Brakes unable to stop runaway Lexus in California?
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From: hls on 16 Nov 2009 16:04 "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.
From: Heron McKeister on 16 Nov 2009 16:27 "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.
From: N8N on 16 Nov 2009 16:49 On Nov 16, 4:27 pm, "Heron McKeister" <n...(a)home.com> wrote: > "hls" <h...(a)nospam.nix> wrote in message > > news:sJWdnfF9FOHXI5zWnZ2dnUVZ_oKdnZ2d(a)giganews.com... > > > > > "Ray O" <rokig...(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. Well, you're both right - discs *do* require more line pressure than drums, but a Fiat Spyder is a fairly light car so it doesn't matter all that much. I used to have a Porsche 914 with manual discs, but in general, manual discs are pretty rare and unlikely to be found on anything but small, light sports cars. nate
From: Heron McKeister on 16 Nov 2009 16:53 "N8N" <njnagel(a)hotmail.com> wrote in message news:d8aeda5a-97c2-4b14-aa7e-89d28ce14947(a)s31g2000yqs.googlegroups.com... On Nov 16, 4:27 pm, "Heron McKeister" <n...(a)home.com> wrote: > "hls" <h...(a)nospam.nix> wrote in message > > news:sJWdnfF9FOHXI5zWnZ2dnUVZ_oKdnZ2d(a)giganews.com... > > > > > "Ray O" <rokig...(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. Well, you're both right - discs *do* require more line pressure than drums, but a Fiat Spyder is a fairly light car so it doesn't matter all that much. I used to have a Porsche 914 with manual discs, but in general, manual discs are pretty rare and unlikely to be found on anything but small, light sports cars. nate ------------------------------------------------------- I wholly concur.
From: hls on 16 Nov 2009 17:01
"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. Everybody seems to scan for the exception rather than to consider the truth of the principle. 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. 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. Drum brakes have a pseudoservo action which draws one of the shoes onto the drum surface and gives some mechanical advantage. They may also have a much larger surface area than disc brake pads. 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. For the larger and heavier American cars of the time (my reference), you had to have power disc brake assists to offset the weak and lazy asses of most Americans. |