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A Fresh Start on Toyota's Brakes

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  • A Fresh Start on Toyota's Brakes

    I'd like to start afresh talking about Toyota's brake pedal problems. Papers and other media have recently started giving out illustrations of how the new shims will fix the problem. These illustrations show some kind of tongue-in-groove assemblies that can fit too tightly together, and the shims will move them apart slightly.
    I can't figure out why these tongue-in-groove configurations are at all needed. Doesn't the pedal just provide a mechanical linkage to a master cylinder push rod? If so, what is wrong with a simple lever assembly?
    I'd appreciate it if someone could enlighten me as to why a brake pedal needs to have such involved parts that are much more prone to problems. I'd go to the local Toyota dealer and ask, but they are probably pretty busy right now.
    If ignorance is bliss, why aren't there more happy people?

  • #2
    Finally found an illustration like I've been seeing:

    If ignorance is bliss, why aren't there more happy people?

    Comment


    • #3
      Hmmm, and putting a spacer to limit the travel is supposed to loosen the Acme thread looking part at the top of the pedal pivot.

      Ummhhhmm, when pigs fly.
      It's only ink and paper

      Comment


      • #4
        ?

        Which do you mean?
        You state brakes in first post, but show accelerator pedal in second post.
        Advise please...
        Tom

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        • #5
          It looks as if the teeth have too tight a tolerance and stick when fully engauged. The shim looks like it is intended to prevent full tooth engaugement. Seems like a cheap fix. I would think a redesigned shoe/pedal assembly with more clearance would be a better solution.

          Comment


          • #6
            its hard to keep track when the same company manages to fail at both pedals, the only major function of the car they havent managed to screw up is the steering.. at least, this year.
            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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            • #7
              In addition to any mechanical fix, killing throttle when the brake pedal is pressed (like cruise control) would be a smart move, but.. that would mean changing code/chips on the computers, and a lot more expensive to retrofit in comparison to the above. A error could also be generated/logged if the throttle is "stuck"... Could have saved a couple of lives.

              Comment


              • #8
                Hmmm, it looks like to me when the pedal is fully depressed, it causes the shoe to pivot forward at the top and the teeth to lock togethor... possabley reguardless of 'moisture' (though im sure humidity causes the plastic to expand past some frivious tollerances that where made to insure this could not happen if the world stayed at exactly 20c and 50% RH), and the shim just prevents the shoe from pivoting forward as much.. Possabley still allowing the origional fault if the shim falls out of place, or the plastic deforms with time or flows. (Bet they just glue the shim in place or something)
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                • #9
                  Toyota may be blowing smoke about this problem. There are a few embedded software columnists who think the shim fix might be grasping at straws when the real error is in the software that controls the throttle. It is my understanding that these toyotas with the accelerator problem are drive-by-wire: the pedal is not a mechanical linkage to the engine at all but a sensor input into the ECU. Only time will tell whether the sudden accelerations go away with the shims. It will be a bad day if it turns out that the problem is actually software.

                  --Cameron

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                  • #10
                    Originally posted by Black_Moons
                    its hard to keep track when the same company manages to fail at both pedals, the only major function of the car they havent managed to screw up is the steering.. at least, this year.
                    -Um, no. The issue with the car has been a possible sticky throttle pedal, causing the car to accellerate out of control. As in the accellerator pedal doesn't snap back up as it should when released.

                    What we were talking about here, was the fact that, in one of the accidents, the driver, who was unused to the car, was apparently unable to shut the engine off (apparently due to the "push to start" button as opposed to a conventional ignition key) nor shift it into neutral (again, supposedly due to his unfamiliarity with the car's "sport" shifter gate, which probably had a mild interlock so you didn't snap the thing into neutral instead of just shifting) which in turn led to him burning the brakes out and subsequently crashing.

                    The "official" issue was the sticky acellerator. The issue we were arguing about was the brakes.

                    Doc.
                    Doc's Machine. (Probably not what you expect.)

                    Comment


                    • #11
                      That's the most uninformative technical illustration I've seen in a long time.

                      My questions are:

                      Is the pedal shown in the idle or WOT position?

                      What holds the shoe in place?

                      How exactly does moving things closer together decrease the friction?

                      What is the reinforcement bar reinforcing?


                      In the side view, it appears the shim will keep the pedal from going down all the way. That should ease the load on the brakes when the pedal sticks.
                      Any products mentioned in my posts have been endorsed by their manufacturer.

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                      • #12
                        Originally posted by winchman
                        That's the most uninformative technical illustration I've seen in a long time.

                        My questions are:

                        Is the pedal shown in the idle or WOT position?

                        What holds the shoe in place?

                        How exactly does moving things closer together decrease the friction?

                        What is the reinforcement bar reinforcing?
                        You must realize that this is not a true engineering diagram. I suspect this "technical illustration" wasn't even produced by Toyota. Media companies (they ain't "news" organizations anymore) are notorious for not having a clue about hard sciences or engineering, and often their simplified illustrations (for the likewise undereducated public) are very lacking in both detail and accuracy.

                        So of course they are not going to show how the shoe is held in place, nor how the "reinforcement bar" (i.e., I'm sure a more accurate name for this is "shim") will be held in place. But it appears to me that the shim is causing the shoe to pivot (rotate counterclockwise) so that as the bottom is moved by the shim toward the pedal, the top of the shoe moves away from the pedal friction teeth.

                        In the side view illustration, the pedal is signaling WOT. Apparently that is also when you have full engagement of the teeth between the pedal assembly and the shoe. Realize that since there is no mechanical linkage between the pedal and a throttle plate, then there must be a way of producing friction for driver feedback (i.e., the feel in the foot). That is the purpose of the "shoe". Imagine how disconcerting it would be to try to operate an accelerator pedal that has little friction and is simply a spring loaded lever.

                        Comment


                        • #13
                          Originally posted by lakeside53
                          In addition to any mechanical fix, killing throttle when the brake pedal is pressed (like cruise control) would be a smart move, but.. that would mean changing code/chips on the computers, and a lot more expensive to retrofit in comparison to the above. A error could also be generated/logged if the throttle is "stuck"... Could have saved a couple of lives.
                          How many lives have been lost due to this problem? As far as i know, the only fatalities that POSSIBLY involved this pedal assembly were from the wreck in San Diego involving the Highway Patrolman. And we still don't know the exact cause of that mishap, with an improper floormat being the most probable causal factor at this time.

                          Comment


                          • #14
                            Looking at the bigger picture, why is Toyota being singled out for recall, halted sales, and factory shutdowns? Consider that CTS, the company "that supplies some Toyota models with the gas pedal in question, also supplies the same gas pedal to Honda, Ford, GM and Chrysler." And that other cars -- including cars made by GM and Chrysler -- have also had similar sudden unintended acceleration complaints filed with the National Highway Traffic Safety Administration, yet have not been subject to government-mandated recall.

                            Perhaps the Obama administration and the UAW have it in for Toyota, which is both very successful and non-union. Since Obama is now a co-owner of both GM and Chrysler, what better way to cut out the competition than to use the unlimited power of the federal government to attack your chief business rival? Yet another reason why socialism fails.

                            Read the article here.

                            Comment


                            • #15
                              Originally posted by lakeside53
                              In addition to any mechanical fix, killing throttle when the brake pedal is pressed (like cruise control) would be a smart move, but.. that would mean changing code/chips on the computers, and a lot more expensive to retrofit in comparison to the above. A error could also be generated/logged if the throttle is "stuck"... Could have saved a couple of lives.
                              Cutting the throttle if the brakes are applied has been tried.

                              Customer acceptance was pretty much zero and it didn't go into production.

                              Many drivers of automatics rest their left foot quite heavily on the pedal. One of the old racing brake compounds was actually developed by Ford for just this reason.
                              Paul Compton
                              www.morini-mania.co.uk
                              http://www.youtube.com/user/EVguru

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