> 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.
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.
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.
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.
That's interesting - I don't know anything about that.
The Alfa I had was a little weird too. It had a SPICA mechanical fuel injection that was like a analog/mechanical computer whose workings scared me to death. The transmission and clutch was in the rear end which means the driveshaft spun at engine speeds which means the driveshaft had to be balanced to a high degree but it never was. It also had nifty inboard disk brakes and a DeDion rear suspension. The specs were advanced for the time but it was pretty much all a technological dead end.
I have no problem with manuals but the reality is that it's mainly appropriate for small sports cars. I don't want to be shifting if I've driving a bunch of kids or adults around. I wouldn't want a manual in a large family car any more than I'd want an automatic in a small VW or Fiat.
The manual will die out along with the piston engine. The cars of the future will be probably be powered with electric motors. My guess is that electric motor controllers could be programed to simulate the torque and shift take-up of piston engines. Sadly, that'll probably be the only legacy of the age of the piston engine and manual gearboxes that will survive.
Not to mention such esoterics as the boiling point and vapor pressure of the fluid, the universal gravitational constant ... ;-)
Dependent upon application, ie whether a twin leading or leading/trailing design and the direction of rotation.
Are you alluding to swept area or static contact surface?
I was always partial to the finned aluminum GM drums.
Implicit perhaps, I saw no explicit reference.
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.
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?
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.
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.
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