GM head lights

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Tony, That van has 4 wheel ABS the rear sensor is actually in the transmission tailshaft. no such animal as front wheel only ABS on ANY make.
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Steve W. wrote:

Then my van simply sucks. Not once has either rear wheel ever pulsed the ABS like the front wheels. And yes, it is easy to hear and feel it in a cargo van. In fact it's noisy as hell!
--
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it
Since the rears only contribute 20% or less of total braking power it is real doubtful you would feel it when it engaged the ABS. My 95 Conversion has 4wheel ABS and you can't feel it when the rear works.
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Steve W. wrote:

How do you know it does work?
Even so, with no rear sensors letting it know which side is locked up, it would have to pulse both sides! Shitty setup if I ever heard of one.
--
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wrote:

Think about the typical plumbing of the rear brake lines. A single line runs to the rear axle where it connects to a block that then distributes the pressure to both wheels. Only need one sensor, only one line to pulse, that sensor is in the tailshaft of the transmission.
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Mike Levy wrote:

And before ABS, the plumbing to the right and left front brakes were also on the same line, distributing the same pressure to each front wheel. They changed the front, why not the rear also? When towing and adding 750 pounds of tongue weight to the rear (add in the leverage factor and it's more than an extra 750 pounds to the rear wheels), they would be capable of more than the normal 20% braking. Why not use it? I know, I'm just being anal. They aren't going to design anything different for the few who use the vehicle for towing.
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Ahh, it is not a myth. I DO understand physics. It is your position which is the myth.
1. ABS is designed to maximize breaking without locking up the wheels. 2. The MAIN reason #1 above is important is because skids result in longer stopping distances under most common road conditions. In some situations, such as built up "damning" of snow or on some gravel surfaces, some skidding results in the shorter stopping distance. 3. Steering during braking, while still important, is a SECONDARY goal of ABS. 4. #2 above is supported by the underlying concept in physics called starting/standing coefficient of friction vs. sliding coefficient of friction.
On a typical rubber on pavement or blacktop situation, the sliding coefficient of friction is less powerful than the starting coefficient. In a skid, the sliding coefficient of friction is in play. When the maximum amount of resistance is applied against the wheel rolling (braking pressure just short of resulting in a lockup), then it is the starting/standing coefficient of friction in play where the rubber meets the road. Since it is basically impossible to precisely apply the maximum brake pressure just short of a lockup, ABS does the next best thing it can. And that is to very quickly back the braking pressure off a little. Then it almost immediately allows the braking pressure to climb again. As soon as it senses that lockup is again starting, it backs the pressure off a little very briefly. This is why there is a rapid pulsating effect when ABS kicks on a long hard braking. Essentially, it results in the braking pressure fluctuating a little under to a little over the optimum force.
Most folks just don't understand this because some of the forces at work are outside of their normal realm of observation. I have argued this at length with others on usenet. In addition to some limited background in physics, I also researched that shorter stopping distances are the primary goal of ABS and sited my sources. The opposition couldn't find a single shred of credible research to back them up.
But anyway, for something new to try and make the point easier to understand, I came up with a new analogy. Let us for the sake of argument, grossly exaggerate the difference between the values of starting and sliding coefficients of friction (of tire compounds on typical roadways). Let us say the sliding coefficient on the car is small but not zero. This would mean the car with locked up wheels would skid a LONG way before finally coming to a stop. Zero value would result in never coming to a stop (barring air resistance or obstacles etc.).
Okay, on the other side, let us say that the starting/standing coefficient is infinite. This means that the car will go only exactly as fast as the wheels turn. Not a hair more or less, but EXACTLY the rate as the wheels turn. And the rate the wheels turn then, would be a function of force of inertia (speed and mass of car) pitted against resistance force of brake shoes or pads. If the brakes were powerful enough to resist the inertial force up in 2 seconds, then that car would be stopped in 2 seconds flat because the infinite friction of the tires would not allow a skid. Basically, you are able to employ 100% of the braking force towards overcoming momentum.
In the real world, if the wheels lock up, you are ONLY getting the resistance of sliding friction, which is not as strong as starting/standing friction and the braking system in MOST cases. There ARE exceptions to this. But my main original point still stands, that ABS results in shorter stopping distances in most conditions, for most drivers most of the time. Studies and tests bear this out as well.
I think a really really good driver could be nearly as efficient as ABS under the conditions that ABS works best, and that same driver could OUTPERFORM ABS by a good bit in those situations where ABS works least well. So, if you are real good AND do not ever panic, you probably are better off without ABS. Also true of you drive a lot on gravel roads or slippery roads with a layer of snow on them. Because then, the starting/standing coefficient of friction actually drops lower than the sliding coefficient is when figuring in the damning effect of pushing snow or gravel.
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SgtSilicon wrote:

This is where your problem is, this was not the goal of ABS. ABS was designed to prevent the wheels from locking so you can maintain steering, maximizing braking was not a design goal and simply cannot be done with ABS. The "better braking" is what people are starting to think and is resulting in more dangerous drivers who will over drive the situatuion.

Yes, skids do but proper braking is applying enough pressure to stop without skidding. The untrained driver will simply push the pedal as hard as they can and cause a skid which is where ABS does help, but anyone who has actually tried to learn how to drive can easily feel the right amount of pressure. But as ABS becomes more standard it becomes harder to learn this feel because a slight wheel hop at that threashold will trigger the ABS (which is my main problem with it) and result in loss of braking power as the ABS releases pressure. I have felt it many times as one wheel touches a crack in the pavement the ABS system will detect a slight change in wheel speed and release the pressure causing the vehicle to jump forward and then attempts to build pressure back up to the point where I already had it. ABS would work in a perfect world where there are no pavement cracks and patches or potholes but I never drive on perfect roads. Unless ABS can have some way to sense road conditions there isn't any way it could ever decrease stopping distances. Sure it will in a lab test because they have perfectly paved roads.

Steering was the whole reason ABS was designed/invented, go back and do the research and look at the history (i think it was Volvo that first put in into production) and the design goals and reasons they designed it.

Yes and this is the problem. I'm a very uncoordinated person and certainly not the best driver in the world but I can hold a brake at that correct amount of pressure and if someone such as I can do it then anyone else can do it easily too. I am well below average in eye-hand coordination, could never play sports or video games so that means it only takes below average coordination to beat ABS. Each time the ABS system releases the pressure the stopping distance increases when compared to a person holding the brakes at the maximum pressure point. The old ABS system in the Chrysler we had pulsed maybe once a second, the current GM I have does 3-4 times a second. Many people who believe ABS can stop better will claim it pulses millions of times a second therefore it can react faster than a human but while it may read the sensors that fast the mechanicle parts in the brake system can't react that fast. Think about the old rusty car pulling away from a stop and you hear the brakes squeak a couple wheel revolutions that old car ABS wouldn't even work because it take a good couple seconds for the pads to release pressure :) But even a modern good working system won't release in a microsecond which would be required for millions of pulses per second on the brake system. So a few times a second seems to be the average and each time it backs off the pressure your extending the distance, so the 3-4 times a second you slightly extend the stopping distance by not breaking at maximum adds up.

I don't know who you opposition is and what research you have done, but the goal of abs was steering control. There have even bee documentaries on the discovery channel/tlc/history channel when they go into the history of cars and such where they talk about steering control. Traction control has become a secondary goal of ABS systems though.

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wrote:

- I do not have a problem.
- Shorter stopping distance was the primary goal of ABS.
- Maximizing breaking under many circumstances is done better than a human could do it.

- It is not easy to apply EXACTLY the maximum brake pressure short of a lockup. Scientific tests prove this, because ABS results in shorter stopping distances. If it were so easy for people to outperform the ABS, professional test drivers would do BETTER without ABS engaged. But they do not. Their stopping distances are shorter with ABS engaged.

Wheel hops are not the norm. They certainly are not rare to be sure, but in total, most stops are achieved shorter with ABS. You can bring up all kinds of perimeter variables, but it doesn't change that most of the time ABS performs better than the driver would/could.

Well, just as the "lab" supposedly has perfectly smooth roads, you seem to drive on nothing but bomb crater alley every waking moment. I think I'll just leave it at that. Reasonable people can make of it what they will.

Not according to everything I have found on the subject. Shorter stopping distance is numero uno in what I have looked up. Shorter stopping distance was always listed 1st and/or more prominently than maintaining steering. But you know what, it really doesn't make much difference. I was rebutting the notion that shorter stopping distance with ABS is a "myth".

What you are probably doing is applying a braking force that is not causing a lock up, but yet is not as much pressure as could be applied within the threshold. I have anecdotal evidence of my own as well, but I value controlled testing more than I do what you or I have experienced just on our own. That being said, here is my 2 cent anecdote. I am fairly well coordinated person; probably above average judging by some things. I also can usually stay in control under stress. I have been "battle tested" so to speak. But anyway, there have been a couple of times where I mashed the brake pedal down because of a possible / probable imminent collision. The ABS was activated before I had time to even fully understand what was happening in the cerebrum. "Fight or flight" was ALREADY engaged. Thank God so was the ABS. What I did realize, was that I would have probably locked up the wheels, at least for maybe a second or part of one, had I not had ABS. In less than another second there would have been a collision. Not all hard braking situations involve longer distances and more time to react.

The old rusty car. A couple (2!) seconds. I think I'm just going to let that kind of sit there. I'm starting to see where your education on the subject comes from.

People can say anything. Megahertz range sounds a bit outside reality.

Wrong, because feeling for the optimum pressure actually doesn't work as well as you think it does (tests bear this out), and locking up the brakes is FAR worse yet. In the controlled tests the drivers do not have to face the panic factor, and STILL they stop shorter with ABS engaged. This proves without any doubt that at least the test drivers are not applying as optimal a braking force as the ABS can. And besides that, in the real world, panic, fear and hormones play a real part. Real people CAN and DO lock up the brakes on non ABS equipped vehicles. You think you are beyond that reach. Fine. I won't argue with you on it. But I KNOW for a fact that skids are COMMON in real world situations. Go talk to any traffic accident investigator.
You can go on all day about how you think you and most everyone else can "beat the machine" (which I disagree with) when it comes to achieving applying just the right amount of brake pressure, but are you honestly going to try and pretend that even skids are superior to ABS stops? Or, are you going to pretend that skids are not part of real world emergency braking. If you neither deny that skids are a part of real life emergency braking, or that skidding is generally an inferior way to brake, you must then admit ABS is a benefit if for no other reason!

I watch DSC, TLC, SCI, and all that stuff too. I do not deny, nor have I ever denied that steering control or traction control are benefits of ABS. What I have said, is that shorter stopping distance is/was the primary driving force in ABS. More importantly what I have said, and really the main point I wanted to convey, is that ABS actually DOES improve stopping distances/times, and that fact is NOT a myth. It had been stated that ABS results in longer stopping distance/time. I wanted to rebut that because, it just isn't so.
Here's some reading for you, in case you are interested:
From http://www.culpepperlaw.com/abs.htm :
The History of ABS
When a driver of a vehicle hits conventional brakes hard, the wheels may lock causing the vehicle to skid, especially on wet and slippery roads. Antilock brake systems provide the capability for shorter stopping distances and the ability to steer and to maintain control during hard braking, especially on wet and slippery surfaces.
From http://www.informationheadquarters.com/Computer/Anti-lock_brake.shtml
Anti-lock braking system
An Anti-lock Braking System (commonly known as ABS) is a system on motor vehicles which prevents the wheels from locking while braking. ABS is a very important safety feature, because vehicles become very unstable when the wheels are locked, braking becomes inefficient and so braking distances become very long.
From http://www.hwysafety.org/safety_facts/qanda/antilock.htm :
1. How do antilock brakes work? Antilock brakes are designed to help drivers avoid crashes. When a driver hits regular brakes hard, the wheels may lock and the vehicle may skid. Wheel lockup can result in longer stopping distances, loss of steering control and, when road friction is uneven, loss of stability if the vehicle begins to spin. The main advantage of antilocks is that they can reduce these problems on wet and slippery roads. Antilocks work with your car's normal service brakes to decrease stopping distance and increase the control and stability of the vehicle during hard braking.

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Oh yeah. I forgot to reference this in the other follow-up I just posted. The following is a link to a study conducted by the US DOT. They actually employ scientific principles, rather than Eugene (or other random anecdotal) principles:
http://www-nrd.nhtsa.dot.gov/vrtc/ca/capubs/braketst.pdf
It CLEARLY shows that ABS results in better braking distances than the exact same vehicles with the same drivers do without ABS on. Go read the report. Read it again if you have to. Then go look at your own posting (quoted somewhere below convenience) which goes something like this:
"maximizing braking was not a design goal and simply cannot be done with ABS. The "better braking" is what people are starting to think and is resulting in more dangerous drivers who will over drive the situatuion."
Not only can it be done, it IS DONE! And consistently over averages I might add.
Hehe. I also love the part of the posting I read somewhere in this group (maybe not by you) about salesmen cooking up the false notion of ABS as a safety feature. Yeah; everyone is all caught up in the "myth", except for those like you who know what's really going on. Hehe. What a hoot.
Unless you can site credible articles or sources which actually scientifically contradict the references I have sited, I suggest you stifle it, before you really embarrass yourself.
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Unless I am mistaken (which is possible) ABS was designed & introduced for Airplanes in the 1950's. It then slowly migraged into the high end automobiles and then down to the cheap crap.
The biggest drawback to ABS on car's is that it allows people who would have previously rear-ended another vehicle with minor consequences to now steer off the road rolling their cars with major consequences.
That being said there are differing calibre's of ABS. For example my 1986 Lincoln Continental had ABS that felt pulsed so fast it felt like stepping on a vibrator when it was active (as discovered on a night with freezing rain). I had the misfortune of Driving a Neon & (just for shit's & giggles) tried out it's ABS. The ABS on the Neon felt like a mechanical switch being switched on and off. Felt like 2 hertz, probably closer to 20 in reality though. My Old's isn't quite as fast as my Lincoln but still WAY faster than the Neon.
Question on stopping distance: The Lincoln would stop faster (pound for pound) than the Neon without a doubt. My personal experiance with my cars that have had ABS is that, applied correctly (slamming the brakes on & fully utilizing the ABS) they will usually stop faster than conventionally equipt cars. However trying to Modulate ABS yourself will cause a huge extension in stopping distance.
I'm not bad at pedal modulation (my father taught me to drive in a VW with bald tires in the winter time) but I am no match for ABS. I have 1 control for 4 wheels. ABS has 1 control per wheel (in the proper systems). So, if I am trying to prevent 1 wheel from skidding (threshold braking) I am underbraking 3 others. Good ABS has the potential to react much much faster on an individual wheel basis than any human can ever hope to match.
I understand some trucks had an early form of ABS mounted on the driveshaft that only controlled the rear axle's skidding. The primary purpose of that (I believe) was to prevent the rear-end from locking up in unladen conditions.
x
PS The Lincolns brakes were sweet but the rotor's were $150 each for the fronts b/c of the ABS adaptors. I somehow doubt that the Neon's rotors are anywhere near that price, adjusted for inflation. With of course the corresponding quality of braking.
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Full_Name wrote:

I never saw it, but I heard some light duty trucks had early rear "anti-lock" brakes that simply increased rear braking proportionately to how much weight it was carrying. The more it sagged, the more rear braking.
What this has to do with GM headlights I don't know. ;-)
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wrote:

You noticed that too eh? ;-)
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It transformed. Subject was loss of manual control of lights. Wound its way into loss of manual control of braking. The pros, the cons etc.
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wrote:

Correct about 1st used on Airplanes and the time frame. I would add that it was invented by the German company Bosch. In fact, the "ABS" letters actually originally were derived from "Antiblockiersystem" which was the name Bosch had given it.

I don't know if that is the biggest drawback or not, but like anything in life one thing can lead to another many times.

So true. Some systems are definitely superior to others. For sure 4 wheel ABS with true independent control is the best. My 2001 Camaro has a very rapid pulse cycle. Without being scientific, I would estimate perhaps 20 Hertz for the mechanical pulse feel.

Well sure. Once ABS is doing it's job and gripping as tightly as possible without going into a skid, your brakes themselves are a very important part of the equation. All discs compared to part drum. Or Discs with big heavy duty rotors, pads and pistons compared to wimpy stuff. A heavy car with outstanding brakes often can do better than a lighter car with poor brakes.

My personal experience is right on par with yours. I learned my driving on a '69, two wheel drive, "3 on a tree" manual tranny Chevy pickup in Wisconsin's winter wonderland. I too learned manual brake modulation, or "pumping" as we used to call it, and totally agree that a good ABS can beat my ass most any day of the week.

I've read something like that at some point I believe. I don't remember much about it, but it certainly doesn't seem like one of the better ABS implementations.
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SgtSilicon wrote:

What makes the ABS on my 2000 GM cargo van suck so bad, is the fact that once the ABS is activated, it continues to pulse for about 1.5 seconds, even if the tire IS gripping the road. One and a half seconds of ABS braking is simply FAR TOO LONG! Now add in the situation where the ABS is activating over and over for 3 or 4 cycles. Now we have 4.5 to 6 seconds of partial braking! This lag time of having partial braking for so long results in longer stopping distances. I suppose if the ABS didn't disable the brakes as much as it does, and if it were much faster reacting, or *deactivating* itself when not needed, then it might actually do what it is intended to do. But as it is, it sucks, and it increases stopping distances in most situations in my real life driving situations.
--
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wrote:

Tony, what kind of situation on God's green earth has you braking for as long as 6 whole seconds??
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SgtSilicon wrote:

It wasn't on gods green earth, it was on mans bumpy highway at 70 or so mph and an accident in front of me. Luckily, (yes luckily!) I was pulling a trailer and used those brakes manually. Yes, the trailer with a couple tons in it slowed me down better than the ABS crap. And yes, using them manually, with all four wheels on the trailer locked up most of the time. If you have ever pulled a trailer with brakes, you get a feeling for it and can easily feel if the trailer is pushing you ahead or holding you back. It held me back.
--
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wrote:

I only asked because 6 full seconds is a LONG time for emergency braking in most situations, but I can see where an interstate could give you a pretty good preview.
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SgtSilicon wrote:

Yes it did. Almost had to change my shorts after that one.
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