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#41
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On Tue, 1 Feb 2005, N8N wrote:
> Discs *do* require more line pressure for a given brake torque than > self-energizing drums, assuming similar diameters and normal piston > sizes. Simple, indisputable fact. Definitely simple and indisputable, but why are you being so obtuse as to pretend this is even close to half of the story? "Needs more line pressure" does NOT necessarily equate to "Needs a power booster". There are *many* ways of varying the mechanical advantage of the driver's foot over the disc caliper pistons. DS |
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#42
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In article . com>, N8N wrote:
>> Nate, there's absolutely NO engineering basis for that statement! That >> was my whole objection in the first place. The fact that there have been >> several (incorrect) assertions made in this thread about "why" disk >> brakes "need" power assist does not make it true. Disk brakes do not >> "need" power assist any more than drum brakes, whether or not the drum >> brakes are of the self-energizing variety. > So you're saying that all those years of engineering school and > experience actually working as an engineer with automotive braking > systems were for naught. The fact that you don't like my explanation > doesn't mean it's not true. Discs *do* require more line pressure for > a given brake torque than self-energizing drums, assuming similar > diameters and normal piston sizes. Simple, indisputable fact. > > nate > > (damn, I really hate it when I have to play the "credentials" card, but > willfully ignorant people just **** me the f**k off!) A simple machine design textbook proves you're right nate. The self energizing feature is the advantage of drums. |
#43
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N8N wrote:
> Steve wrote: > >>Nate Nagel wrote: >> >>>Steve wrote: >> >>>>And the pedal effort in a 4400-lb 1969 vehicle with manual disk > > brakes > >>>>is NOT significantly higher than the pedal effort in a Honda > > Accord of > >>>>today. And disk vs. drum makes no difference at all. I just don't > > see > >>>>whay the staement that power boost "is a necessity with disk > > brakes" > >>>>keeps popping into discussions. >>>> >>> >>>*sigh* >>> >>>I'm not typing my explanation of it again. It is far more likely > > to be > >>>necessary with discs than with drums. search this thread for it. >>> >>>nate >>> >> >>Nate, there's absolutely NO engineering basis for that statement! > > That > >>was my whole objection in the first place. The fact that there have > > been > >>several (incorrect) assertions made in this thread about "why" disk >>brakes "need" power assist does not make it true. Disk brakes do not >>"need" power assist any more than drum brakes, whether or not the > > drum > >>brakes are of the self-energizing variety. > > > So you're saying that all those years of engineering school and > experience actually working as an engineer with automotive braking > systems were for naught. The fact that you don't like my explanation > doesn't mean it's not true. Discs *do* require more line pressure for > a given brake torque than self-energizing drums, assuming similar > diameters and normal piston sizes. Simple, indisputable fact. True, but requiring more line pressure isn't the same thing as requiring power assist. This is only true if the additional line pressure required increases the pedal effort so much that a typical human hasn't enough leg power to make them perform adequately. I don't think this is the case across the board with disk brakes. I think that is the other person's point. Matt |
#44
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Daniel J. Stern wrote:
> On Tue, 1 Feb 2005, N8N wrote: > > >>Discs *do* require more line pressure for a given brake torque than >>self-energizing drums, assuming similar diameters and normal piston >>sizes. Simple, indisputable fact. > > > Definitely simple and indisputable, but why are you being so obtuse as to > pretend this is even close to half of the story? "Needs more line > pressure" does NOT necessarily equate to "Needs a power booster". > > There are *many* ways of varying the mechanical advantage of the driver's > foot over the disc caliper pistons. > True, but a lot of them involve tradeoffs, usually in the "stroke" of the master cylinder. A smaller bore in the MC will provide good pedal feel and acceptable pedal effort, BUT is not often workable in modern braking systems as the pedal will eventually "bottom out" on a full-effort, high-speed, ABS-active stop - definitely something you don't want to happen. Likewise, there may not be enough room to leave enough pedal left in a one-circuit-failed condition. Yes, it *can* work, but there's plenty of reasons why it doesn't. That said, in a light car (<2500 lbs.) I agree that a power booster can probably be optional, although you probably won't see it with ABS for reasons given above. Additionally, a litigation-sensitive corporation isn't going to release a vehicle for production requiring *any* higher-than-normal pedal effort unless it's a specialty model that they're fairly confident is going to be bought entirely by enthusiasts. nate -- replace "fly" with "com" to reply. http://home.comcast.net/~njnagel |
#45
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Steve wrote:
> Bill Putney wrote: > >> Daniel J. Stern wrote: >> >>> On Fri, 28 Jan 2005, Steve wrote: >>> >>> >>>> Bill Putney wrote: >>>> >>>> >>>>> The downside of power brakes, which is a necessity with disk brakes >>>>> because they do not have the designed-in mechanical amplification, >>>> >>>> >>>> >>>> Why do people keep saying this? >>> >>> >>> >>> >>> The parrot effect, I'm guessing. >> >> >> >> No. The reality of modern consumer vehicles that will be driven by >> quite a range of ages, mental quickness, and physical strength. > > > And the pedal effort in a 4400-lb 1969 vehicle with manual disk brakes > is NOT significantly higher than the pedal effort in a Honda Accord of > today. And disk vs. drum makes no difference at all. I just don't see > whay the staement that power boost "is a necessity with disk brakes" > keeps popping into discussions. That's an honest question. So you are telling me that, in the otherwise same vehicle, a non-vacuum assisted disc brake will take no more pedal pressure and at the same time no more pedal travel than a non-vacuum assisted self-energizing drum brake? If you answer "yes", then I will defer to your experience and knowledge, though I was sure that the disc brake in that example would require either a lot more pedal pressure or a lot more pedal travel or a combination (again, depending on the games played with the master cylinder design). What say you? Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x') |
#46
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On Tue, 1 Feb 2005, Nate Nagel wrote:
> > There are *many* ways of varying the mechanical advantage of the > > driver's foot over the disc caliper pistons. > True, but a lot of them involve tradeoffs, usually in the "stroke" of > the master cylinder. Yes... > A smaller bore in the MC will provide good pedal feel and acceptable > pedal effort, BUT is not often workable in modern braking systems as the > pedal will eventually "bottom out" on a full-effort, high-speed, > ABS-active stop - definitely something you don't want to happen. > Likewise, there may not be enough room to leave enough pedal left in a > one-circuit-failed condition. You've engineered more brake systems than I have, to be sure, but I'm not sure I believe that either of these must necessarily be the case. You might be able to convince me. > Additionally, a litigation-sensitive corporation isn't going to release > a vehicle for production requiring *any* higher-than-normal pedal effort Sued for installing airbags Sued for NOT installing airbags = Sued 'cause the booster fails Sued 'cause the pedal effort was "too high" Remember, there are Federal standards for pedal effort. DS |
#47
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Daniel J. Stern wrote:
> On Tue, 1 Feb 2005, Nate Nagel wrote: > > >>>There are *many* ways of varying the mechanical advantage of the >>>driver's foot over the disc caliper pistons. > > >>True, but a lot of them involve tradeoffs, usually in the "stroke" of >>the master cylinder. > > > Yes... > > >>A smaller bore in the MC will provide good pedal feel and acceptable >>pedal effort, BUT is not often workable in modern braking systems as the >>pedal will eventually "bottom out" on a full-effort, high-speed, >>ABS-active stop - definitely something you don't want to happen. >>Likewise, there may not be enough room to leave enough pedal left in a >>one-circuit-failed condition. > > > You've engineered more brake systems than I have, to be sure, but I'm not > sure I believe that either of these must necessarily be the case. You > might be able to convince me. Actually, not really. I never engineered a brake system from scratch, unless you count mixing amd matching parts on my own personal vehicles. But I have seen what happens when you get something a little off, like the MC bore size and your 70 MPH panic stop turns out to be a little more interesting than you planned on when the ABS' hydraulic accumulators suck all the fluid out of the MC. Whoopsie! Keep in mind, however, that most of the stuff I worked on professionally was light trucks - these issues may not actually surface for passenger cars. The point that I was trying to make is, simply, that there really are good engineering reasons to use a power booster, and that they become more compelling when using disc brakes as opposed to drums. > > >>Additionally, a litigation-sensitive corporation isn't going to release >>a vehicle for production requiring *any* higher-than-normal pedal effort > > > Sued for installing airbags > Sued for NOT installing airbags > > = > > Sued 'cause the booster fails > Sued 'cause the pedal effort was "too high" > > Remember, there are Federal standards for pedal effort. > Yeah... really, it boils down to how much room do you have between the top of the pedal stroke and the floor of the car (don't want to have the pedal too high, that would be bad ergonomically - you should be able to get your foot on it without taking your heel off the floor) and can you juggle your bore sizes and/or linkage to get a reasonable (or Federally mandated) pedal effort within those parameters while not having the pedal go to the floor either with one circuit failed or during a full ABS stop from whatever your maximum design speed is. If you can't, then you go to a power booster. I'm sure that someone could probably give a rough, hand-waving estimate (like I have above, but a more informed one) as to appx. what vehicle weight that starts to happen at... but the point is, that weight would be significantly higher for a drum brake car because a) they require less fluid movement (or should, if the shoes are properly adjusted - since they have positive return springs you really can't count on that though unless self adjusters are included) and b) they require less line pressure. nate -- replace "fly" with "com" to reply. http://home.comcast.net/~njnagel |
#48
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Steve wrote:
> Bill Putney wrote: > >> Daniel J. Stern wrote: >> >>> On Sun, 30 Jan 2005, Bill Putney wrote: >>> >>> >>>>> AMC bought their automatics from other makers (GM Hydramatics from the >>>>> early mid '60s through '71, Chrysler Torqueflites starting in '72). >>>> >>>> >>>> >>>> In either case where does the "never existed" part come in? >>> >>> >>> >>> >>> The part where there was any such a thing as an "AMC automatic >>> transmission". >> >> >> >> Any reasonable person would accept referring to a transmission that >> was used in AMC vehicles as an AMC transmission. Key word being >> "reasonable". > > > > 'Scuse me while I pick my jaw up off the floor! > > I've *NEVER* run anto anyone who thought AMC ever built their own > transmissions before. And you still haven't. 8^) I was told that the trannies used in AMC vehicles (in my terminiology "AMC trannies") were what was used in the subject vehicle. At least two people reading did not take that to mean that AMC built those trannies. I wasn't intentionally being ambiguous, but I figured that anyone who knew the score would take it to mean what I had intended. So let's see. To apply this rule, no one can ever refer to a wheel that fits Chevrolet vehicles (as well as certain other brands) as a "Chevrolet wheel", or a wheel that fits a Chrysler vehicle (as well as certain other brands) as a "Chrysler wheel"? Is that what we're saying here? Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x') |
#49
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Nate Nagel wrote:
> Daniel J. Stern wrote: > >> On Tue, 1 Feb 2005, Nate Nagel wrote: >> >> >>>> There are *many* ways of varying the mechanical advantage of the >>>> driver's foot over the disc caliper pistons. >> >> >> >>> True, but a lot of them involve tradeoffs, usually in the "stroke" of >>> the master cylinder. >> >> >> >> Yes... >> >> >>> A smaller bore in the MC will provide good pedal feel and acceptable >>> pedal effort, BUT is not often workable in modern braking systems as the >>> pedal will eventually "bottom out" on a full-effort, high-speed, >>> ABS-active stop - definitely something you don't want to happen. >>> Likewise, there may not be enough room to leave enough pedal left in a >>> one-circuit-failed condition. >> >> >> >> You've engineered more brake systems than I have, to be sure, but I'm not >> sure I believe that either of these must necessarily be the case. You >> might be able to convince me. > > > Actually, not really. I never engineered a brake system from scratch, > unless you count mixing amd matching parts on my own personal vehicles. > But I have seen what happens when you get something a little off, like > the MC bore size and your 70 MPH panic stop turns out to be a little > more interesting than you planned on when the ABS' hydraulic > accumulators suck all the fluid out of the MC. Whoopsie! > > Keep in mind, however, that most of the stuff I worked on professionally > was light trucks - these issues may not actually surface for passenger > cars. The point that I was trying to make is, simply, that there really > are good engineering reasons to use a power booster, and that they > become more compelling when using disc brakes as opposed to drums. > >> >> >>> Additionally, a litigation-sensitive corporation isn't going to release >>> a vehicle for production requiring *any* higher-than-normal pedal effort >> >> >> >> Sued for installing airbags >> Sued for NOT installing airbags >> >> = >> >> Sued 'cause the booster fails >> Sued 'cause the pedal effort was "too high" >> >> Remember, there are Federal standards for pedal effort. >> > > Yeah... really, it boils down to how much room do you have between the > top of the pedal stroke and the floor of the car (don't want to have the > pedal too high, that would be bad ergonomically - you should be able to > get your foot on it without taking your heel off the floor) and can you > juggle your bore sizes and/or linkage to get a reasonable (or Federally > mandated) pedal effort within those parameters while not having the > pedal go to the floor either with one circuit failed or during a full > ABS stop from whatever your maximum design speed is. If you can't, then > you go to a power booster. I'm sure that someone could probably give a > rough, hand-waving estimate (like I have above, but a more informed one) > as to appx. what vehicle weight that starts to happen at... but the > point is, that weight would be significantly higher for a drum brake car > because a) they require less fluid movement (or should, if the shoes are > properly adjusted - since they have positive return springs you really > can't count on that though unless self adjusters are included) and b) > they require less line pressure. > > nate > One more thing I meant to add... yet another reason why the "my '67 whatever had manual brakes and stopped just fine" does not translate over to a similar weight modern car *not* requiring a power booster... I've been told, although I have no hard numbers to back this up, that old asbestos brake linings actually have a higher coefficient of friction than most modern linings. I don't have enough experience to make a definitive statement on this but I will say that my '62 Stude with stock brake linings (still original, only 24K miles give or take a few) stops just fine without the power booster. However, I've heard people with near identical cars switching over to power because they claimed that the brakes required "too much effort." I suspect that that is because the brake shoes have been replaced with modern linings that work, but require more pressure to work *well.* I can tell you that trying to stop a '64 Stude with *disc* brakes and a failed power booster is a firewall-bending exercise, but that's not entirely relevant to this discussion, other than the single data point that Studebaker apparently felt it necessary to mandate a power booster for all disc brake cars, for whatever reason. Finally, stainless braided brake hoses are badass. This has *no* relevance whatsoever to this discussion, but I just felt like throwing that out there. I just replaced the front hoses on my 944 yesterday as the originals were well past their "best before" date (and the stainless ones were half the price of factory, even better) and the pedal feel is astonishingly good - and I haven't done the rears yet! Now the sludge that came out of the clutch slave when I bled it... that wasn't so badass. Hope that's not a sign of an impending future repair, 'cause it looks like a royal PITA, unless you pull the starter first. Why Porsche in its infinite wisdom didn't put the starter and the clutch slave on opposite sides of the bellhousing is beyond my ken... nate -- replace "fly" with "com" to reply. http://home.comcast.net/~njnagel |
#50
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Bernard farquart wrote:
> "Bill Putney" > wrote in message > ... > >>Daniel J. Stern wrote: >> >>>On Sun, 30 Jan 2005, Bill Putney wrote: >>> >>> >>> >>>>>AMC bought their automatics from other makers (GM Hydramatics from the >>>>>early mid '60s through '71, Chrysler Torqueflites starting in '72). >>>> >>>>In either case where does the "never existed" part come in? >>> >>> >>>The part where there was any such a thing as an "AMC automatic >>>transmission". >> >>Any reasonable person would accept referring to a transmission that was >>used in AMC vehicles as an AMC transmission. Key word being "reasonable". > > > Only if they had no clue how parts are sourced and > put together, or what the difference between a part made > by a company & just installed. So you would *never* refer to certain wheels in a junk yard as "Chevrolet wheels" or "Ford wheels". You would first find out who manufactured the wheels and reference them that way. Or how about cell phone chargers? If I wanted to buy a charger for my Motorola cell phone, I would walk into a store and ask for a Kikosuki charger because they are the company who made it, and the store owner would immediately know it was for a Motorola phone even thought Kikosuki makes chargers for 3 other brands of cell phones. Let's get real. > Anyone who thinks International Harvester products were > *under* engineered has no concept of what they are talking about. Well - I agree with you on the under-engineered part - except for that tranny. It was ridiculous to put that tranny in that heavy a vehicle with no cooler. The proof in that pudding was having to replace the fluid every 20k miles in a time when no one ever changed ATF. The over-engineered aspect of the IH vehicles was also their demise - their trucks and Travelalls could not compete with the lighter vehicles. Nor could the Scout compete witht he lighter more nimble competition. Not saying over-engineering is necessarily bad, just not competitive in a very competitive consumer market. BTW - I did things to that Travelall that would have totally done in many other vehciles, so I hear you on the over-engineered thing. It was heavier than anything. IH dealers used to brag that "our engines are 600 pounds heavier than the equivalent Ford engine!" And that's what did them in. Same with the 1942 Gravely tractor that I used to cut the grass while growing up. > I say this as the owner of a forty year old four cyl. scout that came > factory with sodium filled valves, just because it seemed like > the way to do it. Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x') |
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