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From: Dave on 7 Mar 2010 21:50 "Bill Putney" <bptn(a)kinez.net> wrote in message news:7vi6vgFct6U1(a)mid.individual.net... > jim beam wrote: >> On 03/07/2010 08:10 AM, Bill Putney wrote: >>> jim beam wrote: > >>>> i have done this. with the engine off, the vacuum remains until the >>>> pedal is released - thus if you stomp the pedal and keep it there, you >>>> don't need to keep replenishing the vacuum. and you will stop the car. >>>> with the engine running, there is no vacuum issue, and the brakes are >>>> still powerful enough to stop the car. on my honda anyway. >>> >>> I have real trouble believing that a large majority of people would, in >>> a sudden inadvertent acceleration situation, be content to press the >>> brakes one time and not try to pump them once or twice. >> >> why? if the car in front of you suddenly jams on their brakes, do you >> apply then release your pedal? i think your answer is "no" - unless >> you're skidding and know what cadence braking is. and if you know what >> cadence braking is, you should know that to stop a car with the engine on >> full throttle, you apply the brakes hard and quickly - you don't monkey >> about with multiple brake applications that can cause excess heating and >> fade. > > We aren't talking about what the savvy drive does and knows about. What > I've said still stands for the scenario we are talking about and for many > drivers. We weren't talking about what the best thing would be to do. > >>> After that, the >>> brakes will be almost totally ineffective because of loss of vacuum. >> >> no. fade maybe, but vacuum is always present if the engine is running... > > Not enough for any effectiveness of brakes. Do you even know what happens > to plenum vacuum at light, moderate, and heavy throttle? If you knew the > numbers, then you wouldn't be saying that an engine running (with throttle > open) will have enough vacuum to run the brakes - because it simply isn't > true. Anyone who has used a vacuum gage to any extent knows that vacuum > plummets when the throttle is open. > >> even if it's not, you still have vacuum reserve for three applications. > > That part is arguably true. I'd say you're loosing effectiveness after 2, > but what's one more jab of the brakes between friends. The result will be > that the booster will absolutely *not* charge back to any usable level > under acceleration. Plenum vacuum is just too low. Again - you don't > seem to know that - if you want to argue that point, then give me some > numbers for vacuum for a common engine of your choice at idle, and in gear > under light, moderate, and heavy acceleration. If the numbers you come > back with are honest, you will prove what I'm saying. > >>>> with respect, i think you're confusing vacuum with fade... >>> >>> No - I'm not. While you could certainly induce fade with a certain >>> prolonged script of usage of the brakes, what I'm talking about is true >>> over what I would say would be the real world typical scenario (before >>> the fade issue becomes real - which - yes - it would over a longer >>> period, but not likely if the 2 or 3 stabs had already occurred in the >>> relatively short period that I would expect). It is a fact that the >>> vacuum cannot recharge with almost no vacuum in the intake - it doesn't >>> recharge by magic. I guarantee you that after a third stab of the brakes >>> on an engine vacuum-driven power brake car, the brakes will loose the >>> fight with the engine - fade has nothing to do with that over the first >>> few seconds that we would be talking about (during which the first 2 or >>> 3 stabs would occur real world). >> >> if that is your experience, then i think you must have a vacuum leak... > > That is simply not the case. > >> even with wide open throttle, there is sufficient vacuum in the manifold >> to create significant braking assist. > > That is profoundly incorrect - period. > >>> i've >>>> experienced that too, one particular time on a major hill in san >>>> francisco approaching a busy intersection. yes, it's scary stuff. but >>>> when i changed the pads on my civic from after-market to oem, all fade >>>> problems disappeared. even fully loaded, repeatedly decelerating from >>>> speed. [i learned my "honda oem is best" lesson that way.] > >>>>> I urge anyone who doesn't believe what I claim above to try it before >>>>> commenting. >>>> >>>> i have. my results and comments are as above. > >>> And both of us could design the script to create either end result we >>> wished. I submit that in the real world, most people would try pumping >>> the brakes in desperation if the sudden acceleration scenario actually >>> happened - the depleting stabs would occur before fade became a factor. > >> sorry dude, it's incredibly rare for a panicking driver to pump their >> brakes... > > That's your *theory*, or you have something to back that statement up? > Admittedly, my theory that some percentage of drivers would pump the > brakes is not provable as far as I know, but I do state it as conjecture, > not as fact as you are stating your argument. > >> that's why abs exists - abs does that for them, and only in the event of >> traction limit being exceeded.. > > You're not talking about the same situation. Trying to stop a vehicle > with runaway acceleration is not the same setup as emergency accident > avoidance as far as paniced driver psychology. (Yes - there are > similarities, but don't turn that similarity into being equal.) > > There is no point in arguing with him Bill. He is an idiot, no matter which nym he's posting under.
From: Dave on 7 Mar 2010 22:13 "jim beam" <me(a)privacy.net> wrote in message news:F4udnUySrZ3GZQ7WnZ2dnUVZ_vQAAAAA(a)speakeasy.net... > On 03/07/2010 09:52 AM, Bill Putney wrote: >> jim beam wrote: >>> On 03/07/2010 08:16 AM, Bill Putney wrote: >>>> dsi1 wrote: >>>> >>>>> I certainly believe you. You can get a feel for the amount of reserve >>>>> vacuum boost on your car by simply repeatedly pressing down on the >>>>> brakes without starting your engine. If your brakes are working >>>>> properly, you'll feel the pedal getting firmer until you'll only be >>>>> able to move the brake pedal a couple of inches of deflection. At that >>>>> point, you'll have used up all your vacuum reserve. I figure that you >>>>> should be able to get around 3 stabs at the brakes with mostly full >>>>> boost. This means you'll only get maybe two chances for full braking >>>>> after the initial attempt at braking. That's the breaks I guess. :-) >>>> >>>> My recollection is that boost is noticeably diminished after the second >>>> stab, greatly diminished by the third stab - engine overpowers brakes >>>> for most common vehicles. >>>> >>> >>> maybe if the engine is stopped and vacuum gone. but if the engine is >>> running, you still have vacuum... >> >> Then give me some vacuum numbers for idle, and in gear light, moderate, >> and heavy acceleration for a typical engine. If you can show that >> moderate to heavy acceleration vacuum levels are anywhere near idle >> vacuum levels, then I'll concede. > > dude, for the typical vacuum diaphragm, you only need the smallest vacuum > to significantly boost brake pressure. do the math. > You have never driven a vehicle with vacuum actuated wipers, have you?
From: fred on 7 Mar 2010 22:35 clare(a)snyder.on.ca wrote in news:35c8p51cs5k40rluhev8lg1ubjs4m7t7kv(a)4ax.com: > On Sun, 7 Mar 2010 11:10:20 -0800, "theref" <theref(a)seanet.com> wrote: > >> >> >>"Grumpy AuContraire" <GrumpyOne(a)GrumpyvilleNOT.com> wrote in message >>news:99adnZJAetdSdQ7WnZ2dnUVZ_qidnZ2d(a)giganews.com... >>> bjn wrote: >>>> On Sat, 06 Mar 2010 10:38:19 -0500, Bill Putney <bptn(a)kinez.net> >>>> I'm not sure about this but for sure... The causes you cite >>> certainly contributed in getting to where we're at! >>> >>> Oh, don't forget that little incident when a B-777's engines went to >>> idle about a minute before touch down at Heathrow about a year ago. >>> Aircraft was totaled but there were no major injuries. >>> >>> Cause has been assessed to software/computer glitch. >>> >>> JT >> >>I believe that was traced to icing in the fuel system. SOP now is to >>cycle fuel after prolonged low temp at altitude. > Icing on a JET????????? > Don't think so. Why don't you actually *see* if it is the case. I'll tell you right now it is absolutely. When you have an object that does over 400Mph in place where the temperature can easily be -100 F icing on the wings is virtually asured. Have you never seen people up on an airliner's wing spraying some kind of fluid? What do you think they're doing? It's called deicing. That's it. Time to permanently take some of these useless groups out. I trust other people who *do* use the follow-up header as it's supposed to will remove them too. Two bloody *relevant* groups FCS.
From: clare on 7 Mar 2010 22:52 On Sun, 07 Mar 2010 18:05:07 -0500, News <News(a)Groups.Name> wrote: >clare(a)snyder.on.ca wrote: >> On Sun, 7 Mar 2010 11:10:20 -0800, "theref" <theref(a)seanet.com> wrote: >> >>> >>> "Grumpy AuContraire" <GrumpyOne(a)GrumpyvilleNOT.com> wrote in message >>> news:99adnZJAetdSdQ7WnZ2dnUVZ_qidnZ2d(a)giganews.com... >>>> bjn wrote: >>>>> On Sat, 06 Mar 2010 10:38:19 -0500, Bill Putney <bptn(a)kinez.net> wrote: >>>>> >>>>>> jim beam wrote: >>>>>>> if you buy all this fear-mongering idiocy that electronic throttle is a >>>>>>> problem, and that brakes, transmissions and ignition kill switches can >>>>>>> all simultaneously fail causing a driver to lose control, it might be >>>>>>> worth auto manufacturers of all stripes to adopt a slightly different >>>>>>> implementation of electronic throttle [e.t.] - if not for mechanical >>>>>>> reasons, but to shut the idiots up... >>>>>> The lawyers, politicians, and news media can convince the public of the >>>>>> impossible (failure even a totally fail safe system) any time they >>>>>> decide to do it depending on political or monetary motivation. IOW - >>>>>> the people and companies who do a good job of designing are going to get >>>>>> punished anyway (unless they know how to play the game in a corrupt >>>>>> system). There are people in our society whose life goal is to make >>>>>> sure that that happens. >>>>> >>>>> The problem is that now lawyers, politicians and news media are driving >>>>> (no >>>>> pun intended) solution. The way I see them talking, cars will wind up >>>>> with >>>>> a fail-safe throttle that is more fail-safe than the controls of a jumbo >>>>> passenger jet. >>>>> >>>> >>>> I'm not sure about this but for sure... The causes you cite certainly >>>> contributed in getting to where we're at! >>>> >>>> Oh, don't forget that little incident when a B-777's engines went to idle >>>> about a minute before touch down at Heathrow about a year ago. Aircraft >>>> was totaled but there were no major injuries. >>>> >>>> Cause has been assessed to software/computer glitch. >>>> >>>> JT >>> I believe that was traced to icing in the fuel system. SOP now is to cycle >>> fuel after prolonged low temp at altitude. >> Icing on a JET????????? >> Don't think so. > > >Absolutely. Determined to be cause of BA 777 landing short at Heathrow. OK - I looked it up. Technically this was fuel jelling - common with diesel fuel in arctic conditions. In the case of the Rolls turbines, it was a design fault in the fuel pre-heater unit which resulted in a mandatory replacement with a redesigned heat exchanger. Different than the carb icing on a prop plane.
From: clare on 7 Mar 2010 22:58
On Sun, 07 Mar 2010 18:09:05 -0500, Bill Putney <bptn(a)kinez.net> wrote: >clare(a)snyder.on.ca wrote: > >> Sorry Jim - but you are wrong. >> A diesel engined vehicle with a mechanical vacuum pump would work as >> you envision - but under any substantial load there is not enough >> manifold vacuum produced to provide full braking assist. With both >> feet on the brake pedal a strong man MAY be able to provide enough >> brake line pressure to stop the car at half throttle. > >Kind of related: In the early 80's (of the last century), when cam >design rules were changing (I think to provide overlap, etc. for >emissions - not 100% sure if that was the exact reason, but I think so), >vacuum levels dropped on engines. Before other methods were figured out >to compensate for that (I'm guessing just building the boosters larger >and futzing with the design of the master cylinders and calipers so the >assist worked well on generally lower vacuum), GM had to install >electrically driven vacuum pumps in the fenders of some of their cars to >provide sufficient booster vacuum. > >I found out about that after I installed a "recreation" cam on a 1980 >Chev. Citation after its factory cam wore out. After installing the new >cam, the brakes had insufficient assist because the cam design dropped >the vacuum levels. I researched it and found out about the electric >vacuum pumps and went to a junk yard and grabbed one and installed it (I >think from a Pontiac J2000, J4000, or J6000 - something like that) - >anyway, it worked *great*. > >In my research at the time, people also told me that electric vacuum >pumps and/or extra vacuum reservoirs were often used on race cars for >the same reason (hi-perf. cams and low vacuum during acceleration). Correct - on the GM J and X series cars between 1982 and 1986 a backup vacuum pump was installed. At idle with the AC on there was inadequate vacuum to provide braking. |