It's normal to skid on ice. Does your truck have anti-lock brakes? If not, the operation is as expected. Tires don't grip on ice any better than your shoes do. If it does have ABS, the system kicks out at under about 5 miles per hour. Above that, there's a limit to what the system can do. A skidding tire has no traction and can not be steered. The purpose of the system is to prevent you from losing steering ability due to braking. It can't help in a skid caused by going around a curve too fast. Had to throw that comment in for the benefit of other readers. Too many people drive way too fast because they think the ABS system can magically correct their driving mistakes. The systems were first developed for aircraft landing on aircraft carriers, but the pilot is still expected to have the plane lined up with the runway.
There's also two totally different anti-lock systems. Most trucks have rear-wheel-anti-lock (RWAL) systems that prevents rear-wheel lockup only. It modulates brake fluid pressure to both rear wheels together, and does absolutely nothing to the front wheels. It works strictly by the RATE at which the rear wheels are slowing down, not their specific speed in relation to anything else. 4-wheel ABS systems look for the wheel that's spinning the fastest and disregards it. Of the other three, it looks for one that's spinning 20 percent slower than the other two, and modulates pressure to that one. It rechecks wheels speeds 15 times per second.
If you have that 4-wheel ABS system, all it can do is prevent your braking from making a tire skid. It can fully release one brake but that doesn't mean that wheel is going start turning immediately again if it's on ice. It takes time for the pressurized fluid to leave a brake caliper, so a wheel can continue skidding for a few seconds. That would not happen on a dry road where the tire has traction. 4-wheel ABS systems are real effective on ice, but if the front starts skidding from just turning the steering wheel when you're going too fast, applying the brakes isn't going to overcome that type of skid.
Both ABS systems have a yellow warning light that will turn on for six seconds when you turn on the ignition switch. If you don't see that, you don't have ABS. The 4-wheel system has a large complicated hydraulic controller near the master cylinder. Most, (but not all) of them use a pump to pressurize the brake fluid to about 2200 pounds of pressure. You will likely hear that pump running for a few seconds right after you start the engine. You will also hear all kinds of banging and buzzing when the brake pedal is pressed AND it's working to prevent a skid.
There is no pump and just a small valve assembly on the left frame rail for the RWAL system. If you pay attention during a hard stop, when that system activates, the brake pedal will slowly sink closer to the floor as the brake fluid is released from the rear brakes, then new fluid is reapplied multiple times per second. The "released" fluid flows back to the master cylinder reservoir when you release the brake pedal.
Another interesting note is that it is absolutely not true that you can count on shorter stopping distances when you have anti-lock brakes. I cringe when I see how closely some people tailgate thinking they're smarter than everyone else because they can stop quicker. I have ABS on a '93 Dynasty, and it's true, I will just about tear the seat belts off the hinges when I purposely test the system's operation on sand in a parking lot. That Bendix-10 system is extremely effective, ... But that is not its purpose. It is only meant to let the driver maintain steering control. A friend who used to work with me at the dealership, so he drove a lot of Chrysler products with ABS, is now a county deputy. The department used to have a lot of Chevy Caprice Classics with the Bendix-9 ABS system. The only difference is my Bendix-10 system has a tenth valve to isolate the rear brakes from each other so they can be controlled individually. Rear brakes provide a very small percentage of total stopping power so there was something else different in the design of the car because he said stopping distances were increased greatly on those cars. In a panic stop, the car would just go and go, and slow down very gradually. Squad cars without ABS stopped much quicker but you risked losing steering control. Personally, I prefer my car because if something, (or someone) surprises me and I slam on the brakes, there's little chance I'm going to react fast enough to steer around the car that ran the red light. I'm happier knowing I'm going to be able to stop fast enough to avoid a crash, but I still have to worry about the person on the cell phone behind me.
Friday, December 23rd, 2011 AT 11:13 PM