Anti-Lock Brakes

Not only that, many ABS systems CAN'T do anything without foot pressure on the brake pedal, even if their control relay sticks and the pump motor runs constantly. Without the master cylinder being partly activated, all the pump can do is circulate fluid around.

It all depends on the PARTICULAR ABS implementation.

My first car was a 37 chev. It could lock up on dry pavement.

Harry K

Well...this subject did not go well here. But I appreciate that everyone did just stick to the subject...

One last parting shot...

Old cars locked up their brakes because they were set up for even brake wear front to rear...and thus old cars had too much percentage of hydraulic force going to the rear brakes. And old cars also had narrow tires...

You shouldn't say that old cars locked up their brakes and then say that new cars should lock-up brakes even more. New cars lock up their brakes less...because they proportion front to rear hydraulic force and because they have wide tires.

Old cars locked up their brakes because that's what brakes do.

What does the proportion of force between front and back have to do with locking the brakes up? If you apply enough force to the pad, the brake will lock up. It doesn't matter whether the front brakes get more or less force than the rear brakes.... get enough force and the brake will lock up.

And there are times... very few of them.... but there are times when locking up the brakes is the right thing to do.

--scott

Any new car that can't lock up its brakes (ABS disabled, of course) under ideal (clean, dry, good road surface, warm temperature) conditions has defective brakes. Period, end of story.

I'm not trying to be deliberately contrary, or even unnecessarily argumentative - but your understanding of the subject is seriously flawed.

Yes, older cars had narrow, bias ply tires, but as tire technology has improved, brakes have become more powerful as well. That said, the 50 year old brakes on my Stude still lock up modern tires. The main improvements in brakes since that time are not in overall brake torque, but in fade resistance and ease of modulation. Modern disc brakes with big, chunky calipers are much stronger and flex less, therefore they are easier to modulate "at the limit."

nate

PolicySpy wrote:

Cars of fifty years ago often became race cars. They had two master cylinders...one for the front wheels and one for the rear wheels...with a lateral rod connecting them together. Then one rod came from the brake pedal to the lateral rod. The lateral rod could be adjusted with a screwdriver to vary the proportion of hydraulic force going to front and rear brakes...and that just based on the leverage of the lateral rod. Also the master cylinder for the rear brakes was smaller than the master cylinder for the front brakes. Now the race cars of fifty years ago did not have a problem with brake lockup...

Yes, but what does this have to do with anything? This is totally irrelevant to the subject of brake lockup. Why do you keep going on about proportion of braking force?

What is a "problem?" Cars of the fifties... you could lock their brakes up. Cars today without ABS... you can lock them up too.

In a racing situation there are a couple of different cases where locking your brakes up is a very important and useful thing to be able to do. There are a lot of other cases where you don't want to ever lock your brakes up. This is why skilled drivers are used, because they can make qualified decisions about proper braking under varying circumstances.

--scott

There was no problem with brake lockup because brake lockup is not a problem. They still could and did lock up the wheels if the driver applied enough force to the brake pedal.

That said, the setup that you describe while typical of race cars is not at all typical of a street car of 50 years ago. The typical street vehicle had a single reservoir/single circuit master cylinder, and the brake "proportioning" such as it was was taken care of by careful sizing of the front and rear wheel cylinders. (that is, there was no proportioning valve per se.)

Even when a system is correctly proportioned front to rear, brake lockup can and does still occur. The proportioning, however, ensures that the front wheels lock up slightly before the rear wheels so that if a driver does inadvertantly lock up the wheels the car won't become unstable.

nate

Uh... no. They were set up as I described before, to insure that front and rear locked about the same time, given an equal surface for all 4 wheels and allowing for weight transfer during braking.

And old cars also had narrow tires...

Depends on the "old car." My '66 has P255 traction "A" rated radials on it. And it can lock all 4 of them up. The only modification to the braking system was to put a set of 1972 front disks from the same chassis type- a bolt-in upgrade- and the matching prop valve on it. All factory parts.

Yes, actually: they did.

Cars have never had a problem with brake lockup. It's drivers who have the problem with brake lockup....

--scott

You sure about that? Been a long time but I recollect hat the master cylinder only had one pump that fed all four brakes and no special valving.

You just said in para 1 that old cars also proportioned the braking.

Harry K

But IF there is a speed sensor error, it will throw a code and let you know. the engineers have put fail safes into the system. Do you have any idea the amount of checks that is done on a o2 sensor? More than you can imagine.. The same is applied to all aspects of the cars. IE GM uses 3 voltage reference on the electronic throttle position 0-5v, 5-0v and a mathematical difference between the two. If it sees a slight variation beyond the tolerance it sets a code and may go into failsafe. When you talk about Traction control and stability systems, your right the wheel speed sensor does play into it. But some cars have yaw sensors. WHAT IF IT IS FAILING!!!! OMG!!!! WHAT DO I DO!!!

Trust the system to inform you of a fault, it can and will do this.

Steve. ASE Master Tech, L1 Diagnosis Subaru Tech.

No...cars are being found with brake drag with the ABS fuse in...that is eliminated with the ABS fuse out. And there are no error codes...

But in one case there is a feeling in the steering such that the problem probably is the traction control. And in fact in that case the traction control can light up...in normal driving...just showing a moment of useage but no error code.

I didn't say that before...I just here's an easy way to test for brake drag. And that's coasting distance from 70 MPH to 40 MPH...with the ABS fuse in and with the ABS fuse out.

I can't resist one more braking dynamics point:

A racing motorcycle...even a sportbike quickly converted to racing...can lift it's rear wheel off the ground during maximum braking. The front wheel...with 100% of the motorcycle and rider weight on it...does not lock up. Of course the front brake system and the rear brake system are separate...

See...maximum-braking is defined as 100% weight transfer. Well...define maximum-braking as the most braking that a particular vehicle can achive in practice. Then...define ultimate-braking as 100% weight transfer to the front wheels. Next...just say that a racing motorcycle on dry pavement and with racing tires...can achive ultimate-braking. But the racing motorcycle achieves ultimate braking without front wheel lock-up. And the racing motorcycle during ultimate-braking has 100% of the weight on the front wheel and the front brake is getting 100% of the brake force since the front brake system and the rear brake system are separate. And that's a proof...

And that's a proof...that wheel lock-up can be avoided with hydraulic brake proportioning relative to vehicle front-to-rear weight distribution and relative to vehicle weight transfer.

(A related item is that tires can achieve more than 1 G of force because they interlock with the pavement.)

In 45 years of driving, I have _never_ been in a situation where I needed antilock brakes. How do I know? Because I haven't slid into anything before having AL brakes on my Jeep, and not since I got that have I been in a situation where the AL brakes engaged in a situation that would otherwise have produced a crash.

I _DID_, however, become a passenger in my own car that _SLID_ out into an intersection from a gravel road that caused the AL brakes to work extremely poorly, and allow the car to roll into the intersection, where a regular set of brakes would have stopped easily well in advance of the intersection, but caught my driver by complete surprise. If the other driver at that intersction at the time hadn't been paying attention, my AL brakes would have gotten us hurt.

Repeal absolutely ALL laws that REQUIRE that there be a particular "safety device" on cars and simply make laws that make them available. I then will not have to buy air bags, AL brakes, traction control, etc. etc., my car will cost a _lot_ less, and I won't have the weight of these historically useless items dragging down my fuel economy for the next 10 years of my ownership of the car in question, which is how long I have to own one now because they are so friggin' expensive... due in part to all those useless things that are mandated by law, against my will, and that I have to buy anyway.

Good for you. Your experience does not mirror every other driver's experience though, especially those that drive on icy and snowy roads. That is where the new braking system does its best work. When I was 16 and just started todrive, I had one experience with sliding on a snow covered road. I learned from it. Some drivers never do.

Sounds like a driver that lacked a bit of experience and was travelling to fast for conditions. Chances are the car would have slid into the intersection anyway, but the fact is, neither of us can prove what would have happened with regular brakes. One bit feature of AL brking sysems is steering control. With wheels locked, you have none.

If the other driver at that intersction

If your driver had been paying attention, the situation would now have occurred in the first place. .