Brakes unable to stop runaway Lexus in California?
in [Toyota]
|
From: Heron McKeister on 17 Nov 2009 16:11 "hls" <hls(a)nospam.nix> wrote in message news:ROidnVEBrZ9cVpzWnZ2dnUVZ_oCdnZ2d(a)giganews.com... > > "Heron McKeister" <not(a)home.com> wrote in message > news:3tjMm.19831$gi1.12545(a)newsfe19.iad... > > "hls" <hls(a)nospam.nix> wrote in message > > news:sJWdnfF9FOHXI5zWnZ2dnUVZ_oKdnZ2d(a)giganews.com... > >> > >> "Ray O" <rokigawa(a)NOSPAMtristarassociates.com> wrote in message Before > >> power assisted brakes were introduced, people > >> > routinely stopped vehicles by stepping hard on the brake pedal. > >> > >> That is true, Ray, but also in those days we had front and rear drums, > >> for > >> the most part. > >> Discs required a lot more pressure than drums, hence the power assist > > brakes > >> became > >> a necessity rather than just a luxury convenience. > > > > > > I had 4 wheel disc brakes on my '74 Fiat 124 Spyder, > > was the best stopping vehicle I had owned at the time > > and it neither had nor required power assisted brakes. > > > > Of course, there are exceptions to everything anyone says on here. Including that statement? > Everybody > seems to scan for the exception rather than to consider the truth of the > principle. Really, everybody? > Weight plays a big part in this. Obviously bicycles and motorcycles may > also have > disc brakes, and they can be stopped easily by a standard human being > because they > weigh so little. But no one was addressing cycles. > As the car gets heavier, it becomes harder and harder to > stop an > unassisted disc brake system. The design of the braking system is another > factor... > the makeup of the pad, the surface area of the pad, the size of the caliper > pistons ( > thus mechanical advantage designed into the system) all enter in. Not to mention such esoterics as the boiling point and vapor pressure of the fluid, the universal gravitational constant ... ;-) > Drum brakes have a pseudoservo action which draws one of the shoes onto the > drum surface and gives some mechanical advantage. Dependent upon application, ie whether a twin leading or leading/trailing design and the direction of rotation. > They may also have a much > larger surface area than disc brake pads. Are you alluding to swept area or static contact surface? > Even so, power drum brakes were > used > in a lot of American cars before discs took over. > > Disc brakes, per se, require more pressure than drum brakes, in general. > Their > advantages, IN GENERAL, are that they do not fade as badly when heated, > and they perform better in the wet. Unsprung weight arguments can be made, > but you can engineer lightweight drum systems that could compare with many > disc caliper systems. Porsche used them for a long time. I was always partial to the finned aluminum GM drums. > For the larger and heavier American cars of the time (my reference), Implicit perhaps, I saw no explicit reference. > you had > to have power disc brake assists to offset the weak and lazy asses of most > Americans. No, reducing the ratio of master cylinder piston to aggregate wheel cylinder cross sectional or working surface areas (being careful to consider volume amounts and pedal travel) would accomplish the mechanical advantage provded by power assist. But I'm just screwing with you, we're in fundamental agreement.
From: Heron McKeister on 17 Nov 2009 16:14 "hls" <hls(a)nospam.nix> wrote in message news:ro-dnUYCxMysS5zWnZ2dnUVZ_vidnZ2d(a)giganews.com... > > "dsi1" <dsi1(a)humuhumunukunukuapuapa.org> wrote in message news:ugkMm.51080 > > I've had several 1972 Fiat 124 Sports Coupe. They all had standard vac > > operated brake boosters. The coupes also had a valve that measured the > > angle of the body to the rear axle and reduced line pressure to the rear > > disks on hard braking to prevent the rear wheels from locking up. A nifty > > idea. > > Now that you mention it, a friend of mine has an Alfa Romeo from that time > period. > It has vacuum, but gets it in a strange way. Ive seen it, and my friend has > attempted to > explain it, but I am not satisfied that I understand it completely. A > vacuum line is tapped > into the head near the exhaust port. I dont know that it goes directly to > manifold vacuum > or what. Maybe someone here knows the details of this unusual bit of > Italianism. Not familiar with that. Could it have been something like a low pressure source (using the bernoulli effect for high speed flow), possibly boosted by a vacuum amplifier, for low intake manifold vacuum conditions present during periods of acceleration concurrent with high exhasut gas velocities? An altogether hilarious concept, no?
From: Heron McKeister on 17 Nov 2009 16:20 "hls" <hls(a)nospam.nix> wrote in message news:CYOdnUyCZahXZZzWnZ2dnUVZ_vGdnZ2d(a)giganews.com... > > "MG" <rebore78052(a)mypacks.net> wrote in message news:dtlMm.2751 > > > > This entire story illustrates yet again the beauty of the manual > > transmission. Depress clutch (or not), take it out of gear, end of > > problem. > > You betcha! And if (seldom) you have to repair it, you can do it in the > back > of a small shop in Avezzano with ordinary hand tools for the most part. > > Im glad you brought this up. I am not really a fan of automatic slushboxes. My experience (albeit dated) has been that most automatic transmissions are not much more, if at all, demanding to repair than standards. The former usually involves only replacing friction surfaces, gaskets o-rings and possibly snap and sealing rings. They most often don't require the replacement of bushings, pumps, sprags, gears, servos ... Once failed the latter is likely to involve, if not require, replacement of synchronizer rings, dogs, shifter forks, ball and/or needle bearings sets, possibly gears or shafts.
From: Heron McKeister on 17 Nov 2009 16:25 "hls" <hls(a)nospam.nix> wrote in message news:DMGdnVZK6rC8KJ_WnZ2dnUVZ_vGdnZ2d(a)giganews.com... > > "dsi1" <dsi1(a)spamnet.com> wrote in message news:5eqMm.20048 > > I doubt there's much validity that vacuum assisted brakes were required > > because of the advent of disk brakes. My first car, a 67 Barracuda had > > drums and vac boost, as did most cars of the time. That one had a tiny > > V8 - a 273! Of course, today that would be a large engine - 4.5L. :-) > > Power assist brakes, as I said, became luxury items. They were not > absolutely necessary on drum brake cars, but certainly made braking > effortless. Finally they found their way onto almost every car. > > Disc brakes on large American cars, without power assist, can be monsters. > > It is just the way things evolved. Ah for the days of non integrated proportioning and metering valves ;^)
From: hls on 17 Nov 2009 17:43
"Heron McKeister" <not(a)home.com> wrote in message news:SjEMm.17411 > > But I'm just screwing with you, we're in fundamental agreement. > I know, and I dont mind that.. I get tired of all the "yeah, but" and "what if" bullshit. There are always factors which can be swayed, moved, massaged. |