ratio. Still wears me out that 1/2 the available travel in the cylinder doesn't net a solid feel. I can easily push harder and feel like I could push "through" the system, yet by all calculations (minus the pedal inside) it should be good brakes. I hate following amateur fuckin idiots. This came to light the 1st time because some genius mounted the horn with 3/16 of the brake pedal rod. It had good pedal, when it was bottomed on the fuckin horn! "Step away from the hot rod!" shoulda been spoken to these mopes a long time back. Oh well, if was easy...
     
  20. What you're describing sounds like what I did, including the Chinese Corvette master cylinder.
    I misfired on the booster to master pushrod length to make the brakes drag.
    Then after fighting brake caliper piston leaks, I changed over to GM calipers without a park mechanism. The damn master cylinder started bypassing. Thankfully I had bought a spare at the same time.
    The spare master cylinder I kept in my house as a spare wouldn't even allow the piston to travel full stroke!!!:mad:
    So I said SCREW IT! I put a master cylinder for a '78 Chevy 1/2 ton with power brakes and finally have damn brakes.
     
  21. That's a good thing right? When stuff wears you out? :D
     
    tb33anda3rd likes this.
  22. In my situation my pedal pivot had been mounted about 1" too high and I have been going through the same thing with my pedal ratios.
    In my case extending the lower arm on the brake pedal would make the alignment of the master cylinder difficult.
    I cut the toe boards and built a box, 3/4" at the top and tapering to the floor boards to cover the pedals and now have a full stroke on the brake and clutch. I will fill in the sides with filler so the toe board is again flat. IMG_0862.JPG
     
    Last edited: May 25, 2017

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