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Weird Brake Problem

Discussion in 'The Hokey Ass Message Board' started by Hellfish, Sep 18, 2010.


  1. So what you are suggesting is this guy redo his brake system based on an assumption that the proportioning system may not be correct.

    I also noticed you ignored my plea to explain how presumed faulty brake proportioning would cause the pedal to go to the floor. Or how wiring in the brake bias waring light switch would make the system better. Fine, I'll let you slide on that because I seriously doubt you're going to be able to.

    Look, for all your experience with braking systems your suggestions aren't really helping here. I don't want to send this guy off on some wild goose chase in brake proportioning before we solve the first problem. Let's get some brake pedal, let him drive it and then determine if adjustable valves, metering blocks, hold off valves are necessary.

    Would you mind telling that to the guys at Raybestos? They didn't get the memo.

    http://www.raybestos.com/wps/wcm/co...b766d05ee771/BPI-00-06rev6-06.pdf?MOD=AJPERES

     
  2. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    OK, I measured the bolts on the calipers and they're about 5.5". I clamped the hoses (although I'm not sure I clamped them tight enough. I pressed on the pedal and it went down about the same amount, but felt harder. When I let go, the pedal popped right up, but it honestly felt like the spring was doing all the return work. Not sure if that's what MPB meant. Sounds like it may be a QTU, but again, my situation sounds different from Fitzee's.

    BTW, the pedal gets firm 2-3" from the floor, not 1" as I originally thought. I realized that I had the rear drums off on my last test (long story). It looked like the cylinders had tried to move out the shoes. I reset them, re-installed the drums, and adjusted out the shoes so there's quite a bit of drag. This may be why my pedal is a little higher. I cracked open a front speed bleeder and the pedal went all the way to the floor effortlessly as before, so basically same results. I wish I could take this for a drive to check brake/pedal feel and stopping power but I won't be able to until this weekend (again, long story)

    I measured the stroke. The pedal goes through the floor and has a metal stopper on it to prevent it from going too high. I know that the stock pedal ratio in an Econoline is 6:1. By myself, under the van, I really couldn't depress the pedal enough or get an accurate reading, so I cracked open one of the front speed bleeders allowing the pedal to go the full distance.

    From full upright (stopper hitting the floor from below), to all the way down (pedal pad on the floor above), the distance is about 5.5". The push rod moved about 3/4" although all of this was hard to measure by myself under the van. That sounds about like stock, but maybe not.

    I'm going to go out there now and disconnect the push rod from the pedal and see how far I can push it. Should be fun in the dark. :D I'll try to measure freeplay, too.
     
  3. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    Most MC's have a stroke travel ranging from 1&1/4 to 1&1/2 inches,so your pushrod needs to move at least 1&1/4 with full pedal travel.I realise that doing some of this checking buy your lonesome is aPITA as I too usually work by myself.
     
  4. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,226

    Da Tinman
    Member

    I know this may be a dumb question,, but is the m/c plumbed correctly?

    Had exactly this same issue on the wifes falcon using the same m/c that your using.

    flipped the lines front to back and it worked perfectly. yes I felt like a complete dipshit afterwards.
     
  5. lewislynn
    Joined: Apr 29, 2006
    Posts: 1,444

    lewislynn
    Member

    There's no reason for you to be snarkey. If you want to be the soul source of information, get his phone #
    I checked the Vise Grip website and didn't find anywhere where they claimed to be "a special hose clamp" for brake hoses...THAT is what Raybestos recommended NOT frigg'n Vise Grips with tubing. You don't have to be an engineer to know you don't pinch or kink high pressure hoses...especially ones your life depends on.

    If you'd actually go back and read the Raybestos link you posted (AKA practice what you preach), you'd see there are only a few reasons for his problems one of which was what I suggested, sorry you can't understand that it can be a m/c. Also if fluid is bypassing/leaking by the piston where would it go that I couldn't see fluid movement Einstein?
     
  6. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,226

    Da Tinman
    Member

  7. Ahem, I think you are reading much more in my posts than I put. Where did I claim Vise Grip ever made special hose clamping pliers? I didn't, I supplied a suggestion on how to do it with tools and parts he may have already.

    I have seen similar clamps like Da Tinman posted, these are the ones I am more familiar with.

    [​IMG]


    Fact of the matter is rubber brake hoses are much more robust than you guys are giving them credit for. Companies like Raybestos and MightyVac are suggesting this as a method of diagnosis, I have read the same in a few service manual and text books from years gone by. I have seen this in practice in auto shops for decades without ill effect. It is wise to not get aggressive in any instance, but to protest as you have is unfounded.



    LOL, now who is being snarky. :D

    It could very well be a master cylinder. Without information, we don't know for sure, do we. All I'm trying to do is diagnose the problem based on my experience with very similar systems. I want Hellfish, and in turn everyone else who reads this to learn how to diagnose the problem without having to spend needlessly buying new parts he doesn't need.

    But to answer your question about fluid movement in the master cylinder. If you move a piston through the master cylinder bore and the seal on the piston is damaged or not sealing any more the fluid just goes around the seal from the front of the piston to the back. If its a hard concept for you to understand, take a pitcher out of your kitchen cabinet. Fill it with water to within an inch or two from the top with your fist at the bottom of the pitcher. Slowly pull your hand out of the pitcher and be amazed that the enter volume of water doesn't come out with your fist.

    Is that enough snark for you :cool:
     
  8. BJR
    Joined: Mar 11, 2005
    Posts: 6,235

    BJR
    Member

    Here is your problem, you are not getting enough movement of the master cylinder piston, if you were correct in measuring only 3/4" piston travel with the pedal to the floor. Something is wrong with your pedal ratio if all the movement you get at the MC piston is 3/4".
     
  9. Got a bit more time now to dissect this.

    Sounds as if you didn't pinch hard enough, but there is some information there, you did have more resistance pushing the pedal and the clamps on the lines are acting like residual valves. It probably was the spring returning the pedal without the fluid transfer.

    Going to be hard to get a pedal if there isn't any thing for the brakes to work against. :)

    Just so we are on the same page now. I the last quote box here you stated the pedal gets firm 2-3" from the floor and in this last quote box you state you have about 5.5" of available pedal travel. This means you are pushing the pedal down 2-3", that's not abnormal.

    Unless I'm misunderstanding what you are putting up here.

    If the pedal above the floor can be depressed 5.5" inches and you know for a fact the pedal ratio is 6:1 then you can deduce that you have just under 15/16" of pushrod travel. This may very well be your issue.
     
  10. ECIGUY
    Joined: Feb 24, 2009
    Posts: 111

    ECIGUY
    Member

    You guys are making this way more complicated than it needs to be. Go back to the basics and start over. Look at the pedal ratio and m/c bore size.
     
  11. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    yeah, stupid... but OTOH, nothing really changed when I put the drums back on


    Yes, BUT *sigh* the combo valve may NOT be. I swear I checked twice before plumbing the lines, but I think I goofed something when I pulled it apart and had to replumb one. I'm going to tackle this one tonight and hopefully have an answer by morning.

    Grrr.
     
  12. I agree with ECI Guy, KISS.

    If the combo valve is installed backward meaning the end of the master cylinder is plumbed to the rear line of the combination valve, where the metering valve is and then plumbed to the front brakes I could see an issue with the braking bias and not stopping the van correctly. Still shouldn't cause a low pedal.

    Not being able to cycle the master cylinder piston the full travel can give you fits trying to bleed it out. See if you can borrow or rent a power bleeder, make sure the system is clear. Beyond that the pedal to pushrod stroke should be dealt with for safety reasons.

    The ratio and bore seem acceptable, it's the stroke length that's a bit off.
     
  13. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    It's not plumbed that backwards, but I may have gotten an inlet/outlet crossed for the fronts. The holes are next to each other. I'll find out tonight.

    BTW, I also checked the freeplay. I have about 1/8" of freeplay.
     
  14. Not knowing what valve you have, as long as all the front brake lines are on the same end of the valve it shouldn't matter much.

    Take another look at the drawing of the valve I posted, there is nothing in there that would determine which is in or out of the block.

    [​IMG]
     
  15. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    More like this

    [​IMG]
     
  16. With the metering valve in the system like this one it is more important which port you use for the inlet.

    Surprising enough, you find that same style valve with one or two ports to the front brakes. Classic Performance Products sell theirs with a plug in one of the two front ports so you can have a single line to the front brakes and T the left and right at a more convenient place.

    Just so happens I am running brake lines on a 1938 Cadillac and we are using 1996 Fleetwood calipers, rear axle and the master cylinder and booster combo. All for the low drag stuff, and the combination valve on it only has one port to the front wheels. They split the line to the front and rear at the ABS valves. Crazy stuff.
     
  17. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    The MPB instrcutions for the combo valve says you can block off one front outlet and run a single line to a T fitting, which is what I did.

    I got the lines switched. No real change, except when bleeding the rears the pedal goes all the way the floor now, like the fronts. At least I know it's right now.

    I got into a better position and tried to measure the pushrod movement again. With the system pressurized and me under the van, I could only move it about 1/2". I didn't measure the pedal. I opened a bleeder and measured again. With the full throw of the pedal (full up to all the way to the floor) the push rod goes in 1". I disconnected it from the pedal and pushed it in as far as it would go by hand. Still 1". Which says to me that it's the correct 6:1 ratio.

    Something tells me that everything may be OK now, but I can't really get out and test it until my rear seasl come in. They were supposed to be in today, but only 1 showed up (or NAPA last the other one).
     
  18. Even if the pedal pad travels 3", are you getting a firm pedal now?
     
  19. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    Yeah, pretty firm. Not rock hard, there's some givem but that's normal, and the pedal is higher than it was. I may have had some air in the system that I got out during all the testing. As soon as I can get it on the road I'll know if there have been any peformance improvements. It barely stopped before.
     
  20. Hellfish
    Joined: Jun 19, 2002
    Posts: 6,426

    Hellfish
    Member

    So, my rear seal finally came in... after waiting a week for a Ford 9 inch seal.

    I drove the van around the block a few times and the braking is a LOT better. I didn't really get to slam on the brakes too hard, but it definitely stops well. I may change up to a 1" more MC this winter, but the 15/16 bore is doing fine for now. If I make the switch, I'll drag this thread back to the top and report on the comparison.

    I wish I could tell you what I did that solved the problem, but I did a lot before I was able to drive it again. My guess is it was a combination of some air left in the system, but mainly the incorrect plumbing of the combo valve.

    Thanks for EVERYONE's opinions. I learned a lot.
     

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